Curious Folks Ask 2
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Curious Folks Ask 2 188 Real Answers on Our Fellow Creatures,Our Planet, and Beyond
Sherry Seethaler
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[email protected]. Company and product names mentioned herein are the trademarks or registered trademarks of their respective owners. All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission in writing from the publisher. Printed in the United States of America First Printing February 2011 ISBN-10: 0-13-705739-3 ISBN-13: 978-0-13-705739-9 Pearson Education LTD. Pearson Education Australia PTY, Limited. Pearson Education Singapore, Pte. Ltd. Pearson Education Asia, Ltd. Pearson Education Canada, Ltd. Pearson Educación de Mexico, S.A. de C.V. Pearson Education—Japan Pearson Education Malaysia, Pte. Ltd. Library of Congress Cataloging-in-Publication Data: Seethaler, Sherry Curious folks ask 2 : 188 real answers on our fellow creatures, our planet, and beyond / Sherry Seethaler.—1st ed. p. cm. ISBN 978-0-13-705739-9 (hardcover : alk. paper) 1. Biology--Miscellanea. 2. Life (Biology)--Miscellanea. I. Title. II. Title: Curious folks ask two. QH313.S453 2011 570--dc22 2010031492
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For everyone who has ever wondered
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Contents Acknowledgments . . . . . . . . . . . . . . . . . . . . xiii About the Author . . . . . . . . . . . . . . . . . . . . . xiv Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Chapter 1
Creepy crawlies . . . . . . . . . . . . . . . . . . . . . . . 1 Eight-legged epicure . . . . . . . . . . . . . . . . . . . . . . . . 1 Fancy footwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Silk architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Let sleeping spiders lie. . . . . . . . . . . . . . . . . . . . . . 3 Lazarus fly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Mile-high club. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Colorful compass clocks . . . . . . . . . . . . . . . . . . . . . 7 Reinventing oneself . . . . . . . . . . . . . . . . . . . . . . . . 8 Bug brain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 My (six) aching knees . . . . . . . . . . . . . . . . . . . . . . 10 The ants go marching . . . . . . . . . . . . . . . . . . . . . . 12 Foreign invasion . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Snorkeling in the rain . . . . . . . . . . . . . . . . . . . . . . 14 Sunny honey . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Working stiff . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 The bees and the birds . . . . . . . . . . . . . . . . . . . . . 18 Twinkle, twinkle, little bug . . . . . . . . . . . . . . . . . . . 19 Body tunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 2
Amazing animals . . . . . . . . . . . . . . . . . . . . . 23 Reptile Romeos . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Desert dwellers . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Just hangin’ around . . . . . . . . . . . . . . . . . . . . . . . 26 Phobic pachyderm? . . . . . . . . . . . . . . . . . . . . . . . 26 Classy choreography. . . . . . . . . . . . . . . . . . . . . . . 27 It’s all a blur. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Air traffic control. . . . . . . . . . . . . . . . . . . . . . . . . . 30 Mama marsupial . . . . . . . . . . . . . . . . . . . . . . . . . 32 Escargot explorer . . . . . . . . . . . . . . . . . . . . . . . . . 32 All in the family . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Shut-eye for Moby. . . . . . . . . . . . . . . . . . . . . . . . . 34 Fish tales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
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Fish-icles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Condor kissing cousins. . . . . . . . . . . . . . . . . . . . . 37 Long-term companions . . . . . . . . . . . . . . . . . . . . . 38 Tears of a hound . . . . . . . . . . . . . . . . . . . . . . . . . 39 Sorry, Snoopy. . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Strange bedfellows. . . . . . . . . . . . . . . . . . . . . . . . 42 Same or different? . . . . . . . . . . . . . . . . . . . . . . . . 43 Ancient alphabet . . . . . . . . . . . . . . . . . . . . . . . . . 44 Bad behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Leaping lemmings . . . . . . . . . . . . . . . . . . . . . . . . 47 Sink like a stone . . . . . . . . . . . . . . . . . . . . . . . . . 48 Master of disguise . . . . . . . . . . . . . . . . . . . . . . . . 50 Elementary, my dear Watson . . . . . . . . . . . . . . . . . 51
Chapter 3
Vitally vegetal . . . . . . . . . . . . . . . . . . . . . . . 53 It’s easy being green. . . . . . . . . . . . . . . . . . . . . . . 53 Freeloading flora . . . . . . . . . . . . . . . . . . . . . . . . . 54 Kingdom of their own . . . . . . . . . . . . . . . . . . . . . . 56 Seedless seeds . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Fried green tomatoes . . . . . . . . . . . . . . . . . . . . . . 58 Sweet autumn color . . . . . . . . . . . . . . . . . . . . . . . 59 Water threads . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Brains over brawn. . . . . . . . . . . . . . . . . . . . . . . . . 61 Roses are red . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Tricking trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Violets are blue . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Luck of the Irish . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Would you like genes with that?. . . . . . . . . . . . . . . 67 Hot coral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Cold coral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Festive fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Wind in the willows. . . . . . . . . . . . . . . . . . . . . . . . 71 Long-life fruit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Chapter 4
Funky phenomena . . . . . . . . . . . . . . . . . . . . 75 Green eggs and ham . . . . . . . . . . . . . . . . . . . . . . 75 Just like Mama made . . . . . . . . . . . . . . . . . . . . . . 75 A girl’s best friend . . . . . . . . . . . . . . . . . . . . . . . . 76 Hot stones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Metal eater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Wet weave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Fade away . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
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Bleach blonde . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Bubble geometry . . . . . . . . . . . . . . . . . . . . . . . . . 81 Pure as rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Don’t lick the railing in winter . . . . . . . . . . . . . . . . 82 Icebox paradox. . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Ice pimples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Crystal triggers. . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Hoar and rime . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Comfy abode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Couch potato amusements . . . . . . . . . . . . . . . . . . 88 Atomic dance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Auto ambience . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Bad hair day . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Boing, boing, boing . . . . . . . . . . . . . . . . . . . . . . . . 91 Ole timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Ultimate speed . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Stranger than science fiction. . . . . . . . . . . . . . . . . 94 Universal ingredients . . . . . . . . . . . . . . . . . . . . . . 95 Feeling empty. . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Chapter 5
Environmental effects . . . . . . . . . . . . . . . . . 97 Tempest tech . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Eye of the storm. . . . . . . . . . . . . . . . . . . . . . . . . . 98 What’s in a name? . . . . . . . . . . . . . . . . . . . . . . . . 99 Oz inspired . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Rain terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Blowin’ in the wind . . . . . . . . . . . . . . . . . . . . . . . 103 Turn, turn, turn . . . . . . . . . . . . . . . . . . . . . . . . . . 105 Be still, rubber ducky . . . . . . . . . . . . . . . . . . . . . 106 Parched . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Or deluged? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Fast fashion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 Trash or treasure? . . . . . . . . . . . . . . . . . . . . . . . 111 BYO bag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Trash tour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Entertainment budget . . . . . . . . . . . . . . . . . . . . . 115 Vampire appliances . . . . . . . . . . . . . . . . . . . . . . 116 Light pollution . . . . . . . . . . . . . . . . . . . . . . . . . . 116 The big chill . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 The little chill . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Capricious cycles . . . . . . . . . . . . . . . . . . . . . . . . 119
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For good measure . . . . . . . . . . . . . . . . . . . . . . . 121 The case of the missing oxygen. . . . . . . . . . . . . . 122 Under pressure . . . . . . . . . . . . . . . . . . . . . . . . . 123 Nature burps? . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Cause or effect? . . . . . . . . . . . . . . . . . . . . . . . . 125 Back to the drawing board. . . . . . . . . . . . . . . . . . 126
Chapter 6
Home planet . . . . . . . . . . . . . . . . . . . . . . . 129 Continents set sail . . . . . . . . . . . . . . . . . . . . . . . 129 The abyss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Tiny tides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Raisin planet . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Volcanic variety show . . . . . . . . . . . . . . . . . . . . . 132 Serpentine smoldering . . . . . . . . . . . . . . . . . . . . 134 From swamp to SUV . . . . . . . . . . . . . . . . . . . . . . 135 No smoking crater? . . . . . . . . . . . . . . . . . . . . . . 136 Superseded scale . . . . . . . . . . . . . . . . . . . . . . . 137 Doin’ the wave . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Shake, rattle, and roll . . . . . . . . . . . . . . . . . . . . . 139 Pugilistic plates . . . . . . . . . . . . . . . . . . . . . . . . . 140 Redrawing the map. . . . . . . . . . . . . . . . . . . . . . . 141 Slip slidin’ away . . . . . . . . . . . . . . . . . . . . . . . . . 142 Hot date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Old as the hills. . . . . . . . . . . . . . . . . . . . . . . . . . 144 Planetary heft . . . . . . . . . . . . . . . . . . . . . . . . . . 145 Graceful gravity . . . . . . . . . . . . . . . . . . . . . . . . . 146 Throwing weight around . . . . . . . . . . . . . . . . . . . 147 On the level . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Poolside Pythagoras . . . . . . . . . . . . . . . . . . . . . . 148 Magnetic personality . . . . . . . . . . . . . . . . . . . . . 149 Flipping out . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 A flat-out lie . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Chapter 7
The heavens . . . . . . . . . . . . . . . . . . . . . . . 155 Here comes the sun . . . . . . . . . . . . . . . . . . . . . . 155 Fickle, fickle, local star . . . . . . . . . . . . . . . . . . . . 156 Twilight zone . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 It all adds up . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 As the world turns . . . . . . . . . . . . . . . . . . . . . . . 158 To leap, or not to leap? . . . . . . . . . . . . . . . . . . . . 159 Just counting the days . . . . . . . . . . . . . . . . . . . . 160 ’Tis the season . . . . . . . . . . . . . . . . . . . . . . . . . 162
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Smoke and mirrors. . . . . . . . . . . . . . . . . . . . . . . 163 Elusive pot of gold . . . . . . . . . . . . . . . . . . . . . . . 164 Over yonder . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Details, details. . . . . . . . . . . . . . . . . . . . . . . . . . 167 Clouds’ illusions . . . . . . . . . . . . . . . . . . . . . . . . 167 Dust at dusk . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Green flash with envy . . . . . . . . . . . . . . . . . . . . . 169 Moon moniker . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Pink Floyd’s fib . . . . . . . . . . . . . . . . . . . . . . . . . . 171 When the moon hits your eye . . . . . . . . . . . . . . . 172 It’s just a phase . . . . . . . . . . . . . . . . . . . . . . . . . 173 Conspiracy claims . . . . . . . . . . . . . . . . . . . . . . . 174 Moon mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 Lost Luna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Chapter 8
Far out . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Deep impact . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Comet hangout . . . . . . . . . . . . . . . . . . . . . . . . . 180 Comet lifespan. . . . . . . . . . . . . . . . . . . . . . . . . . 180 Messages from little green men? . . . . . . . . . . . . 181 Voyage into eternity . . . . . . . . . . . . . . . . . . . . . . 182 From a distance . . . . . . . . . . . . . . . . . . . . . . . . . 183 In the red. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 Revealing rays . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Hearing the beginning. . . . . . . . . . . . . . . . . . . . . 186 Zooming along . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Star light, quasar bright . . . . . . . . . . . . . . . . . . . 187 Phantom force . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Middle universe . . . . . . . . . . . . . . . . . . . . . . . . . 188 Warp drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Game of cosmic twister . . . . . . . . . . . . . . . . . . . 190 Extraterrestrials dig “The King” . . . . . . . . . . . . . . 191 The stork brought it . . . . . . . . . . . . . . . . . . . . . . 191 Tock tick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Galileo’s legacy . . . . . . . . . . . . . . . . . . . . . . . . . 193 Einstein didn’t lie . . . . . . . . . . . . . . . . . . . . . . . . 195 Light light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 Want stars with that? . . . . . . . . . . . . . . . . . . . . . 196 Supersize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Cute little—ahhhhh! . . . . . . . . . . . . . . . . . . . . . . 197 Wimp? Says who? . . . . . . . . . . . . . . . . . . . . . . . 198
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Solar system synchrony . . . . . . . . . . . . . . . . . . . 199 Analogy anomaly . . . . . . . . . . . . . . . . . . . . . . . . 201 Death by fire . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 The end—not! . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
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Acknowledgments I am tremendously grateful for my wonderful agent, Jodie Rhodes; the vision and hard work of the FT Press Science team; and everyone responsible for the “Quest” section of the San Diego Union-Tribune, especially my four editors: Leigh Fenly, Margaret King, Scott LaFee, and John Cannon. Of course, Curious Folks Ask 2 would not have been possible without the curious folks who asked the questions that have taught me so much over the years. Now matter how quickly the days pass or how busy they seem to be, may we will all find time each day to wonder.
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About the Author Sherry Seethaler is a science writer and educator at the University of California, San Diego. She also writes a weekly column for the San Diego Union-Tribune in which she answers readers’ questions spanning nearly every imaginable science topic. She earned a Bachelor of Science in biochemistry and chemistry from the University of Toronto, a Master of Science and a Master of Philosophy in biology from Yale University, and a Doctor of Philosophy in science and mathematics education from the University of California, Berkeley. She is also the author of Lies, Damned Lies, and Science (FT Press Science, 2009). It serves as a guide and set of tools for making sense of the health- and science-related issues we encounter in our daily lives. A previous anthology of her columns, Curious Folks Ask: 162 Real Answers on Amazing Inventions, Fascinating Products, and Medical Mysteries (FT Press Science, 2010), explores the mysteries of humans and our creations.
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Preface The poster for the movie Cane Toads: An Unnatural History shows a grinning young girl holding up her enormous and, to put it mildly, not especially aesthetically pleasing pet toad. I don’t know what it is with girls and toads, but when I was about the same age as Cane Toad girl, I tried to adopt a toad. My parents stymied the adoption, claiming I’d get warts. So far, no one has written to my science Q&A column in the San Diego Union-Tribune to ask about the putative link between warts and toads, but just for the record, toads don’t cause warts. Their rough, wartlike skin is an adaptation to protect them against the elements. It may also be a failed adaptation to stop little girls from dressing toads in dolls’ clothes. Young minds have an insatiable curiosity about the world. Most of us don’t remember our own “why phase,” but we can recall those moments when, in retrospect, our curiosity seems a little off-color, or even dangerous. For instance, I didn’t really believe that kissing a frog would turn it into a prince, but I still felt the need to do the experiment. Conclusion: Unfortunately, no prince. Fortunately, no salmonella. Reptiles were just as intriguing as amphibians to curious young me. Snake handling seemed like a reasonable way to understand these misunderstood creatures (only nonvenomous ones, of course). Conclusion: Snake poo smells very, very bad and is difficult to wipe off your hands. Looking at things under a microscope sounds benign compared to running with wild things. Then again, that depends on what one puts under the microscope. Say...um... let’s call them nasal samples. Conclusion: Everything looks cool under a microscope, but if you tell anyone, they will pretend to think you are highly uncivilized for extracting the sample in your quest for scientific knowledge. The parents of children who grow up in the Great White North feel the need to pass along this piece of advice: “When it’s freezing outside, don’t put your tongue on anything metal.” I can’t imagine I would have ever thought to lick a frozen railing if my parents hadn’t piqued my curiosity. Conclusion: Ow. ’ongue ’ill ’ick oo ’ozen ’ailing.
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Curiosity isn’t just for kids. Inquiring minds of all ages write in to my science question-and-answer column seeking explanations for life’s mysteries.
• • • • • • • • • • • • • • • • • •
Do spiders dream? Why do lizards do pushups? How do animals change color to match their surroundings? What’s that substance that accumulates in the corners of some dogs’ eyes? How is seedless fruit possible? Why aren’t there any blue roses? Why does the outside of the yolk of hard-boiled eggs turn green? Why does hot water freeze faster than cold? What causes tornadoes? Is the burning of fossil fuels changing the amount of oxygen in the atmosphere? Will another ocean ever form? Why do some volcanoes explode much more violently than others? Is Earth lighter or heavier than it was 50 years ago? What forms stationary clouds over mountain peaks? Could we get along okay if the moon wasn’t there? Is time less understood than gravity? With a powerful enough telescope, could we see the beginning of the universe? What could be beyond our universe?
These are just 18 of the 188 questions that appear in Curious Folks 2: 188 Real Answers on Our Fellow Creatures, Our Planet, and Beyond. The anthology includes questions and answers about all aspects of the world around us, including our fellow creatures big and small, strange everyday phenomena, the natural systems that drive weather and climate, human impacts, the forces that shape our home planet, the enigmas in the sky, and the mysteries of our solar system and beyond. Each Q&A stands alone, and the Q&As can be read in any order, savored a little at a time, or devoured. Within each chapter, the topics are arranged thematically. The whole becomes greater than the sum of parts
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as the Q&As cover significant ground in astronomy, geology, physics, atmospheric and environmental sciences, animal biology, and more, in a way that puts the real world front and center. The answers explore what science knows and what is still in the realm of the unknown—mysteries that perhaps today’s budding scientists will one day solve. The book is divided into eight themes.
• Chapter 1, “Creepy crawlies”—Sometimes they bug us, but insects and spiders have fascinating adaptations that allow them to eke out their existence. Arachnid athletes, ant architects, brainy bees, brisk butterflies, and cellist crickets are among those deserving a critter talent award. • Chapter 2, “Amazing animals”—Animals inspire our admiration and our imagination, often in the form of widespread myths. Separate fact from fiction about suicidal lemmings, elephant fears, dogs’ saliva, mules’ sterility, flocking birds, camels’ humps, and more. • Chapter 3, “Vitally vegetal”—Early classification systems divided living organisms into the animate and the inanimate. Plants, lichens, fungi and coral, and other seemingly inanimate multicellular organisms are now split among three kingdoms, and the secrets beneath their quiet veneers are coming to light. • Chapter 4, “Funky phenomena”—Stuff happens. Strange stuff. And curious folks want to know why. This chapter is a collection of questions about everyday oddities, from mealtime mysteries to agitated atoms and flummoxing forces. • Chapter 5, “Environmental effects”—Nature unleashes her fury upon us in the form of powerful winds, deluges, droughts, and ice ages. Folks want to know how weather and climate are controlled and how to be good stewards of our blue marble. • Chapter 6, “Home planet”—Earth’s atmosphere isn’t the only aspect of the planet that keeps us guessing—the planet’s surface and its depths are also very dynamic. Those of us who live near active faults get constant reminders that geology is relevant to our lives, but earthquakes are just one of the planet’s plethora of puzzles. • Chapter 7, “The heavens”—Humans have always pondered the sky. Even in today’s electronics-obsessed civilization, people seem to find the time to look up from their texting and wonder about what they observe.
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• Chapter 8, “Far out”—Earthlings no longer have to rely on what their eyes can see to study the universe. Powerful telescopes; the ability to detect signals across the electromagnetic spectrum, from radio waves to gamma waves; space missions; and computational modeling are deepening our understanding of the great beyond. This volume of questions about our fellow creatures and the world and universe around us stands alone, but a complementary volume focuses on humans and our creations. Curious Folks Ask: 162 Real Answers on Amazing Inventions, Fascinating Products, and Medical Mysteries is divided into a different eight themes: Ingenious Inventions; Chemical Concoctions; Body Parts; Bodily Functions; Pesky Pathogens; Assorted Ailments; Uniquely Human; and Health Nuts. The 16 science themes in the two books encompass 6 years of question-and-answer columns, a total of 350 questions asked by curious folks. Since I have been writing my weekly science Q&A column, I have learned something new every week. Questions range from things I would never have thought to ask, to those about which I think I know the answer but that always become richer and more intriguing as soon as I start digging deeper. I do not answer the questions off the top of my head without researching the answer. Whenever possible, I carefully search the primary, peer-reviewed scientific literature for new findings and a wider range of viewpoints. Because science is constantly changing and because it advances one small piece at a time, researching the columns is a lot like sleuthing. Each column is its own story, which I hope you will find both satisfying and enticing. Curiosity begets more curiosity. That is why science is such a magnificent endeavor. The more we learn about particles, forces, cells, genetics and development, ecosystems, atmospheric processes, planetary dynamics, and the vast expanse beyond our solar system, the more magical and beautiful it all becomes. So keep wondering, keep asking, and be extra kind to toads in pink tutus.
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1 Creepy crawlies Eight-legged epicure Do some spiders trap and feed on mosquitoes? Considering that the female mosquito, after feeding, would be a great source of protein, it would seem a good target. Or have mosquitoes evolved an evasive technique for spider webs? Just as we humans have individual, sometimes unusual, tastes— such as liverwurst, Jell-O with shredded carrots, and stinky cheeses— our eight-legged friends have theirs. Although spiders mostly dine on whatever potential prey comes their way, some spiders find mosquitoes particularly pleasing to the palate. One species, a jumping spider from East Africa, seems to have a special preference for female mosquitoes that have had a recent blood meal. In laboratory studies, the spiders consistently choose blood-fed mosquitoes over sugar-fed ones. In doing so, the spiders feed indirectly on blood from vertebrates. No spiders are known to feed directly on vertebrate blood because they lack the necessary specialized mouthparts. When a female mosquito gorges on blood, her mass may increase more than 200 percent. The increase in mass makes the mosquito slower and less agile, and, therefore, an easier target for predators. East African jumping spiders do not pursue blood-fed mosquitoes simply because they learn that full mosquitoes are easier to catch. The preference is instinctive. Even captive spiders that had no prior experience with mosquitoes prefer the smell of blood-fed mosquitoes.
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Juvenile East African jumping spiders prefer mosquitoes from the genus Anopheles, the type of mosquito that carries the parasite that causes malaria. Anopheles mosquitoes have a distinctive resting posture, with their hind legs raised and their abdomen angled upward at 45° to the surface on which they are standing. Other species rest parallel to the surface. Anopheles mosquitoes’ posture makes them vulnerable to attack by the young jumping spiders, which sneak up behind the mosquitoes, crawl under them, and grab them from beneath. The tactic allows a young spider to overpower a mosquito many times its size. Another type of spider, found in Thailand and of interest because it attacks a species of mosquito known to carry the virus that causes Dengue fever, is less of a wrestler and more of a cowboy. It captures mosquitoes by lassoing them with a strand of silk that it throws with its hind legs. Spiders around the world eat mosquitoes. Spiders do not have to be cowboys or wrestlers to nab mosquitoes, though. They can also catch them the old-fashioned way, because mosquitoes do get caught in webs.
Fancy footwork Do spiders ever get tangled up in their own webs or in other spiders’ webs?
A few clever adaptations generally prevent spiders from becoming ensnared in their webs. Spiders that make sticky webs leave some strands, often the radial strands, glue free. When maneuvering around their own webs, spiders tread carefully, differentiating between sticky and nonsticky threads. Claws and spines on the feet of spiders also make it easier for them to move around the web. They can grip a thread between the claw and spines. Upon release of the claw, the rebound of the spines pushes the thread away from the foot. This facilitates release of the thread even if the spider happens to grab one of the sticky ones. For some spiders, a fluid excreted through hollow hairs on the legs may also offer some stick prevention. Download at www.wowebook.com
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Even if a gust of wind tosses a spider onto the sticky strands of its own web, it can work itself free. Insects can sometimes escape from a web if they have enough time. For example, green lacewings tug and cut strands of the web until they have freed everything but their wings. Their hair-covered wings don’t stick to the web very well, and eventually the insect falls free, but only if the spider doesn’t get to it first. Spiders have no qualms about eating each other. If a spider is unlucky enough to get stuck in the web of a larger spider, it will likely end up as dinner. A male spider courting a lady spider doesn’t even need to get caught in her web to find himself the main course.
Silk architecture How can a spider make a web 20 feet apart from pole to pole? The most difficult part of building the web is the first strand, which forms a bridge between the two poles. The spider makes the bridge by releasing a length of sticky thread and kiting—letting the thread blow in the breeze. With a bit of luck, it will catch on another object. When the spider feels the thread catch onto something, it pulls it tight and attaches it to the starting point. Next the spider walks the high wire, using special claws to grip the thread. As the spider does so, it releases a slack thread beneath the bridge thread. With the slack thread attached to the other side, the spider usually climbs back to the middle of it, lowers itself, and attaches the thread to some object to form a Y-shape. This strategy does not work between the poles, so the spider has to attach it to a spot lower on the pole, either by kiting or by climbing down the pole. When the difficult main support structure of the web is in place, the spider can complete the frame, add radius threads from the frame to the center of the web, and create a spiral from the center to the frame.
Let sleeping spiders lie Do spiders sleep—perhaps dream?
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“To sleep, perchance to dream,” pondered Shakespeare’s Hamlet in his famous “To be or not to be” soliloquy. He was contemplating what happens after people die, but sleep researchers get equally ponderous about why we need sleep and whether sleep and dreaming are universal across the animal kingdom. Even single-celled organisms have a circadian rhythm, a daily pattern of activity and inactivity. Spiders do, too. Some spiders are active during the day and inactive at night, and others are active at night and quiescent during the day. Of course, an inactive spider is not necessarily asleep. Sleep is defined as a period of inactivity with reduced responsiveness to sensory information that is rapidly reversible (unlike hibernation or a coma). To be considered sleep, the rest period must also be homeostatically regulated—that is, disrupting it creates an increased need for sleep. No published studies have measured changes in spiders’ behavior when their rest period is disrupted to determine whether it meets the strict definition of sleep. Anecdotes from tarantula owners that their pets are sometimes difficult to rouse suggest that they sleep. Laboratory studies on fruit flies also support the notion that spiders sleep (or, at least, that invertebrates sleep). Fruit flies have periods of inactivity in which they are unresponsive to small vibrations that would ordinarily make them respond. During the inactive state, gentle tapping on their container disturbs them. If they’re deprived of a night’s rest this way, they compensate by resting more the next day. Not only does their behavior fit the definition of sleep, but it also bears similarities to sleep in mammals. Young fruit flies need more sleep than older fruit flies, and sleep is more fragmented in older flies. Mutant insomniac flies exist. In addition, caffeine, antihistamines, and amphetamines have similar effects on sleep and waking in flies as they do in mammals. As appears to be the case in mammals, the activity of about 1 percent of genes in flies is different during sleep than during wakefulness. Researchers are not particularly interested in drowsy fruit flies. They are using fruit flies as a tool to understand the genetic and biochemical mechanisms that control sleep, with the goal of developing ways to treat sleep disorders in people.
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No one knows whether fruit flies and spiders dream of each other, or anything else. The scientific literature does not contain any reports of invertebrate rapid eye movement (REM) sleep—the type associated with dreaming.
Lazarus fly I found a dead fly in my refrigerator (days unknown) and threw it in the sink. A few minutes later, it flew away. How is this possible? Can a fly live in the refrigerator? How long do flies live? It was not dead, just in a cold-induced stupor. In northerly climates, it is not unusual to see cluster flies literally crawling out of the woodwork on the first warm day after a cold spell. The flies are quite slow until they warm up. If you had not rescued your fly, it would have eventually died because it was too cold to move, eat, or drink. Different species of flies have different life spans. Flies’ life spans also depend on temperature; for example, their life cycle is quicker at 85°F than at 65°F. Researchers have identified specific genes in fruit flies that play a role in longevity. For example, one such gene is called methuselah; another is I’m not dead yet. (Who said scientists take themselves too seriously?) Mutations in these genes can double the approximately month-long life of the fly. Research on fly longevity is not aimed at making wise old flies, but instead at understanding the mechanisms of the aging process in flies and humans.
Mile-high club How high can a common housefly fly? How high can a mosquito fly? Does the answer depend on the elevation at ground level, or would the answer be the same in Denver as it is in San Diego?
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A zone about 25 feet above Earth’s surface (depending on atmospheric conditions and species of insect) is known as the flight boundary layer, where wind speed is equivalent to maximum insect flight speed. Because wind speed increases with height, an insect needs to hang out below the flight boundary layer if it wants to be able to fly in any direction in its quest for food, a mate, or shelter. Nonetheless, insects are commonly found at much greater heights. Mosquitoes have been collected at 1,000 feet. Houseflies can probably get that high, too. Migrating insects such as locusts and butterflies ascend much higher. Ground-based radar has detected insects nearly 2 miles above the surface. At these heights, insects can maneuver, but the wind is too strong for them to travel upwind. For example, this explains why plagues of locusts lasting several years tend to spread according to the direction of the prevailing winds. Insects cannot fly if the air is too cold. Temperature decreases with altitude, but in a temperature inversion, a layer of warm air sits atop cooler, denser air. Temperature measurements with kites have shown that migrating insects concentrate in the warm air at the top of temperature inversions. An exception is passive migrators, including tiny moth larvae and tiny spiders (albeit not insects) that don’t need to flap their wings to stay aloft. They migrate on silk threads and can be lifted to great heights by updrafts of air and carried long distances. They are deposited when winds change, or heavy rainfall can wash them out. Topography—features of a particular area of land—influences movements and layering of air in the lower atmosphere. Therefore, mountain ranges can alter insect flight. Air on the upwind side of a mountain is forced to ascend, creating an updraft that migrating butterflies take advantage of to gain height by gliding in circles. Because elevation influences average temperatures, it also determines what species live in a particular area. In the past, mountain ranges have limited the spread of diseases carried by insects. But this seems to be changing as annual temperatures rise. For example, mosquito-borne diseases such as malaria and Dengue fever are being reported at increasing elevations in Asia, Africa, and Central and South America.
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Colorful compass clocks How do monarch butterflies migrate and navigate such great distances? North America has two migratory populations of monarch butterflies. One breeds west of the Rocky Mountains and overwinters in forested areas along the coast of California. A much larger population breeds east of the Rockies and migrates up to 2,500 miles (4,000 km) from southern Canada to overwintering sites in mountain forests near Mexico City. As autumn approaches, decreasing daylight triggers hormonal changes in monarchs that lead to reproductive diapause, the cessation of mating behavior. In addition to their overwhelming urge to fly south, migrants have greater fat stores, enhanced cold tolerance, and increased longevity. Migrating monarchs appear to use tail winds to conserve energy and reduce wing wear. At their overwintering sites, monarchs are mostly quiescent but occasionally leave their roosts to drink water from dewy fields and streams nearby. Around spring equinox, monarchs begin the journey northward from overwintering sites. They breed and lay eggs on newly emerged milkweed in the southern part of the United States, and then they die. As milkweed returns to the northernmost portions of the breeding range, adults of the new generation finish the journey their parents started. During the summer, two or more short-lived generations are produced. Because the populations that migrate in the autumn are three to five generations removed from those that occupied the overwintering sites the previous year, the fidelity with which monarchs return to the sites is remarkable. It also indicates that migration is genetic instead of learned. Monarchs have a time-compensated sun compass—they use the sun to determine their flight orientation and have an internal clock that allows them to maintain their flight orientation in a south or southwest direction as the sun moves across the sky during the day.
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Researchers have demonstrated the time compensation of the sun compass by shifting migratory monarchs’ day and night cycle in the laboratory and then exposing them to sunlight. Jet-lagged butterflies flew in the wrong direction. The day and night cycle sets the monarchs’ internal clocks. The clocks themselves have “molecular gears”—several genes that interact to switch each other on and off in a cyclic manner. Scientists initially identified four cells in monarchs’ central brain as the clock, but a recent study found that monarchs also have clocks in their antennae. The compass portion of the time-compensated sun compass consists of cells in the eye that respond to ultraviolet light. Scientists are still researching how the monarchs’ compass and clocks interact, as well as how monarchs may use Earth’s magnetic field to guide them on their incredible journey.
Reinventing oneself Does an insect undergoing the three distinct stages of metamorphosis (larva, pupa, adult) retain the identical DNA profile? And does the DNA profile vary among individuals? The dramatic remodeling of an insect’s body that transforms a crawling, food-minded larva into a walking, flying, reproducing adult is not the result of changes in the insect’s DNA. Similar to us, each insect has a unique DNA profile and the cells in its various organs share the same genetic blueprint. Specialized cells differ in which genes are switched on and, therefore, what proteins are produced. An egg cell contains a concentration gradient of signaling molecules that assigns the initial pattern of cell identities in an embryo. Throughout development, a plethora of chemical signals prompts genes to switch on and off. Two hormones, juvenile hormone and ecdysone, are the master signals for insect metamorphosis. A larva morphs into an adult in response to declining levels of juvenile hormone and simultaneous spikes in ecdysone. The hormonal changes cause some larval cells to die and also lead to the production of new cells and the repurposing of other cells. Download at www.wowebook.com
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Among the cells that die during metamorphosis are the larval muscles. Adult muscles use remnants of the larval muscle fibers, but mostly they develop from cells in imaginal disks—hollow sacs of unspecialized cells that form in the embryo and remain throughout larval life. Flight muscles can constitute more than 10 percent of an adult insect’s mass and contract about 60 times faster than the larval muscles; they also differ in protein content. Most larval sensory nerves die and are replaced, but motor neurons—the nerves that move the muscles—are reused. The larval motor neurons retract their branches as the larval muscles die, and serve as templates for the developing adult muscles before growing new branches to them. Economizing by recycling instead of disposing of larval cells also occurs in the central nervous system. Although larval and adult behaviors are divergent, some behaviors survive metamorphosis. One study showed that a moth can remember what it learned as a caterpillar. Caterpillars that were exposed to an odor paired with a small shock learned to avoid the odor and continued to avoid it as adults, whereas untrained caterpillars did not. Only holometabolous insects—including butterflies, beetles, bees, and flies—go through complete metamorphosis. Hemimetabolous insects—including cockroaches, grasshoppers, crickets, and dragonflies—do not have a larval stage. They hatch as mini adults that lack wings and reproductive organs. The benefit of being holometabolous is that larvae and adult insects can exploit different habitats and food sources.
Bug brain Do insects have brains (actual brains, as we know them)? If so, how big is a flea brain or an ant brain? If they don’t have brains, how do they “think”? Insects have brains. They may bug us, but insects are capable of complex behaviors and can even learn. For example, leaf-cutting ants collect leaves and use them to farm fungus for food. Honeybees dance to communicate the location of a food source to hivemates.
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Fruit flies learn to avoid an odor when scientists have previously paired it with an electric shock. Insect brains are as large as 7.5 millimeters (mm), about onethird of an inch, in diameter. An ant brain is around 0.15mm in diameter but contains some 250,000 nerve cells. A housefly’s brain weighs less than half a milligram (about the mass of a fine grain of sand) and has around 350,000 nerve cells. Based on their relative behavioral sophistication, I would estimate that fleas have smaller, less complex brains than ants and flies. At the other end of the scale, a bee’s brain contains about 850,000 nerve cells. The human brain has an estimated 100 billion nerve cells. Two predominant features of the insect brain are optic lobes and mushroom bodies. The optic lobes contain about three-quarters of the nerve cells in a fly’s brain. They join the compound eyes and are responsible for filtering and integrating visual information. The mushroom bodies—so called because of their shape—synthesize sensory information, particularly chemical signals, and are largest in bees and other insects with a keen sense of smell. The mushroom bodies may also play a role in memory formation. For example, blocking nerve activity in bees’ mushroom bodies with a thin, cold needle prevents bees from learning the association between a novel odor and food.
My (six) aching knees Do insects experience pain if you mistreat them? Will they know pain in any way relative to a human’s experience of pain? Two scientific papers summarize the lack of consensus on this matter. One claims that invertebrate organisms do not experience pain (Nature, September 13, 2001). The other states that invertebrates might suffer the same way as vertebrates (Animal Welfare, February 2001). Insects and other invertebrates certainly can detect noxious things in their environments. For example, they withdraw from toxic
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chemicals and hot surfaces, and they attempt to escape mechanical compression. Avoidance or escape behavior could indicate that an insect is in pain. On the other hand, insects also attempt to escape from non-noxious things, such as gentle touch or a sudden change in illumination. Recent studies on fruit fly larvae show that they detect noxious and non-noxious things in fundamentally different ways. A light touch usually causes larvae to halt and reverse slightly, but larvae touched with a heated probe launch into a sideways roll. Unlike these gymnastically gifted maggots, researchers have discovered mutants, dubbed painless, that respond normally to gentle touch but fail to respond to a heated probe and other harms. Painless mutants lack a certain type of protein molecule called a nociceptor that detects noxious heat, chemicals, and pressure. In normal fruit fly larvae, detection of these dangers activates the nerves in which the nociceptors reside. Similar nerves and nociceptors exist in humans. We usually feel pain when they are activated, which suggests that insects can feel pain, too. Because our brains play a significant role in our perception of pain, and insects’ brains are much more rudimentary than ours, their experience is probably different. Our brains do not simply act as “pain-o-meters” that register the signals coming from the nociceptor-containing nerves in our bodies. Brain-imaging studies show that several different areas of our brains process the incoming signals. For example, activation of regions in the limbic system of the brain influences our subjective, emotional experience of pain. Different regions of the brain’s cortex—the part of the brain involved in higher thinking—also actively process pain signals. In humans, several lines of evidence show that pain is much more than a sensory experience. Our expectations about how bad the pain will be influence how bad it feels. When we think that we have control over pain, it increases our pain tolerance. Our emotional state can influence pain perception. Finally, we may still experience pain even after the nerves that carry the pain-related signals from the body are removed.
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The ants go marching Whenever I observe a line of ants traveling in opposite directions, individual ants always appear to be “touching noses” as they pass one another, as if in communication. Is this really what they are doing? Yes, they are communicating with each other. Ants live in social groups and have developed a highly sophisticated chemical communication system. They leave chemical trails to lead their comrades to a newly discovered food source (to the dismay of picnickers everywhere), release chemical alarm signals to warn of predators, and have a personal chemical “signature” that lets ants know who is a member of their colony. Chemical signals that one animal releases to influence the behavior of another animal, usually of the same species, are known as pheromones. Ants have different types of glands that release pheromones, several of which are in the head of the ant. Ants detect pheromones using their antennae. When ants encounter their nestmates on the trail, they also sometimes offer them liquid food that they can store for long periods without digesting in an expandable sac called a crop. This exchange may excite the ant receiving the food and make it more likely to follow the scent trail.
Foreign invasion Tiny black ants are invading my kitchen. Where do they come from? They seem to like anything sweet. How do I prevent them from appearing on my sink, in my breadbox, and in other places in my house? I’m using Raid wherever I find them and keeping all edibles in the refrigerator. They are Argentine ants, an invasive species native to northern Argentina, Paraguay, and surrounding regions. Their ancestors likely hitched a ride on ships carrying coffee from South America in the late
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1800s, and Argentine ants now reside in many Southern states, including California. According to David Holway, a professor of biology at the University of California, San Diego, Argentine ants like damp soils. In arid regions such as southern California, they would primarily live along creeks and the foggy coast if it weren’t for extensive irrigation. Irrigation has allowed Argentine ants to spread throughout many otherwise inhospitable areas. If you live in a place with low rainfall, try to convince your neighbors to stop watering their lawns and landscape with native plants instead, as that should help your ant problem. When ants have taken up residence in your home, they can be difficult to eradicate. I, too, turned to synthetic pesticides out of desperation the day I woke up and found the ant equivalents of Lewis and Clark exploring my hair. Synthetic pesticides can keep killing ants that walk across the pesticide residue for weeks after you spray. Unfortunately, this also means the people and pets in your household are being exposed to these toxins. Some pesticides are safer for people and pets. For example, ants don’t like to walk through talcum powder because it is like walking through broken glass from their perspective. Powdered boric acid is another effective remedy. Sprinkle it behind appliances or dilute it in water and use as a spray. Commercially available alternative pesticides, such as a mixture of peppermint and soap, also work, albeit mostly to reroute the ants. If you have recurring problems with these ants, try treating the perimeter of your house with pesticides. Spray them right against the foundation, and in places where water pipes come into your house. Sealing cracks in the foundation, around windows, and in similar locations can also help reduce their points of entry. Argentine ants do like sweets, but they are scavengers that also feast on dander, dead insects, and anything else they can get their tiny mandibles around. So they may infest your house even if all your food is in sealed containers. They also collect water, which explains why they often appear in sinks and water fountains, especially in late summer and early fall.
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Snorkeling in the rain Do ants breathe? If so, what happens to them when it rains? Do they drown? Do their breathing apparatuses get flooded, killing them? Ants and most other insects breathe through a complex system of flexible tubes called trachea. Large tracheal tubes branch into successively smaller tubes that extend throughout the body, including the legs and the wings of flying insects. The smallest tubes, tracheoles, are less than a micrometer in diameter (about one-hundredth the size of a human hair), and they exchange gases with the tissues of the body. Because insects lack lungs, scientists previously thought that gas exchange through the trachea was completely passive—that is, the tendency of gases to move from high to low concentration caused oxygen to flow into the body and carbon dioxide to flow out of the body. Insects use passive gas exchange, but they also breathe through an active mechanism, controlled similarly to how an accordion is played, with its switches and bellows. As the switches on an accordion open and close banks of reeds, the insect nervous system switches open and closed spiracles— gateways between the tracheal system and the outside air. The insect “bellows” are the muscles that compress the exoskeleton—an insect’s tough outer casing—which, in turn, puts pressure on the hemolymph—insect blood that fills the body cavity—and causes it to compress the trachea. The muscles attached to an insect’s exoskeleton thus control a cycle of inflation and deflation of the trachea. The capability to open and close spiracles helps protect insects against drowning. A partially submerged insect could selectively open the spiracles not under water. A fully submerged insect could close all its spiracles. Because insect respiratory systems are very efficient, resting insects sometimes stop breathing for a half-hour at a time, so they could wait out a short rain. For longer rains, they would need to take shelter. Underground colonies have an intricate architecture that protects ants from the elements, as revealed by research not for the faint of
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heart. Biologist Walter Tschinkel from Florida State University excavated colonies of Florida harvester ants and made metal and plaster casts of their entire network of shafts and chambers. The largest nests are about 12 feet deep, made by worker ants that had to dig out almost 90 pounds of sand. Young worker ants and the ant brood pack densely into the nest’s lower chambers, where air pockets would be found even when it rained.
Sunny honey Why aren’t bees able to fly at night? It seems if they don’t get back to their hive before dark, or are unable to find a place to hide (such as one of my roses), I find them dead or dying. Is heat or solar radiation needed to make them fly? Temperature drop at sundown is one reason bees get stranded. Their flight muscles must be warm enough to work. Another reason is that foraging and homing are predominantly visual tasks, and bees that are active during the day do not see well in dim light. Day-active insects typically have apposition compound eyes, in which light reaches the photoreceptors—light-detecting cells in the retina—exclusively from the lens located directly above it. In contrast, nocturnal insects, including most moths, typically have superposition compound eyes, in which each photoreceptor receives light from hundreds, sometimes even thousands, of lenses. The light-gathering power of superposition eyes gives them a sensitivity advantage compared to apposition eyes. Surprisingly, although all bees have apposition eyes, several bee species forage at night or during twilight. One species, the giant Indian carpenter bee, has even been observed foraging on moonless nights. Bee species that fly between sunset and sunrise generally live in warm desert areas or in forests in tropical or subtropical regions where the flowers of many plants open only at night. Competition for nectar and predation are often reduced during nocturnal foraging. To overcome the disadvantage of apposition eyes, bees that forage in dim light have various visual adaptations. Some lie within the
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eye itself; others are located in the neural circuitry that processes visual information. For example, the three simple eyes, or ocelli, that bees have on the top of their heads between their compound eyes are considerably larger in these species. Ocelli are thought to be involved in flight control. Each lens within the individual eye units that constitute the compound eyes of night-flying bees is larger relative to body size, and night-flying bees typically have more of these eye units. Their photoreceptors are more light sensitive. Not only are the signals from the photoreceptors sent along the usual visual channels to the brain, but these bees also have specialized nerve cells that sum the outputs of neighboring visual channels. Regarding the mortality you witness among bees that fail to take cover when the light dims and the temperature drops, some bees die from age and injury. Because of the way bee colonies divide tasks, foragers are the hive’s oldest workers, and bees don’t get to retire.
Working stiff I frequently walk the beach and see dozens of bees stranded at the waterline. Most are dead and a few are just barely alive. Is this related to worldwide bee health problems? Does it do any good to move the bees to plants on the cliffs or is my intervention more of a problem than a help? The lifespan of a honeybee is about five to seven weeks. In a healthy colony of around 50,000 bees, an average of 1,000 bees die daily. The bees at the beach are middle aged or elderly. We know this because an age-related division of labor occurs among most social insects. Worker bees nurse the brood and tend to the hive until they are two or three weeks old, and then they begin foraging. Bees literally work themselves to death. If they do not fall victim to one of the many hazards of being a bee, such as predation or disease, they die after wearing out their wings logging hundreds of miles searching for flowers and lugging nectar and pollen back to the hive. Compounding the normal bee mortality is an enigmatic disappearance of bees. In October 2006, U.S. beekeepers began reporting large Download at www.wowebook.com
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losses of bee colonies. Symptoms exhibited by the affected hives did not match those produced by known bee parasites and diseases. The name Colony Collapse Disorder (CCD) was coined to describe the sudden losses, which have since been documented in many other countries. Four main symptoms are associated with hives that have been lost to CCD. First, adult bees are absent. Second, few dead worker bees are found within or surrounding the hive. Third, the brood is still present. Fourth, food stores remain and are not scavenged by bees from other colonies or common colony pests. Of the long list of possible CCD causes, most attention is on three: infectious agents, pesticides, and stresses related to beemanagement practices. The strongest evidence to date, from a recent study of 91 colonies in 13 different apiaries in Florida and California, implicates infectious agents but does not rule out other causes. The study found that CCD colonies had higher levels of viruses and were infected with a greater diversity of viruses than non-CCD colonies. Also, the distribution of CCD colonies was not random. Dead colonies tended to neighbor other dead colonies, suggesting that the condition is contagious. Because bees live in crowded conditions with genetically similar individuals, new diseases and parasites spread quickly. No single disease distinguished CCD and non-CCD colonies in the study. Other studies have found specific diseases—including Nosema ceranae, a fungus that attacks cells in the gut, and Israeli acute paralysis virus—that are more common in collapsing colonies. It is not clear whether the diseases caused the collapse, but one way that bees control spread of disease is to have infected individuals leave the hive. Many factors can reduce bees’ disease resistance. For example, parasitic mites, which feed on bee blood, weaken their hosts and transmit disease. Recently, the mites have been evolving resistance to the most effective chemicals used to control them. In addition, foraging bees are exposed to myriad pesticides intended for other insects. France banned one insecticide thought to be particularly harmful to bees, but colony losses have continued. Beehives are also being trucked greater distances than in the past, typically to less diverse food sources. Bees are often fed pollen substitutes
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and corn syrup in the winter, which may harm their health. The general consensus is that CCD is the result of this perfect storm of factors working in combination. Although most of the workers you observe dying away from the hive are likely the result of normal population turnover, because of the sheer number of bees that involves, some may be from collapsing hives. For example, one of the symptoms of infection with Israeli acute paralysis virus is disorientation. Likewise, certain pesticides have been found to cause learning and memory problems in bees. Disorientation and memory problems could leave bees stranded on the beach. Sea spray is another hazard for bees, especially on cold days. Evaporative cooling chills the bees, and bees need to keep their flight muscles warm to fly. Bees quickly rescued from our swimming pool usually fly off after drying in the sun and shivering to warm their flight muscles. But the rescue attempt fails if the bee is disoriented or injured, or stings its potential rescuer. Beekeepers have long had to contend with “disappearing diseases,” especially after harsh winters. Nonetheless, CCD has created quite a buzz because bee pollination is so important in agriculture, adding an estimated $15 billion in improved quality and yield of U.S. crops annually. The recent declines exacerbate a beekeeping trend that has more than halved the number of U.S. hives to 2.4 million during the past half-century.
The bees and the birds A bottlebrush in my backyard and an agave plant in the canyon have attracted numerous bees and birds. Do the bees ever sting the birds because they are both going after the nectar? The barb of a stinger needs to lodge in an elastic material to pull away from a bee’s bottom and deliver venom. Thick skin and feathers provide birds with protection, but they can still get stung. Honeyguides—small birds in Africa and Asia that feed on beeswax from honeybees—have been found dead under beehives with hundreds of stings.
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Bees are most likely to sting when they are protecting the hive, but some species vigorously defend nectar sources. Quarrels over flowers are most likely to arise when resources are limited. During these disputes, the bully and the bullied have been observed to reverse places. At times, hummingbirds chase bees away from flowers, but at other times, the bees turn around and chase the bird instead of fleeing. One study in the Sierra Nevada discovered that in a meadow where bees were abundant, hummingbirds foraged mainly in the morning and evening, when it was cooler and bees were less active. In a meadow that was devoid of bees, hummingbirds collected nectar all day. Hummingbirds did not show hawkmoths the same respect—the birds chased them away from flowers. The birds and the bees are not all about conflict. More than 100 species of birds, especially in the tropics, have been reported to build their nests close (less than 5 feet) to the nests of bees, wasps, and ants. The birds take advantage of the biting and stinging insects’ defensiveness of their own broods. Predation is the greatest risk to birds’ eggs and nestlings. Building nests in places that are inconspicuous or inaccessible does not always work, especially in regions where terrific climbers are prevalent. So neighboring nests of bees, wasps, and ants help birds up the ante against potential predators. A study in Costa Rica in which wasp nests were relocated close to the nests of wrens showed that the young of wrens nested near wasp nests were more likely to survive than the young of wrens without wasp nests in proximity. The researchers observed the birds’ main predators, monkeys, beating a hasty retreat from attempts to rob the birds’ nests when confronted by the birds’ aggressive insect neighbors. The birds avoided the wasps and were not usually disturbed by them.
Twinkle, twinkle, little bug Why doesn’t California have fireflies as the Midwest does?
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In many parts of the country on warm summer evenings, the sky twinkles with what appear to be flying, flashing light-emitting diodes (LEDs). The little lights are fireflies, or lightning bugs, using an interactive visual Morse code to find that special someone for a brief summer romance. Fireflies are a large family of beetles known as Lampyridae, or lampyrids. More than 2,000 species of fireflies have been identified worldwide, but by some estimates, this is just a quarter of the total number of firefly species. All fireflies produce light at some stage during their life cycle, but not all species put on a nightly light show in search of a mate. In addition to the “lightning bug” fireflies in which both males and females use species-specific light signals to communicate, there are “glowworm” fireflies and “dark” fireflies. Glowworm fireflies have grublike females that emerge from burrows at night and emit a continuous glow. Males seek out the glow but do not signal. Dark fireflies are generally active during the day. Instead of light signals, they use chemicals called pheromones to attract a mate. In California, 18 species of fireflies have been identified, but the Golden State lacks lightning bug fireflies. Why Californians got the short end of the firefly stick is not clear. Predation could have played a role. The modes of communication different species of fireflies use have different advantages and disadvantages. Would-be paramours can more easily localize the source of a light signal than the source of pheromones. But light signals are more vulnerable to espionage by would-be predators because a predator must possess a chemical receptor—detector—for a specific pheromone. Researchers have proposed that in an ancestor of fireflies, bioluminescence—light production—was used solely to deter predators and only later evolved in some species as a tool for finding a mate. The light-producing substance, luciferin, is bitter. Fireflies produce other chemicals that are distasteful and even toxic to some predators. However, other predators have no qualms about snacking on fireflies, so the types of predators in a region should influence what firefly signaling modes (and, hence, what species) are present.
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Climate also influences the distribution of firefly species. The southeastern United States, with its hot, muggy summer nights, has the highest concentration of lightning bug fireflies. In California, typically cool summer nights would be disadvantageous for all but dark fireflies that are active during the day.
Body tunes Why do crickets chirp? Those chirps you hear are usually gentlemen crickets serenading the lady crickets. Males use a loud, monotonous sound to attract a female, and a quick, quieter chirp to court a female nearby. Male crickets also chirp to defend their territory against other male crickets. Crickets make sound through stridulation, rubbing one body part against another. They rub a sharp-edged ridge (the scraper) on the outer edge of one wing against a series of sawlike teeth (the file) on the other wing. As when a bow is pulled across the strings of a violin, the scraper dragging across the file sets up a vibration. The vibration is amplified as it resonates on the wing membrane. Each species of cricket has its own song, but the song also varies within a population. A male’s song is revealing. Larger males have a song with a lower carrier frequency, or pitch. Females seem to be able to determine the relative size of a male cricket from his song because they find lower pitch songs more attractive. Temperature affects crickets’ chirp rates. The Old Farmer’s Almanac provides a formula to convert the chirp rate to temperature. To get the temperature in Fahrenheit, count the number of chirps in 14 seconds and add 40. It may not be as accurate as a thermometer, but if the crickets stop chirping, grab a jacket.
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2 Amazing animals Reptile Romeos We live in a home surrounded by a plethora of lizards. In observing them, I began to wonder, why do they do “pushups” while sunning themselves? They are displaying athletic flamboyance like their human counterparts at Venice Beach. Depending on the nuances, lizard pushups may convey “I’m too tough to mess with” or “Hey, ladies, check me out.” Body language is a rich form of communication for lizard jocks and jockettes. Other lizards can glean useful information from the unique characteristics of the pushups: overall body posture, pattern of head bobs, and how the legs stretch and flex. For example, the number of pushups performed by a male in a territorial interaction corresponds with his aggressiveness and pugilistic prowess. Therefore, a potential opponent can avoid a fight he has little chance of winning. Lizard species have distinct pushup styles, and within a species, regional differences in pushup dialects often arise. Some scientists speculate that new species may emerge when regional pushup dialects diverge so much that males and females do not understand each other and courtship fails. Individual lizards also have their own unique pushup flair. Even after scientists tuckered out lizards by making them run on a treadmill, their pushups maintained a reliable individual pattern. Pushup styles have important ramifications for social behavior and kin recognition. For example, at territorial boundaries, lizards usually 23
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tolerate their neighbors, but not strangers. A lizard would waste energy if he harassed his neighbor every time he headed out to make his rounds, but he may need to put a new guy in town in his place. Both male and female lizards do pushups in a variety of contexts, such as when encountering another lizard, when encountering chemical markings left by another lizard, or after moving from one location to another. Lizards may broadcast their presence whether or not other lizards are nearby. Pushups and head bobbing may also play a role in vision. Humans and other animals with frontal eyes can determine the distance to an object by interpreting the slightly different projection of it onto each retina. With eyes on the sides of their heads, lizards have a panoramic view of the horizon. The arrangement is handy for spotting predators approaching from any direction, but it does not permit binocular vision. Just as driving in a car makes nearby objects appear to move more quickly than distant objects, rapid motion of a lizard’s head reveals the relative distance of objects. Birds and other animals with widely spaced eyes also move their heads to gauge depth.
Desert dwellers How can camels go so long without drinking water?
Many of us remember being told as kids that camels store water in their humps. Backpackers will be familiar with Camel Baks or dromedaries (so-called for the one-humped Arabian camel, Camelus dromedarius) for carrying water. The hump actually is made of fat, which helps a camel survive for long periods without food. Camels do not store water. Two sets of adaptations give camels their ability to survive for long periods (weeks) without drinking: 1) extremely efficient water conservation and 2) excellent dehydration tolerance. Most mammals, including humans, need to keep their body temperatures relatively constant and cool down via evaporation of water by sweating or panting. Camels can allow their body temperatures to Download at www.wowebook.com
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rise by more than 10° Fahrenheit (6° Celsius) on hot days, which reduces the need for sweating. Adaptations of the digestive tract and kidneys permit the camel to produce very dry feces and highly concentrated urine. Although other animals respond to dehydration by excreting less water in their waste products, few can do it as effectively as camels. In addition, the tough mouth of a camel allows it to eat thorny desert vegetation, which often has significant water content. Because of these adaptations, camels dehydrate more slowly than other animals. But camels can also survive losses of up to one-third of their body weight in water, twice the level of dehydration that would kill a horse. When presented with water, camels rehydrate remarkably quickly, within a matter of minutes. Adaptations of camels’ blood facilitate dehydration tolerance and the ability to rehydrate quickly. Most animals lose a significant proportion of water from the blood when dehydrated. The blood becomes thicker and more difficult to pump through small blood vessels in the skin, where heat can be released to the environment. Fatal overheating can result. In camels, water loss from the blood is reduced by the presence of a high level of a protein called albumin, which attracts water. When dehydrated, a camel loses most of its water from the digestive tract, which contains large quantities of liquid in an animal like a camel or a cow that has a multicompartment stomach. Some water is still lost from the blood, but to deal with this, camels’ hemoglobin—the oxygen-carrying molecule in the blood— has a protein structure that is highly hydrophilic, or water-loving. As a result, camels’ hemoglobin better holds on to water and keeps it within the red blood cells. Camels’ red blood cells are also unusually resistant to bursting when placed in a dilute solution and, therefore, can tolerate a rapid reuptake of water into the blood. The ability of camels’ red blood cells to swell significantly without membrane rupture may be due to a combination of their shape and membrane composition. Camels’ red blood cell membranes have a significantly higher protein composition compared to the red blood cell membranes of less-dehydration-resistant species, and this protein is thought to strengthen the membrane.
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Members of the camel family, which include llamas and alpacas, are also the only mammals that have oval rather than circular red blood cells. The oval shape could alter the distribution of stresses on the membrane and confer rupture resistance. The oval shape also facilitates blood flow in the dehydrated state, as the streamlined red blood cells orient with the long axis in the direction of blood flow, reducing drag as they course through the blood vessels.
Phobic pachyderm? I’ve heard that elephants are afraid of mice. If so, for what reason? Elephants are not afraid of mice, say elephant keepers at zoos and circuses. Stables provide mice with shelter, nesting material, and food, so captive elephants must grow accustomed to encountering mice. There is no reason to think wild elephants have musophobia, fear of mice. An elephant is unlikely to even take notice of a mouse. The jokes and cartoons depicting elephants cowering at the sight of a mouse have ancient roots. Nearly 2,000 years ago, Pliny the Elder, ancient author and natural philosopher, wrote in his Encyclopedia of Natural History, “They [elephants] hate the mouse worst of living creatures, and if they see one merely touch the fodder placed in their stall they refuse it with disgust.” It is not clear where Pliny got this information, but Natural History contains many fanciful things. For example, it is also responsible for propagating the myth that porcupines shoot their quills. Although his work is considered a major achievement in documenting knowledge about the natural world, Pliny relied a great deal on hearsay.
Just hangin’ around Why do some birds gather in certain spots? I can see that the pigeons congregating in public places have found them to be a good source of dropped food. The birds that are more interesting are the ones that sit, sometimes in rows, on the wires that cross the freeway or on signs.
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In areas with few trees, wires and signs are the highest available perches. Being high protects birds from predators and helps them spot sources of food. Lifting off from a high perch is also easier than lifting off at ground level. Some of the birds may be perched near nests they built on the underside of highway overpasses. The wires and signs also serve as “staging” sites, where birds congregate between feeding areas and the places they roost for the night. Various possibilities explain why there are gaggles of geese, bevies of quail, bands of jays, colonies of penguins, coveys of pheasants, broods of chickens, charms of finches—that is, why birds of a feather flock together. In some species, extended families help raise young. Flocking may also protect birds from predators. In support of this possibility, one study found that birds on islands with few predators flocked less than birds of the same species living near abundant predators. Other studies have suggested that flocking together helps birds locate sources of food. Incidentally, birds’ affinity for power lines is a concern for utility companies, which can be held legally responsible for electrocuting them. Also, when large birds empty their bowels as they take off, these “streams” can bridge the gap between the transmission structure and the conductor, causing outages.
Classy choreography I’m curious about how flocks of birds and schools of fish can all change direction at once. More than half of fish species form schools and half of bird species form flocks. Groups range greatly in size, from a few individuals to a 15-mile-long school of herring that Department of Fish and Game biologists measured in San Francisco Bay. Group formation provides protection against predators, facilitates foraging for food, and simplifies the search for a mate—rather like humans hanging out a nightclub.
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Flocking and schooling are emergent properties, the collective outcomes of individual behaviors and interactions among members. No single leader controls group coordination; any member of the group can initiate maneuvers, which may travel along any axis, including from back to front. Because maneuvers occur more abruptly than they could if individuals were simply reacting to their immediate neighbors, some researchers have postulated that animals coordinate group behaviors using “thought transference” or electric and magnetic fields. However, video analysis and computer simulations show that it is not necessary to infer unusual forms of communication to explain flocking and schooling. Group coordination can be replicated by computer models in which individual “animals” follow three simple rules: stick close to neighbors, move away if neighbors are too close, and face the same direction as those nearby. In nature, group members appear to follow the lead of initiators banking toward but not away from the group. Individuals that move away from the group are especially vulnerable to being picked off by predators. To explain the swiftness of maneuver coordination, biologist Wayne Potts proposed the “chorus-line hypothesis” in the journal Nature in 1984. Potts conducted field observations and analyzed slow-motion frames of film taken of flocks of shore birds. He found that one individual or a few individuals initiated each maneuver, which then radiated from the initiation site to propagate through the flock in a wave. The propagation of the wave began slowly but reached speeds two to three times as fast as would be possible, based on visual response times, if the birds were simply reacting to their nearest neighbors. Potts concluded that flocking birds were coordinating their behaviors just as humans do in a chorus line. In a chorus line, maneuvers propagate from person to person almost two times as fast as the maximum human visual response time. This is possible because individuals watch the approaching maneuver wave and time their movements to coincide with its arrival.
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It’s all a blur The human brain registers visual input at about 16 frames per second. I assume that some animals register visual input at other speeds. What variety is there? How did evolution shape this adaptation? What benefits are conveyed by the min/max?
In the early days of movies, it was determined that film had to be advanced at a minimum of 16 frames per second to prevent motion from appearing jerky. The human eye is actually better at resolving rapid movements than that number implies. Film projectors also had a shutter that opened and closed up to three times as the film advanced from one frame to the next. The human eye’s flicker fusion frequency (FFF)—the frequency above which individual movements can no longer be resolved—is about 60 Hertz (Hz), or 60 oscillations per second. Birds have a considerably higher FFF. They can distinguish movements greater than 100Hz. For instance, a fluorescent light oscillating on and off 60 times per second appears continuous to us but looks like a strobe at a disco to a bird. Newer fluorescent lamps with electronic ballasts—the voltage converter at the base of the lamp—flicker at a very high frequency. However, conventional fluorescent lights flicker at twice the frequency of the electrical supply (60 cycles per second in North America and 50 cycles per second in Europe), resulting in flicker at 120Hz and 100Hz, respectively. In aging bulbs, the brightness of the alternate half-cycles may be of unequal intensity, producing flicker at the frequency of the electrical supply itself. Disco Duck lighting can interfere with birds’ search for that special someone. A study of captive European starlings found that, under unflickering lights, female starlings consistently preferred males with longer iridescent throat feathers. Under fluorescent lights with a 100Hz flicker, females’ mate choices were erratic. The researchers concluded that flicker may interfere with visual perception or cause low-level stress that makes the birds less choosy.
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Raptors that pursue other birds may have the highest FFF because they must fly very rapidly while avoiding obstacles and detecting the movements of their prey. Such agility would not be possible if everything blurred together. Some forms of camouflage, such as the stripes on a zebra or bands on a snake, may rely on a flicker fusion effect of a predator’s vision. If a pattern moves across an animal’s visual field faster than the FFF, the markings may blur to match the background. Alternatively, bands moving at a particular speed could dazzle, distracting attention from a body’s outline and making it difficult to determine its speed and direction. Individual nerve cells in the brain regions that detect and analyze motion are tuned to motion in specific directions and at specific speeds. Reptiles have fewer nerve cells that respond to motion, compared to birds and humans. Some of the lowest known FFFs are found in lizards in shady, sheltered habitats in which high-speed chases would be a less effective predatory strategy. Natural selection shaped each organism’s FFF, but it did not prepare humans for the speeds at which we are now capable of traveling. Exposure to a constant speed leads to a reduction in the perceived speed; hence, highway driving gives us a “lead foot.” A reduction in contrast also reduces the perceived speed and makes it seem as if we are going slower when traveling through fog. So if you get pulled over for speeding, you might try telling the officer about your quirky FFF.
Air traffic control We have a hummingbird feeder hanging from a tree limb. These little critters fly through the tree limbs at a high rate of speed without hitting them. I understand that bats have some kind of bat sonar they use to avoid colliding with anything. But what do hummers use to keep from running into things? Hummingbirds have a unique set of anatomical and physiological adaptations that enable particularly complex and rapid flight maneuvers, including the capacity to hover in place better than any other bird.
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In general, birds’ deft avoidance of obstacles during flight is facilitated by their eyes’ high flicker fusion frequency (FFF), the frequency below which individual movements can be resolved. With a high FFF, objects in the surroundings remain distinct instead of blurring together during flight. Hovering to lap nectar from flowers or a feeder requires another visual adaptation to stabilize flight. Stabilization relies on the optokinetic response, a visual reflex to motion across the retina in which head, eye, or body movements are made in the direction of motion. It links eye and environment to establish a stable base for the execution of behaviors. The optokinetic response is not unique to hummingbirds—or even birds in general. However, in hummingbirds, a brain region critical for controlling this response (with a name larger than a hummingbird), the pretectal nucleus Lentiformis mesencephali (LM), is considerably larger relative to total brain size than in other birds. The enlarged LM may also facilitate hummingbirds’ unusual ability to fly backward, because some of the nerve cells in the hummingbird LM respond exclusively to reverse motion. In addition to neural adaptations, hummingbirds have a very high metabolic rate, a large heart, and modified wing bones and musculature. As a result, hummingbirds can beat their wings faster than other birds and produce force on both the up and down strokes. Although hummingbirds do not use echolocation (animal sonar) like bats, some birds—including the Oilbird and the Swiftlets—do echolocate. They use echolocation primarily for entering and exiting dimly lit caves where they have their roosting sites. When hunting outside the caves, they rely on vision. In contrast, insectivorous bats use echolocation to home in on their tiny prey. Echolocating birds can avoid obstacles greater than only about a quarter-inch in diameter, but bats can avoid wires finer than a human hair. In other words, that old rumor about bats getting trapped in your ’do should go the way of the mullet.
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Mama marsupial How do marsupials, such as kangaroos, which keep their young in their pouches for months, dispose of the waste from the young? The sight of a kangaroo joey almost its mother’s size climbing back into mom’s pouch makes it clear that humans are not the only species with grown kids reluctant to abandon the comforts of home. If they could talk, kangaroo moms would probably complain about having to clean up after their mama’s joeys. Kangaroos clean their pouches by sitting back, holding the pouch open with the front paws, and inserting the muzzle into the pouch. Pregnant females begin licking their pouches in earnest before they give birth. They also clean the fur on their stomachs where the tiny newborn will climb to reach the pouch. As females approach their first breeding season, the pouch grows rapidly and sweat glands within the pouch produce a pigmented, oily substance. The pouch secretions may facilitate the cleaning of the pouch. The secretions and the attention to pouch hygiene protect young marsupials by reducing bacteria in the pouch.
Escargot explorer How is it possible for a large snail to place itself on the door of my car? There’s nothing close to the car. For the snail to get there, I think he’d have to come up the side of the tire and under the frame and axel. It appears impossible. Also, why do I find snails on the side of the house, on metal fence posts, and similar places? The suction created by slime allows snails to crawl upside down, so it could have come from the ground. Alternatively, it might have crawled aboard when your car was parked near bushes. According to a BBC report, some determined snails once got into the habit of crawling up and into mailboxes en masse. Apparently, the snails had taken a liking to the taste of envelopes, possibly for the cellulose they contain.
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Snails are most active in damp weather (and rain from sprinkler systems) and at night. In too-dry conditions, snails retreat into their shells and batten down the hatches. They seal their shell aperture with mucus, which dries to form a sheet called an epiphragm. With the epiphragm to prevent desiccation, snails can remain dormant for months. Incidentally, the adhesive mucus snails use to form the epiphragm and attach themselves to a surface contains special proteins that link via electrical charges with other molecules in the mucus. Ongoing research into snail mucus may guide biomimetic (mimicking biology) approaches to the design of glues that work in wet environments.
All in the family Near the Pacific Ocean at Jaco Beach, Costa Rica, I noticed two types of marine snails in the surf zone. What caught my eye was the speed with which they moved. One snail used a rippling motion of the foot to move across the water film. The other actually flapped its foot, similar to a human swimming the butterfly stroke. Do you know of a mollusk expert who might be able to identify these animals? Living organisms are classified into a series of hierarchical groups, from broadest to narrowest: domain, kingdom, phylum, class, order, family, genus, species. Based on your description, Larry Lovell, the collections manager at the Scripps Institution of Oceanography Benthic Invertebrate Collection, and some members of the San Diego Shell Club were able to identify the snail family with reasonable confidence: Olividae. Lovell and colleagues thought that the genus might be Olivella, Oliva, or Agaronia. It was not possible to narrow the species from this description. The family Olividae—dubbed Olives by snail enthusiasts—consists of about 400 species. Olives have glossy, olive-shaped shells with a wide variety of markings. They eat dead animal matter as well as live
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mollusks (other species of snails) and crustaceans (such as shrimp). They seize their prey with the front part of their foot and bring forward the posterior portion of the foot to form a pocket in which they can drag around their prey to snack on. In addition to predation, the snails’ Olympic swimming abilities may help them scramble to a safe place to park on the beach where the next wave will not fling them too high, according to Don Cadien, a marine biologist with the Sanitation Districts of Los Angeles County, who has studied snails for over 30 years. The snails must respond to a habitat that changes constantly, as the height of the surf and the angle of the waves vary with the tides.
Shut-eye for Moby If whales can go only so long without oxygen, do they sleep?
Whales and dolphins are sometimes seen “logging,” resting at the surface of the water like a floating log. During rest, electroencephalograms (EEGs)—recordings of electrical activity in the brain—detect slow electrical waves on one side of the brain, similar to those detected in humans during deep sleep, whereas the electrical activity in the other side of the brain is similar to that in an awake animal. Therefore, whales and dolphins seem to let one hemisphere of the brain sleep at a time. No published reports have documented rapid eye movement (REM) sleep in whales or dolphins. Because in humans REM sleep is associated with dreaming, this suggests that whales and dolphins do not dream. They are the only studied mammals that do not have REM sleep. Another difference is that newborn whales and dolphins do not sleep. Whale and dolphin mothers also go without sleep for substantial periods after the birth of the calf. (Well, maybe they aren’t so different from humans after all.) Over a few months, the calf’s sleep behavior increases to adult levels. When in the water, fur seals, which may spend weeks without going ashore, have sleep behaviors and brain waves similar to those of
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dolphins and whales. Surprisingly, fur seals’ sleep changes as soon as they move onto land. Not only do both sides of their brains begin sleeping at the same time, but they also begin to have REM sleep.
Fish tales What is the largest species of freshwater fish? How big are they? Scientists are not absolutely certain, because there are many poorly studied fish in very large, deep, or remote bodies of water. Claims about large fish also are prone to error or exaggeration. (You know, the big one that got away!) Sturgeon are likely the largest fish found in fresh water, although they spend most of their lives in marine environments. Some species of sturgeon that spawn in the rivers of Russia and Europe have reportedly reached 12 to 15 feet and weigh up to 2,000 pounds. Overfishing has made the largest specimens scarce. For the title of the largest fish species that spends its entire life cycle in fresh water, contenders include the arapaima and goliath catfishes of the Amazon, the Chinese paddlefish, the Mekong giant stingray, and the Mekong giant catfish. Most of these species have become so rare that their maximum size is difficult to determine. The Guinness Book of World Records lists the Mekong giant catfish as the largest freshwater fish. In 2005, fishermen in northern Thailand caught a 646-pound Mekong giant catfish, the most massive since Thai officials started keeping records in 1981.
Fish-icles How can fish live out the winter in 30°F water yet a human can last only five minutes? It must have to do with a special oil of some kind inside the fish. But what’s so special about it and how does it do the trick?
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In marine mammals, such as seals and whales, fat does play a role—an insulating layer of blubber keeps body heat from escaping. Like us, they are warm-blooded and need to maintain their body temperature within the narrow range in which their enzymes, cells, and organs function best. Humans also have adaptations that allow us to keep cool when the weather is hot and keep warm when the weather is cold. For example, we shiver and reduce blood flow to the skin so we lose less heat to the environment. However, our ability to thermoregulate has limitations. As a result, it is not uncommon for people swimming in cold water to perish even if they are close to shore. Immediately upon entering cold water, uncontrollable hyperventilation makes swimming difficult. As the muscles cool, muscle control becomes impaired. Heart attack risk increases as the core body temperature drops and, as nerve cells in the brain lose the ability to communicate, consciousness is lost. Fish, which are cold-blooded, move to the bottom of ponds or lakes when the water gets too cold, and their metabolism slows dramatically. The metabolism of hibernating mammals also slows dramatically, although, unlike fish, most maintain their body temperatures close to normal. Some mammals, such as the hibernating ground squirrel, allow their body temperatures to fall to just above freezing, a feat scientists still are not certain how they manage to accomplish. In fresh water, cold-water fish will not freeze to death as long as the lake or pond is of sufficient depth that it does not freeze solid. The situation is different in salt water. The presence of salt in water allows it to get colder than fresh water before it freezes. To survive in water that would make their cousins from tropical and temperate regions into frozen fish sticks, Arctic and Antarctic fish have developed antifreeze molecules. The antifreeze molecules are proteins that bind to tiny ice crystals in the blood of the fish and prevent the ice crystals from getting bigger. Exactly how the proteins do this is under investigation. It’s not just a matter of academic interest. These proteins are hundreds of times more effective than chemical antifreezes at the same concentration.
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They have potential applications as nonpolluting deicing agents for airplanes, or in preventing ice crystals from damaging tissues and organs that are being cryopreserved.
Condor kissing cousins We know of the heroic efforts being made by zoologists and conservationists in rebuilding populations of certain animal species that are on the verge of becoming extinct. These populations are often rebuilt from very small numbers of individuals. What risks do these populations face as a result of this lack of genetic diversity? The rebuilding of the California condor population is a case in point. What effect is the lack of genetic diversity likely to have? Can genetic diversity ever evolve in such a case?
Genetic diversity enables populations to respond to the pressures posed by environmental changes. A variety of studies have shown that a reduction in genetic diversity has negative consequences for health and reproductive fitness of a population. In rebuilding populations, the lack of genetic diversity in small populations can be compounded when a limited subset of individuals produce a large majority of the offspring. For example, a genetic analysis of repatriated, captive-bred giant Galapagos tortoises showed that a small subset of breeders dominated the gene pool. Unfortunately, fecundity in captivity does not necessarily correspond with success in the wild. For instance, traits that help animals better withstand disease epidemics are not necessarily selected for in captivity. Just 23 individuals were left in 1982 when the remaining California condors were placed in a captive breeding program. The population has since increased to nearly 400, just over half in captivity and the rest in the wild in California, Arizona, and Mexico. Genetic diversity in condors is low, so the captive breeding program aims to preserve the remaining genetic diversity. According to Oliver Ryder, associate director of genetics at San Diego’s Center for
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Conservation and Research for Endangered Species, genetic profiling was used to select and pair minimally related individuals from the original breeding population. One genetic disease that has been identified in condors is chondrodystrophy, which disturbs bone growth and kills affected chicks. Ryder states that the disease may be the result of reductions in population size that predate the captive breeding program. New genetic diversity can arise by mutation over long periods of time. However, the biggest immediate threat to the condors is not lack of genetic diversity. Condors, which are scavengers, eat carrion left by hunters. As a result, condors ingest lead fragments from bullets and frequently suffer lead poisoning. Efforts such as new restrictions on the use of lead-containing ammunition seek to reduce this threat.
Long-term companions Domestic adult dogs come in all sizes. Domestic cats come in onesize-fits-all. Why? Is it linked to genetic limitations? Artificial selection through human intervention has played a much greater role in the evolution of our canine friends than of our feline friends. For most of the history of cat domestication, natural selection has run its course. Dogs originated from gray wolves at least 15,000 years ago. The process likely began when a group of less-fearful wolves was attracted to encampments of hunter-gatherers to scavenge kills. The humans may have tolerated the wolves’ presence because they warned of invaders during the night. Eventually, humans took wolf pups as pets and established control over their mating. Not much is known about this initial phase of dog domestication, but 10,000 years ago, dogs already ranged from a size similar to a small terrier to that of a Great Dane. Cats adopted humans at the dawn of agriculture about 10,000 years ago, in what is known as the Fertile Crescent in the Middle East. Genetic studies reveal that all domestic cats are descended from Felis silvestris lybica, a wildcat native to this region.
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Grain stores and trash heaps near early human settlements were plentiful sources of rats and mice, which wildcats tolerant enough to live near humans could have exploited. As these cats proliferated, natural selection would have favored tamer individuals. Archeological evidence suggests that cats may have been taken as pets soon after they moved into human settlements, but the first unmistakable evidence of full domestication is no more than 3,600 years old. Egyptian paintings from that time depict cats in households, wearing collars and eating from bowls. By 2,000 years ago, cats had spread to Greece, Rome, and the Far East along trade routes, likely taken aboard ships to control vermin. Humans probably did not directly control cat breeding at this time, but as felines fanned out around the globe, new breeds emerged. This occurred through genetic drift when populations of domestic cats were isolated from each other and led to 16 “natural breeds.” The remaining breeds developed over the past 150 years by artificial selection. The desire for more extreme pets, coupled with in vitro fertilization, has recently increased the pace of cat breeding. Dwarf cats, short-legged cats, domestic cats crossed with wild cats, curly-haired cats, and bald cats are already available. Designer companions can have drawbacks, however: Selective breeding from a small foundation stock often leads to genetic disorders.
Tears of a hound What is the substance that accumulates in the corners of some dogs’ eyes? The substance that accumulates around dogs’ eyes (and our eyes) mainly consists of evaporated tears. Tears are not simply salt water; they consist of three layers and many different compounds. Closest to the eye is a mucus layer consisting of proteins made by the conjunctiva, a thin membrane covering the eye. The proteins surround grit as well as bacteria and viruses, to protect the surface of the eye.
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The middle layer is what we normally think of as “tears,” salt water secreted by the lachrymal glands, which are in the upper outer corner of each eye. This middle layer also consists of proteins and a variety of other compounds, including oxygen and nutrients to supply the cornea. Finally, the eyelid’s meibomian glands produce the outer layer of tears, an oil that helps reduce the evaporation of the watery middle layer. At night, when the eyes move behind the closed eyelids, fluids are pushed toward the corners of the eyes. The water evaporates leaving behind the proteins, salts, oils as well as dead cells and any dust or debris that had found its way into the eye. While this accumulation is normal, the recurring presence of thick yellow or greenish mucus is a sign of bacterial or viral infection. Tears normally flow across the eye and drain into two tiny canals that open near the inner end of each eyelid. You can see the openings (puncta) to these canals—the nasolachrymal ducts—if you gently tilt your lower eyelids forward. These canals eventually open into the nose. You taste eye drops because they flow down these canals into the nose and onto the tongue. When tear production exceeds drainage (for example, when we cry), tears leak from the eyes. In some breeds of dogs, the nasolachrymal ducts are easily blocked. Some breeds also have very shallow eye sockets, so their tears constantly run down their faces. Although the tears look clear, they contain small quantities of iron, which is left behind in the dog’s fur as the water evaporates, causing a rust-colored stain as the iron accumulates over time.
Sorry, Snoopy Rosie O’Donnell said it recently on TV, and now I’ve heard it on the news: Allowing a dog to lick a wound is good for healing, dogs have magic saliva for healing, and a dog’s mouth is cleaner than a human’s. However, I read once that this is an old wives’ tale. I would hate for someone to follow this advice only to get an infection. Please clear this up once and for all.
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As with a lot of bad medical advice, this is based on a grain of truth but ignores contradictory evidence. The grain of truth is that dogs’ saliva plays an important role in protecting puppies from disease. The contradictory evidence is that Lucy was right: Dogs’ mouths are teeming with bacteria. For newborn puppies, mom’s good personal hygiene can be lifesaving. Pregnant dogs frequently lick their mammary and genital areas, the first places puppies will contact. Before a puppy gains protective immunity from mother’s milk, exposure to fecal matter on mom’s fur can be deadly. Studies have shown that dogs’ saliva kills at least two types of dangerous bacteria found in feces. Saliva is a complex substance. Canine saliva, like human saliva, contains a number of antibacterial compounds. Nevertheless, it is not effective against all bacteria. Most notably, it does not kill Staphylococcus aureus or Pseudomonas aeruginosa, two common wound contaminants that can cause deadly skin infections. Since man’s best friend has a habit of scavenging from rather unsavory sources, it isn’t surprising that one study found 84 different kinds of bacteria within those slobbery jaws. Some of the bacterial species were also found in human maws, but others were new to science. Not all bacteria are harmful, and licking a wound might have other benefits. For example, it could remove foreign material embedded in the skin and stimulate blood flow to nourish the region. Saliva also contains growth factors, chemicals that stimulate cells to proliferate. Therefore, in the best-case scenario, licking could accelerate healing, which may explain why people in the Middle Ages sometimes purportedly encouraged dogs to lick their wounds. An example of the worst-case scenario is documented in the case of a woman whose poodle licked a wound on her toe. The woman developed a persistent bacterial infection in her artificial knee, which had to be surgically removed and replaced as a result. The bacterial species involved, Pasteurella multocida, is also often implicated in infections related to dog bites.
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Strange bedfellows Why are animals that are hybrids between two different species, such as mules, sterile? Efforts to understand the mechanisms of hybrid sterility date at least as far back as Aristotle, who pondered the sterility of mules. The question was of great interest to Darwin, too, because it is relevant to understanding how new species arise. Today researchers recognize that no single mechanism explains sterility in all hybrid animals. What’s more, not all hybrids are sterile. Mules are the offspring of a female horse and a male donkey. A cross between a female donkey and a male horse is called a hinny. Horses have 64 chromosomes and donkeys have 62; mules and hinnies have 63 chromosomes. An odd number of chromosomes is problematic because chromosomes usually come in pairs, which are separated in a process called meiosis to make egg and sperm cells with half the original number of chromosomes. Meiosis can sometimes occur normally with an odd number of chromosomes, as evidenced by documented cases of fertile mules and hinnies. In one published account that included DNA parentage testing, a healthy offspring of a hinny and a donkey was found to have 62 chromosomes. Sterility can also arise in crosses between different subspecies (such as two subspecies of mice) when both parents have the same number of chromosomes. The genetic changes that lead to hybrid sterility in these crosses are still being unraveled, but a variety of genes have been implicated. Specifically, because genes interact with other genes, flawed interactions between the genes of the father species and those of the mother species can prevent an offspring from developing normally. The genes from the different species may not be able to function in complexes together, or the timing of when genes switch on and off may be mismatched. Hybrids may also fail to have offspring because they do not inherit the courtship patterns of either parent species. Differences in
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breeding seasons, behavioral rituals, and scents that help animals find a potential mate mean that hybrids between species are relatively rare in the wild, although they do happen. For example, in 2006, a hunter shot a bear that later genetic testing revealed to be a cross between a grizzly and a polar bear. In captivity, different species have more opportunity to become familiar with each other. In zoos, for instance, tigons (the cross of a male tiger with a lioness), ligers (from a male lion and a female tiger), and leopard/lion crosses are well known, and some of the big cat hybrids are fertile.
Same or different? Careful scanning of endangered species lists demonstrates a dichotomy within scientists: lumpers versus splitters. Such lists may include groups of animals that lumpers would consider the same species as a non-endangered population: races, subspecies, forms, variants, and more. Simple request: Define species. In 1942, Ernst Mayr, one of the giants of modern biology, defined species as “groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.” Most biology students learn Mayr’s definition, but it has limitations. The definition fails for species that do not reproduce sexually. Also, it may not be feasible to determine whether geographically separated populations can interbreed. Furthermore, hybridization between plants or animals considered separate species occasionally occurs in nature. An obvious alternative is to define species according to physical or behavioral characteristics. This approach has a long history, but it, too, has caveats. Most notably, the females and males of particular species (for example, certain birds and butterflies) appear so different that they can be initially identified as separate species. Countless papers have been written about how to define and identify species. One recent review turned up more than two dozen distinct definitions. Of course, this academic debate has real-world
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implications. For example, according to conventional classifications (by the lumpers), there are around 10,000 species of birds worldwide, but some biologists (the splitters) believe that 20,000 is a more accurate evaluation. The U.S. Endangered Species Act (ESA) of 1973 defines species to include “any subspecies of fish or wildlife or plants, and any distinct population segment of any species or vertebrate fish or wildlife which interbreeds when mature.” One important feature of this definition is that it permits specific populations of animals or plants to be listed as threatened or endangered in addition to entire species. For instance, in the lower 48 U.S. states, grizzly bears are listed as threatened, but in Alaska, the relatively healthy grizzly bear population is not given ESA protection. In other words, conservation efforts consider more than the nebulous term species. Still, the decision to list a population is by no means clear cut. Populations to be protected are considered on a case-by-case basis according to many factors: the local ecology, the population’s history, physical characteristics, behavior, and genetics. Preserving genetic diversity within species is an essential component of conservation efforts. Modern genetic techniques make it possible to compare the variability within and between populations. The U.S. Fish and Wildlife Service may turn down petitions for the ESA listing if it does not determine the populations to be distinct.
Ancient alphabet Do all known organisms inhabiting or having inhabited our planet, in the air, on the surface, below the surface, or in the sea have some common DNA?
Genes that are common across all species are rare. About 60 genes, 0.2 percent of human genes, are found in all the genomes that have been sequenced, and this number may decline as more species’ genomes are deciphered. The reason for the limited genetic overlap among large numbers of organisms is that, over time, different organisms have evolved new
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molecular strategies to accomplish fundamental tasks. In contrast, the overlap between any two organisms is much larger. For example, 61 percent of the genes in fruit flies are also found in humans. Genetic overlap between species has practical implications for researchers. Most advances in understanding human development and disease come from research on flies and other organisms that are easy to breed, raise, and manipulate genetically. The chemical language in which genetic blueprints are written has also changed over time, although considerably less than the genes themselves. All present-day cellular organisms, including bacteria, have DNA genomes, but some viruses have RNA genomes. The consensus among evolutionists is that an RNA world preceded our DNA world. Both DNA and RNA have alphabets consisting of four chemical letters, strings of which spell out the instructions to build all the components of an organism. The letters are attached to a backbone composed of sugar molecules. During the synthesis of protein, sequences of chemical letters are translated into sequences of amino acids, the building blocks of protein. Only two chemical differences distinguish DNA and RNA, but they make DNA a more reliable genetic blueprint. One difference is that RNA’s (ribonucleic acid’s) component sugar, ribose, is replaced by the more stable deoxyribose in DNA (deoxyribonucleic acid). The other difference concerns the chemical letters, or bases, that spell out the genetic code. Specifically, U, one of the four bases in RNA (A, C, G, U), is replaced by another base, T, in DNA. An exception is the few viruses that have a kind of intermediate RNA–DNA genome with deoxyribose and the base U. Just as sloppy cursive can convert one letter into another, “sloppy” chemistry can convert a C into a U, but not into a T. Therefore, in DNA but not in RNA, a cell’s proofreading apparatus recognizes a U as a messed-up C, because DNA should not contain any Us, and fixes it before the mutation can be passed on to daughter cells. Researchers compare known genomes to debate the nature of the last universal common ancestor. But even if the identity of the last universal common ancestor—the single-celled organism thought to be at the root of the tree of life—was known for certain, it would not be possible to say whether all past organisms shared genetic material.
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If organisms with a different type of genetic material existed but died out without passing it on, their existence—and the existence of the different kind of genetic material they contained—might never be discovered.
Bad behavior Has the behavior of any species knowingly or unknowingly caused the species’ own extinction? Although behavioral characteristics are not known to have extinguished any species in the absence of an external destructive force, behavior is often a key factor in extinction risk. Behavioral constraints may make it impossible for a species to adapt to new threats, or the threats may alter behavioral patterns and hasten extinction. One behavioral constraint is the inability to respond to novel predators. Brown tree snakes introduced to the island of Guam shortly after World War II caused the loss of more than a dozen bird species. Susceptibility to introduced predators, in addition to human exploitation, also played a role in the extinction of the Dodo in the 1600s. Behaviors that limit dispersal, such as sedentary habits, the unwillingness to cross certain terrains, or the inability to move between fragmented forests due to intolerance to sunlight, leave a species especially vulnerable to habitat loss. Raptors that nest atop electricity towers, and birds, fish, and sea turtles that are attracted to artificial lights also exhibit behaviors that increase extinction risk. For species that aggregate in large social groups, a behavioral phenomenon known as the Allee effect, a relationship between population density and per-capita population growth, can be the final nail in the coffin when external factors reduce the population. Instead of rebounding when the external threats are removed, a population may continue to decline because behaviors that depend (in some species) on numbers, such as mating, foraging, and defense against predators, may be disrupted. The Allee effect may have led to the ultimate demise of the Passenger Pigeon, thought to have once been the most common land Download at www.wowebook.com
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bird. Hunting and habitat destruction decimated the once enormous flock sizes of the birds. Flock size reduction interfered with the birds’ ability to nest in colonies, which led to decreased per-capita reproduction and increased vulnerability to predators. In the early twentieth century, when it became clear that the Passenger Pigeon had gone extinct, some blamed the birds’ behavior for their own extinction. Today insights into behavioral quirks such as the Allee effect are used to help threatened species. To attract young Griffon Vultures to new nesting sites, cliff faces have been splashed with white paint to imitate bird droppings. Decoys and audio recordings of birdcalls are used to attract colonial nesting birds to new nest sites. Flamingos overcome the lack of social stimulation that prevents small groups from breeding in captivity with help from a bachelor pad–inspired modification. Mirrors placed around captive flamingo flocks stimulate them to engage in courtship displays.
Leaping lemmings Are stories about lemmings engaging in mass suicide based on scientific fact?
As with much folklore, the belief that lemming populations increase over a four-year cycle until the lemmings run out of food, when they jump off the nearest cliff or drown themselves in the ocean, is a little science and a lot misconception. On one hand, long-term studies of lemmings and other rodents show that dramatic oscillations in population densities do occur. Nearly all species of Arctic rodents have population cycles. On the other hand, the rhythm of the population cycles varies among species. Also, the same species in different regions go through different population cycles. Fluctuations may be seasonal, multiannual, or both. The timing of the cycle tends to be consistent at a particular site, but the size of the population boom and bust varies from cycle to cycle.
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The lemming suicide myth has its origins in Scandinavia, in the highlands between Norway and Sweden. As the lemming population there grows, lemmings migrate downhill and a fiord channels their movements toward the sea. Some head out on ice flows, likely because they are searching for a new habitat, not because they are intent on self-destruction. Directed movements toward the sea have not been observed of lemmings living where the tundra is low and flat in the North American Arctic. The myth of lemmings deliberately plunging to their death was perpetuated by a 1958 Disney documentary, White Wilderness. This apparent example of mass lemming suicide was faked by the film crew, who hurled the hapless creatures off a cliff, a deception described by several sources, including the book Do Lemmings Commit Suicide?: Beautiful Hypotheses and Ugly Facts, by Dennis Chitty (Oxford University Press, 1996). Over the past century, in scientific journals and at conferences, ecologists have fiercely debated the causes of rodent population cycles. Explanations include diseases, parasites, weather, predators, food shortages, and social factors, such as territorial interactions that make populations self-limiting. All these influence rodent populations, but no one factor seems to explain observed cycles in all regions and among all species. For example, one study concluded that weather conditions, specifically hardness of the snowpack and how amenable it is to rodents burrowing beneath, out of sight of predators, could explain lemming cycles. Another study concluded that food shortages were the key factor in population cycles of lemmings, which primarily eat slow-growing mosses. In population cycles of voles, another type of rodent, the study concluded that predation was the likely cause, based on the speed of the population crashes. So the unanswered questions are keeping the science as colorful as the lemming lore itself.
Sink like a stone Why do some individuals sink in water yet others float?
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Floaters are more buoyant than sinkers because of their relative amounts of air (in the lungs and intestines) and fat, which are less dense than water, compared to bone and muscle, which are denser than water. A low-tech method to determine body composition involves weighing an individual who is fully submerged in water. On average, women and children are more buoyant than adult males, and adults become more buoyant as they lose bone and muscle mass with age. Buoyancy can be increased slightly through breathing exercises that expand lung capacity. Changes in lung volume play a greater role in buoyancy control in king penguins and sea lions. These animals compensate for seasonal changes in body fat by adjusting the amount of air in their lungs during dives. Aquatic animals have a range of buoyancy-control strategies, because if an animal is the same density as the freshwater or saltwater environment in which it lives, hovering motionless is easier and hunting and swimming require less energy. Similar to penguins and sea lions, many fish exploit the fact that, at low to moderate depth, the density of a gas is negligible compared to that of water. These fish have a sort of on-board inner tube, a gasfilled cavity called a swimbladder. The thick layer of subcutaneous (under the skin) fat that diving mammals rely on to limit heat loss in cold water functions as a flotation device. Fish also use fat to achieve neutral buoyancy. Depending on the species of fish, fat may be stored in the liver, in muscles, in the intestines, or subcutaneously. Fat may also be stored in the swimbladder, in special oil sacs, or within the bones. Storing fat within the bones, which are typically the densest part of the body, can sometimes reduce the skeleton’s density below that of sea water. Other strategies for decreasing the density of the skeleton include reducing the size of the bones or reducing the bones’ mineral content. In some cases, nearly the whole skeleton may consist of cartilage instead of bone. During swimming, buoyancy and hydrodynamics both play a role. When humans or other animals swim at the surface, a higher position
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relative to the water has the advantage of reducing drag. When animals with pectoral fins or flippers swim quickly through the water, a lift force is generated. As with airplane wings, this is due to the difference in pressure created as water flows more quickly over the top of the fins than the bottom.
Master of disguise How do some animals change colors so that they match their surroundings? Seasonal color changes in animals, such as the Arctic fox, are triggered by changes in the length of daylight or temperature. Hormone levels, which these environmental influences alter, control the amount of pigment the hair follicles produce. Because hair is dead tissue, coat color changes relatively slowly as new fur grows in. On the other hand, some species of lizards—most notably chameleons—and certain species of fish and octopi can change color within minutes. These rapid color changes are not always for camouflage; they can also be used to communicate, as in rivalry fights, or to indicate readiness to mate. Light is frequently the trigger that initiates color change to match the environment, although temperature and gravity-sensing systems (for example, in cuttlefish) can play a role as well. Light energy can stimulate color-producing cells directly or indirectly via the visual system and subsequent neural and hormonal responses. Color can be produced in two different ways: via pigments or via special reflecting structures. Pigments look the same from different viewing angles. Structural colors are iridescent—they shimmer—and appear to change hue according to the angle from which the surface is viewed. Pigments, which absorb certain colors of light and reflect others, are contained in cells called chromatophores. A circular muscle surrounds each chromatophore. When the muscle contracts, the pigment is pushed to the surface of the cell and more pigment is visible than when the muscle is relaxed.
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Structural colors can be produced by the reflection of light off stacks of thin, transparent crystals. When white light hits the stack of crystals, some of the light reflects off the top crystal, and some reflects off each of the deeper crystals. Since one set of reflected light waves travels slightly farther than the next, the waves get out of phase with each other and interfere. Some colors are completely out of phase and cancel out; colors in other reflected waves reinforce each other and appear brighter. Some fish can change the distance between the crystals, which changes the way the light waves interfere and, consequently, the color of the reflected light. For other animals, matching their surroundings is a case of “you are what you eat.” Nudibranches—sea slugs—match the coral that serves as their habitat and fodder by depositing pigment from their food in their skin. When they move to coral of a different color, the pigment from their new food source gradually replaces the old.
Elementary, my dear Watson We often read about animals able to solve problems or use tools in new ways. How similar are animal and human thinking considered to be? On one hand, many philosophers argue that thinking about thoughts requires language, so logic cannot exist without language. On the other hand, if thinking is defined as the ability to act on information flexibly rather than following what has been genetically preprogrammed, many animal species, including some invertebrates, think. In a recent laboratory study, crows spontaneously applied three tools in sequence to reach a snack, a skill not previously observed in a nonhuman animal. In the avian equivalent of thumbing his nose at the researchers, one of the crows solved the puzzle by leaving the test room to retrieve a long twig from the aviary, instead of playing along and snagging successively longer tools from the clear tubes provided. Crafty crows, octopi that escape their tanks to steal fish from nearby aquariums, Alex the African Grey Parrot who could count and add, and Washoe the chimpanzee who learned rudimentary American
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Sign Language and taught signs to another chimp are just a few of many examples of animals reasoning. On a broad structural level, human brains are similar to those of other mammals, especially other primates. On the microscopic level, humans have more nerve cells and more connections between nerve cells in some brain areas, particularly those associated with language and complex social thought. As with brain differences, the dissimilarities between animal and human thinking are mostly a matter of degree. For example, although some animals teach, their ability to observe, judge, and modify another’s behavior is rudimentary. Animals can deceive other animals in ways that show they have some understanding of another’s mental processes, but they find deception difficult to learn in some situations. Over hundreds of trials, only one of four chimpanzees learned to look at the wrong container to mislead a “bad trainer” who would steal the food if the chimp revealed which container was full. Animals grasp the associations between causes and outcomes, but some causal relationships are resistant to learning. Still, humans also draw false conclusions about cause and sometimes reason poorly in some of the same laboratory puzzles used to test animal reasoning, such as selecting the best method to retrieve a banana with a rope. Humans in these studies give a rationale for choosing a flawed method, so an animal’s failure on a researcher’s test does not definitively prove it is incapable of the necessary reasoning processes.
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3 Vitally vegetal It’s easy being green A video of a Venus flytrap plant capturing an insect convinces me that there is a link between plant and animal life. What does the scientific community think about this relationship? The snapping shut of a Venus flytrap leaf in 100 milliseconds certainly clashes with the view of plants as inanimate. Its rapid movement led Charles Darwin to call the plant “one of the most wonderful in the world.” The usual connection between plants and animals in the food chain is also inverted by hundreds of other species of (generally more passive) carnivorous plants. But carnivorous plants are not the only examples of vegetation capable of rather unplantlike things. Screenwriters searching for the perfect B-movie plant protagonist could take inspiration from the walking palm, found in the rainforests of Central and South America. The tree slowly “walks” from shade to sunlight by growing new roots toward the light and allowing the old roots interfering with its wanderlust to die. Plants detect, integrate, and respond to many environmental signals, including light, water, minerals, gravity, and soil structure. Plants also have a form of “memory.” For example, plants that reorient their leaves during the night to anticipate the direction of sunrise continue to do so for a few days after being placed in cabinets under artificial lights. Furthermore, new evidence suggests that plants can recognize their kin, something many animals cannot do. Plants of at least some 53
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species sprout roots less aggressively if they detect a relative growing nearby and more aggressively if their neighbor is a stranger. These discoveries have led to the recent founding of an international scientific society devoted to the study of plant neurobiology. A handful of scientists have even gone so far as to propose that plants harbor brainlike units in the tips of their roots. Other scientists are vehemently opposed to the use of the term neurobiology in reference to plants. Although they agree that plant cells can communicate via electrical signals, they counter that no evidence points to nervelike structures in plants. Based on gene sequence data, plants and animals diverged an estimated 1.6 billion years ago from their last common ancestor, a single-celled organism. Sometime after that, plants incorporated the bacterial chloroplast, a cellular component that allows plants to photosynthesize. Nearly all life on Earth would perish without plants to convert the sun’s energy into sugars through the process of photosynthesis. In school, we all learned that plants can photosynthesize, but animals cannot. Many animals, such as sponges, coral, jellyfish, and sea anemones, can photosynthesize by cheating—partnering with algae. Of course, nature loves giving us exceptions to our rules, and at least one photosynthesizing animal exists: the green sea slug Elysia chlorotica. Unlike animals that partner with intact algae cells, the green sea slug extracts chloroplasts from algae it consumes and then holds the chloroplasts within its own cells. Especially surprising to researchers was the finding that the chloroplasts continued to function in the sea slugs’ cells, even though animals cannot manufacture the chlorophyll needed to keep chloroplasts in good working order. It turns out that sea slugs also steal enough genetic material from the algae to make the chlorophyll itself. Theft accomplished, a sea slug can satisfy its appetite by sunbathing.
Freeloading flora I read that mistletoe is a parasitic plant. If plants are organisms that produce their own food by photosynthesis, how can a plant be a parasite?
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Not just holiday partygoers must beware of finding themselves under the mistletoe. Fir trees parasitized by mistletoe have stunted growth and deformations that cause substantial losses for the lumber industry. A parasite is defined as an organism that spends part of its life associated with a host individual, in a relationship that is beneficial to the parasite at the expense of the host. About 4,000 species of plants, approximately 1 percent of all flowering plants, are parasites. Some parasitize a wide range of host species, while others utilize one or a few. Often the only distinguishing feature of a parasitic plant is an attachment to a host, but this connection may be hidden underground. The connection is a round, swollen structure called a haustorium that penetrates the host’s stem or root. The haustorium establishes connections with the vessels in the host plant and transfers water and nutrients to the parasite. Parasitic plants vary in terms of their dependence on the host. At one extreme are hemiparasites. They have chlorophyll and can photosynthesize, but they rely on the host for water and minerals. Some hemiparasites are able to complete their life cycles without parasitizing another plant, but they may not survive drought without tapping into a deep-rooted host. At the other extreme are holoparasites, which lack chlorophyll and cannot survive without the sugars produced by a photosynthesizing host. Plants release attractants and repellents that affect soil microbes, insects, and other plants. Parasitic plants find suitable hosts by detecting the chemicals they release. Dodder, a parasitic plant that is on the U.S. Department of Agriculture’s noxious weeds list, can distinguish between the chemicals released by wheat and those released by tomato plants. It can parasitize either, but given the choice between the two, dodder grows preferentially to tomatoes. Dodder seeds contain limited energy reserves and will die if they do not sniff out and attach to a host within a few days of germination. Unlike dodder, some parasitic plants do not germinate unless they detect chemicals from an appropriate host in the vicinity. Chemical cues between parasite and host are also a prerequisite for the formation of the haustorium.
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Although many are agricultural pests, parasitic plants can benefit ecosystems. For example, fruit, flowers, and foliage of mistletoe are attractive food sources for birds. Mistletoe also provides them with shelter and nesting material. Perhaps mistletoe is good for romance after all—avian romance, that is.
Kingdom of their own What exactly is a lichen? Is it considered a plant? How can lichens survive on rocks?
A lichen is a fungus that has partnered with either cyanobacteria (formally known as blue-green algae), green algae, or both. About one-fifth of fungal species form these partnerships. The algae or bacteria provide carbohydrates from photosynthesis, and the fungus provides the photosynthesizing partner with water and mineral nutrients. Lichens are not classified as plants, although they were in early classification schemes, which separated organisms into just two kingdoms, plants and animals. Now three more kingdoms have been added (four more, in some classification schemes), including the kingdom fungi. Lichens are classified as fungi, despite their algae partners (which fall into two different kingdoms of mostly singlecelled organisms), just as coral are considered animals, despite their algae partners. One adaptation that helps lichens survive on the surface of rocks is lichens’ dehydration tolerance. When deprived of water for long periods, they enter a state of suspended animation. Upon rehydration, photosynthesis and respiration rapidly reactivate. The cycle of dehydration and rehydration contributes to rock weathering due to the contraction and expansion of the fine threads of the lichen that penetrate between rock crystals. Lichens also release acids and other substances that facilitate the uptake of minerals. Lichens can very effectively accumulate nutrients, which is an advantage when nutrients are scarce, but it also makes them sensitive to atmospheric pollutants. They are commonly used as biological monitors in pollution studies.
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Seedless seeds How is seedless fruit produced, and how is it possible to have seedless watermelon seeds? Depending on the type of fruit, changes in chromosome number, alterations in specific genes, or externally applied plant growth hormones are responsible for ending seed-spitting contests as a summer pastime. Seedless mutants arise spontaneously in some fruits, such as bananas. Farmers cultivate seedless banana plants they have selected from the wild by sowing shoots that sprout from the parent stalks. The exact genetic mutations that give rise to seedless bananas have not yet been characterized. Seedless watermelons grow on plants that are triploid—that is, that have three copies of each chromosome. The term ploidy refers to the number of complete sets of chromosomes in a cell. Triploid watermelon plants are the progeny of one parent plant with the normal diploid (double) set of chromosomes and one parent that is tetraploid (with four sets of chromosomes). To produce tetraploid plants, chromosome duplication is induced by treating normal seedlings with a chemical that interferes with cell division. The triploid seeds that result from crossing diploid and tetraploid watermelon can sprout and mature, but the triploid watermelon plants are infertile. This is because an odd number of chromosomes cannot be neatly divided in half during the production of egg and sperm cells. To initiate fruit formation, flowers on triploid watermelon plants must be fertilized with pollen from normal diploid plants. So the two types of plants are grown together, and seedless watermelon seed packages contain both types of seeds. When the triploid plants are fertilized with pollen from diploid plants, seed formation begins but then fails, resulting in the pale, soft undeveloped seeds found in seedless watermelons. Fruit and seed development are usually closely linked. Successful pollination brings together sperm and egg, from which the embryo within the seed develops. Pollen also produces a plant hormone known Download at www.wowebook.com
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as gibberellin. It triggers the increase of another hormone, auxin, within the plant’s ovary, simulating the ovary to begin to develop into a fruit. As the embryo develops, it releases a variety of chemical signals. These signals control the rate of cell division in the surrounding fruit, as well as the expansion of cell volume that greatly increases fruit size. In the absence of normal seed development, hormones sprayed on plants can be used to control fruit development. For example, gibberellin is applied to Thompson seedless grapes to improve quality and yield. Genetic engineering is another option to induce fruit development in the absence of seeds. Patented techniques involve switching on chemical signals that seeds ordinarily produce. Perhaps future generations will miss out on a universal bit of childhood folklore, “That seed you swallowed is going to grow in your tummy.”
Fried green tomatoes How does a tomato turn red when ripe? Where does the color come from? Various hormones control plant growth and development. Ethylene is the hormone that controls ripening in tomatoes and other types of fruit (a tomato is considered a fruit because it develops from the ovary of a plant). Ethylene is a gas. It makes green, hard, starchy, sour, unripe fruit fragrant and delicious by stimulating the production of many enzymes, nature’s catalysts, inside fruit cells. The enzymes break down acidic components, making the fruit less tart. They also digest starch into its component sugars. In addition to giving fruit its sweetness, the presence of the sugar molecules causes water to be drawn into the fruit, making it juicier. Moreover, the enzymes break down pectin, the glue that holds fruit cells together, and soften the fruit by allowing cells to slide past each other. The enzymes produce aromatic compounds as well. The green color disappears as enzymes digest chlorophyll. This unmasks other pigments (especially yellow). Some fruits produce new pigments (especially red). The red in most fruits, leaves, and flowers are pigments called anthocyanins.
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Ethylene is the reason “one bad apple spoils the bunch.” Wounds or disease stimulate fruit to release ethylene. Therefore, a bad apple can cause the other apples in a basket to ripen quickly. In modern fruit warehouses, filters are used to absorb the ethylene being produced. Still, in the United States, about 50 percent of produce is lost to spoilage.
Sweet autumn color Anthocyanins produce sugars and give leaves the brilliant reds when the green disappears. Can you make syrup from any deciduous tree, or only those whose leaves turn red in fall (like maples)? Anthocyanins are indeed the pigments responsible for the vibrant reds of autumn. They have long puzzled scientists because anthocyanin production switches on as leaves are beginning to die. It is like having your car painted before taking it to a junkyard. In contrast, orange and yellow pigments are present all summer, albeit masked by green chlorophyll. A reaction in the leaf between sugars and a chemical precursor to anthocyanins forms the red pigment. Sunlight is required for this reaction, so the tops of trees turn red first, and sunny autumn days enhance the production of anthocyanins. In addition, dry weather increases the concentration of sugar in the leaf, and high concentrations of sugar facilitate the formation of anthocyanins. Anthocyanins do not make sugar; however, they appear to protect chlorophyll from seasonal stresses and allow photosynthesis (and, therefore, sugar production) to continue as long as possible. When cold weather and shortening day length cause chlorophyll levels to decline, bright light can inhibit photosynthesis by overwhelming the remaining chlorophyll. By absorbing some of this excess light, anthocyanins make photosynthesis as efficient as possible during the leaves’ final weeks. During this time, a major salvage operation takes place. Nutrients, including nitrogen and sugars, are moved from the leaves to the wood and roots for winter storage. In the spring, these nutrients rise again in the sap.
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Perhaps by facilitating nutrient storage, anthocyanins give some maples an edge when it comes to sap sweetness. Sugar maples are the favorite tree for making syrup because their sap has a relatively high sugar content (2 to 3 percent). Because not all leaves turn red, some trees are clearly able to complete the salvage of nutrients without anthocyanins. In Alaska, syrup is made from birch trees (whose leaves turn yellow in the fall). To make a gallon of syrup, about 40 gallons of sugar maple sap are needed versus 100 gallons of birch sap. Still, no clear relationship exists between anthocyanins and sap sweetness. Red maples achieve a brilliant crimson hue, but their sap has a significantly lower sugar content than that of sugar maples. Not all deciduous trees are useful for syrup making because of the presence of other chemicals, such as certain amino acids, in the sap. Even in sugar maples, physiological changes that occur as the tree begins to bud result in syrup that tastes “off.”
Water threads How does water get from the roots to the tops of the tallest trees, hundreds of feet from the ground, against the pull of gravity? The mechanism of water ascent in plants has generated lively debate and is an active area of research. Cohesion–tension theory, which was proposed in the late nineteenth century, still remains the most widely accepted explanation. Cohesion-tension theory holds that plants wick water from their roots to their leaves through a mechanism that is driven by evaporation and maintained by the attractive forces between water molecules. Plant anatomy meets water physics to give us our green giants, such as the California coast redwood dubbed Hyperion—measuring about 380 feet, it is the world’s tallest living thing. Water and dissolved mineral nutrients flow from a plant’s roots to its leaves through the xylem, a network of parallel pipes as fine as threads (0.01mm to 0.3mm). The pipes are made from dead cells
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aligned end to end, with the walls between adjacent cells largely removed and the outer walls heavily reinforced. As the sap flows through the xylem, water and minerals are delivered to the living cells throughout the plant. Water that reaches the leaves spreads out along the wet walls of cells within the leaf. Like a paper towel, the cell walls contain many tiny fibers of cellulose and act as an evaporating surface. Water vapor passes to the outside of the leaf through tiny pores called stomata. Stomata are also the site of entry of carbon dioxide for photosynthesis. As the water evaporates, more water is drawn from the xylem to the leaves’ evaporating surface. The fine column of water in the xylem is tugged upward as this occurs because of strong attractive forces, especially hydrogen bonds, between water molecules. Hydrogen bonds form between hydrogen atoms and oxygen atoms in adjacent water molecules through the electrical charge differences of the hydrogen and oxygen atoms. The hydrogen atoms have a slight positive charge, and the oxygen atoms have a slight negative charge resulting from oxygen hogging electrons in each molecule of H2O. The upward tug on water in the xylem can be great enough to break the column of water within the vessel, blocking flow. At night, when the stomata of most plants are closed and the upward tug ceases, root pressure can help refill the broken column. Root pressure is generated as roots actively take up mineral ions and the resulting concentration gradient causes water to flow in. When the stomata are open, the push of the water from the roots is insignificant compared to the tug on water from the leaves.
Brains over brawn The roots of trees are able to break concrete and cause lots of destruction when they are growing close to the surface. What mechanism allows these large forces to manifest themselves?
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Heaved sidewalks and punctured pipes, not to mention botanically themed horror flicks, make it easy to imagine roots as unyielding battering rams. Yet the ability to penetrate hard-packed soil and other barriers owes much to roots’ exquisite sensitivity to their environment. Roots detect and integrate a cacophony of signals about environmental factors, including gravity, moisture, light, nutrients, temperature, carbon dioxide, oxygen, bacteria, fungi, and texture. When the tip of a growing root encounters a combination of desirable and undesirable signals, it responds in a hierarchical manner. For example, exposure to a toxic level of metal ions can prompt a root to ignore gravity and thrust itself into the air. Environmental signals lead to complex chemical conversations within root tips. The conversations involve proteins, ions, pH changes, and plant hormones, and ultimately tell the root tip which direction to turn. In a bout of tree versus sidewalk, roots seem to use their super senses to find an opponent’s weakness before turning on the brawn. In a study of sidewalk cracks, a number of cases were documented in which roots had grown to a sidewalk and had followed the edge to a failed joint before growing beneath it. Soil under cracked sidewalk blocks has a higher oxygen concentration than soil under intact blocks, which may contribute to root growth under existing cracks. As it grows, the very tip of a root—the root cap—protects the root because the outermost cells—the border cells—are continually sloughing off and being replaced. Removal of border cells quickly induces cell division in the root tip to replace the lost protective layer. A mucouslike substance lubricates the cap surface interior to the border cells and decreases frictional resistance to soil penetration. Friction occurs between the border cells and soil, but the lubricated root within glides forward as the border cells are released from the root cap. Expansion of cells in an elongation zone pushes the root tip forward. By restricting the diameter of their water vessels and reducing cell layers, roots can creep into pores or slits that are narrower than the roots. On the other hand, if a root is mechanically impeded, cell growth slows. Cells thicken and increase the diameter of the root, and reinforcing fibers are laid down in the cell walls. These changes help the root apply more force and resist buckling.
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Tricking trees If tree roots can break through concrete and we understand the mechanism for how this happens, can’t we use this information to control tree root growth or deflect it to reduce the damage roots cause? Installing root-deflection devices, such as downward-sloping physical barriers to encourage roots to grow to deeper soil layers, is a common practice. Barriers may be impregnated with herbicide to inhibit or deflect root growth. Unfortunately, trees are finicky. If roots encounter soil that is compacted, the roots will grow upward once they extend beneath the barrier. Deeper soil layers are deliberately compacted to support sidewalks and other structures. Instead of penetrating the compacted soil, roots often sneak just beneath the sidewalk, where the granular nature of the sand-gravel base has small voids. Because roots do less damage if they pass deeper beneath the sidewalk, one preventive strategy is to modify this base layer. Mixtures of soil with gravel that has been coated in a small amount of gel to prevent the stone and soil from separating during installation can allow root penetration while providing adequate load bearing.
Roses are red Why is it necessary to dye roses to get blue ones? Roses seem to come in just about every other color. Why aren’t there any blue roses? Hundreds of varieties of purportedly blue roses have been commercialized, including Blue Heaven, Blue Moon, Rhapsody in Blue, Blue Bajou, and Shocking Blue. The flowers are pretty shades, such as lilac, magenta, or grayish purple, but only an optimistic rose breeder would call them blue. True blue roses are so challenging to make and so desirable that they have been called the Holy Grail of horticulture.
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Wild roses come in white, pink, and red. Over hundreds of years, mutation, selection, and hybridization have created garden roses in a variety of shapes and sizes and extended the color palette. For instance, yellow roses made their appearance in 1820. Blue roses are elusive because delphinidin, the main pigment that produces the blue hue, is not naturally found in roses. The main purpose of flower pigmentation is to allow pollinators to identify flowers against their background. The palette Mother Nature uses to paint the flowers of a particular species determines what pollinators are attracted, because different species of pollinators perceive color differently. Red flowers are distinctive to hummingbirds but not to bees, which perceive red light poorly. Some pigment patterns are invisible to us but stand out to bees, which can detect ultraviolet light. Genetic engineering can extend a plant’s color palette more dramatically than traditional breeding techniques. Making violets red and roses blue requires new pigment genes and a pH adjustment, too. Roses have been engineered with genes that enable them to produce the pigment delphinidin. The pigment accumulated in the petals, and those roses were more blue than other roses—but not really blue. That is because the pH (acidity level) in the flowers was not ideal. The pH affects the color of some plant pigments. If you cook purple cabbage with vinegar, the cabbage becomes distinctively redder. Similarly, the vacuoles—plant cell compartments in which pigments accumulate—of roses are acidic, and in this environment, the delphinidin pigment appears more red than blue. Another factor that affects delphinidin’s blueness is the presence of co-pigments. These are molecules that stack together with delphinidin, forming a complex that is bluer than delphinidin alone. It is much easier to dump white roses in a vat of dye than to breed roses with the appropriate pigments, co-pigments, and pH, but genetic engineering is yielding novel shades while bringing blue roses incrementally closer to reality.
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Violets are blue Your explanation on why there are no blue roses reminded me of something I read many years ago: No species of flower has more than two primary colors. Is this true? I believe the same article said that plants that produce red flowers are the most advanced, and yellow and blue were the first colors produced when green leaves were modified into flowers. Pansies come in yellow, red, and blue but result from crossbreeding. Each plant species typically exhibits limited flower color, especially in the wild. Three major families of pigments are responsible for flower coloration: anthocyanins, betalains, and carotenoids. Anthocyanins can be present in the same flower species as carotenoids. Betalains and carotenoids can be present in the same flower species. In contrast, anthocyanins are not present in any of the species that accumulate betalains. Although two pigment families are mutually excluded, primary colors are not, because each pigment family contains a range of colors. Rather than being classified by color, plant pigments are grouped according to similarities in their chemical structures and the overlap in the steps through which plants synthesize them. Anthocyanin pigments can paint flowers orange, red, purple, or blue. Betalains come in yellow to orange and red to purple. Carotenoids are responsible for the yellow to orange colors in many ornamentals, including marigolds, daffodils, roses, and lilies. With red or purple pigments, carotenoids give brown and bronze hues. A combination of anthocyanins with carotenoids can yield yellow, red, and blue flowers within a single species, but a unique set of enzymes is required to synthesize each pigment. Also, color depends on the shape of the flower cells, the presence of compounds that interact with the pigments, and the pH in the compartments in the cell that store the pigments.
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Therefore, for a new flower color to arise in the wild, all the right factors must come together and confer an advantage on, or at least not be disadvantageous to, the plant. For example, in greenhouse populations of petunias, blue pH mutants arise spontaneously and are completely healthy. In contrast, no blue petunias have been found in wild populations, which suggests that blue petunias may be less attractive to pollinators. Much is unknown about the evolution of flower color, but yellow flowers very likely preceded red and blue ones. Carotenoids have been around a long time because they play an important role in photosynthesis. Betalains are restricted to one order of flowering plants and may have evolved at the same time as or after anthocyanins.
Luck of the Irish What causes the phenomenon of a four-leafed clover to occur? Alterations in the number of leaflets per stem are found in other plant species as well, but because four-leaf clovers capture people’s imaginations, we tend to take more notice of them. Variations from the normal three leaflets (to four, five, or more) may arise as a result of genetics, environmental factors, and chance. Several studies with clover and alfalfa (which is related to and resembles clover) have shown that increases in leaflet number can be passed down to the next generation. The genetic control of the trait is not fully understood, but changes in multiple genes can alter leaflet number. Environmental factors play an important role in plant development and may influence leaflet number as well. For example, one study showed that the multiple leaflet trait was more common in alfalfa plants exposed to shorter amounts of daylight than in those exposed to longer amounts of daylight. Finally, the mechanisms that maintain the geometrically regular spacing of leaves, namely chemical and physical interactions between the clusters of leaf-forming cells, are not perfect. So even given the same genes and environmental conditions, it is possible for changes in leaflet number to arise occasionally by chance. Download at www.wowebook.com
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Would you like genes with that? What are the major ecological and health dangers to genetically modified products? Genetic modification of plants is not new. Around 7,000 years ago, Central American farmers developed corn from teosinte, a wild grass with tiny cobs and tough kernels, by selecting and cultivating seeds from the best teosinte plants each year. Nearly everything we eat has been modified by selectively crossing two parent plants and choosing offspring with the desired characteristics. Many generations of crossing and selection may be required to achieve the desired result, and different species cannot usually be crossed. On the other hand, modern biotechnology makes it possible to introduce a single gene from any organism into a plant. Genetic engineering is a powerful tool in agricultural scientists’ never-ending struggle to combat new plant diseases and insect pests, and to reduce the environmental impacts of agriculture. Even crossbreeding has unexpectedly yielded toxic plants, but introducing genes from unrelated organisms raises additional concerns about allergies. For example, a “high-protein tomato” containing peanut genes could trigger an allergic response in an unsuspecting tomato lover with a nut allergy. For this reason, the Food and Drug Administration mandates that new plant varieties introduced by genetic engineering be evaluated for their potential allergenicity. Another health risk concerns “pharm crops” that produce drugs to be extracted and processed into medicines. A report by the Union of Concerned Scientists recommends that drugs not be produced in crops usually grown for food. As revealed in 2000, when corn approved only for animal consumption found its way into a plethora of products on grocery store shelves, segregation would likely be insufficient to keep your breakfast cereal free of the latest meds. Corn that produces its own insecticide garnered the most negative publicity of any genetically engineered crop following a laboratory
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study that showed monarch caterpillars died when fed milkweed, their usual food, dusted with pollen from the engineered corn. Ironically, few reports mentioned that it is common practice to spray corn (genetically engineered or not) with pesticides many times every growing season. Even more ironically, the insecticide produced by the genetically engineered corn is permitted for use on organic crops. The insecticide, Bt, which is produced by a common soil bacterium, is safe to vertebrates and, unlike most pesticides, kills insects only if they eat it. All agriculture has an impact on the environment, and no technology is a panacea. The risks and benefits of each new crop must be evaluated in the context of its alternatives, as well as in the context of the local ecology in which it will be grown. Incidentally, the controversy over genetically engineered food is having an unexpected benefit: intensifying discussion about and research on the impact of all forms of agriculture on ecosystems.
Hot coral Are recent concerns about coral reefs not being able to stay apace with rising sea level unfounded? In Panama’s gulf on Isla Contadora last year, we were stunned to find huge coral reefs alive and well where tidal range is more than 20 feet, in water so hot that it almost felt scalding upon entry. If El Niño caused “bleaching” due to excessively high temperatures, we failed to find any evidence of it. Your question identifies two possible threats to coral reefs, both of which are linked to global climate change: rising sea level and increase in sea water temperature. Sea level rise itself is not expected to devastate coral reefs. Larger waves may cause erosion of less protected reefs, but rising sea level also permits reefs to expand vertically. On the other hand, temperature increases can lead to mass bleaching, as occurred in 16 percent of the world’s coral reefs in 1998, an El Niño year. Mass bleaching is believed to be a relatively recent phenomenon. Since 1979, there have been six such events.
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Bleaching occurs when the individual coral polyps, the organisms that produce the limestone skeleton of the reef, lose the algae they harbor. The algae, called zooxanthellae, give the reef its color. The zooxanthellae also produce oxygen and food the coral need, in return for the coral’s nutrient-rich waste products. Although coral can recover after mild bleaching, the sensitivity of coral to temperature changes has led scientists to predict that half of the world’s coral reefs could be lost by 2030. Research has since shown that at least some bleached coral can recover by partnering with a more heat-tolerant species of zooxanthellae. Coral reefs therefore seem to have some adaptability to climate change that scientists have not factored into their predictions. Still, much uncertainty remains regarding the combined impact of temperature changes and other threats to reefs. For example, sewage damages coral by facilitating the spread of diseases. Also, carbonic acid produced as levels of carbon dioxide in sea water increase can weaken coral skeletons.
Cold coral Why aren’t there coral reefs in San Diego? There are plenty of rock reefs, but I have never seen coral. Most people associate coral reefs with tropical paradises and warm ocean waters. (Readers from the Great White North may be raising their eyebrows, thinking San Diego is a tropical paradise, but even in summer, the water temperature is bracing!) Nevertheless, cold-water coral reefs exist, and recent studies suggest that they may cover more square miles of ocean floor than warm-water reefs. According to Nancy Knowlton, director of the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography, fast-growing reef corals need warm water because zooxanthellae, the algae that partner with the coral and produce food via photosynthesis, can live only within a narrow temperature range. Cold-water coral species lack zooxanthellae and are therefore dependent on the edible morsels that ocean currents bring their way.
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These coral species grow approximately ten times more slowly than their warm-water counterparts, but they can form spectacular reefs. Cold-water corals in the North Pacific range from Alaska to Baja, including the waters off San Diego. Knowlton explained that we do not usually see them washed up on the beach or while we are snorkeling because they tend to be found in very deep water (more than 600 feet). Unlike warm-water corals, they do not need to be close enough to the surface to obtain sunlight for photosynthesis. Small, solitary cup corals can be found in shallow water, but they are not very conspicuous. The first records of deep-sea (cold-water) corals date back more than a century, but much remains to be learned about their range and distribution, growth rates, and ecological roles. It is becoming apparent that they provide an important habitat for fish and other marine life, and concern is growing over threats to their survival, such as bottom trawling by commercial fisheries.
Festive fungi If I slack off in my housecleaning, I notice a pinkish mold buildup around the tub drain, an orangish mold around the bathroom sink drain, black mold in the bathroom sink overflow hole, and black mold growth around the metal rim of the kitchen sink. What is the significance of the mold’s color? How concerned should I be about the presence of mold in my home? Mold is a member of the kingdom fungi, which may have more than one million species, most still to be discovered. Besides the molds that show up around the house or on forgotten leftovers in the fridge, we are all familiar with many species of fungi, including those found on rotting logs, the mushroom selection at the local supermarket, the yeast that leavens our bread, the molds used in the processing of cheeses (for example, Roquefort and Brie), and fungal infections such as athlete’s foot. Under a microscope, most molds resemble skinny mushrooms. They have threadlike roots, long stalks, and spores forming at the end of the stalks. Spores are like seeds, and they often give the mold its
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color. The color can also come from waste products or chemicals molds make to digest their food. These chemicals also give mold its musty smell. Different species of mold are different colors, and molds may change color as they mature. For example, bread mold starts out white but turns bluish-green as it forms spores. Individual spores cannot be seen with the naked eye. They float through the air and germinate on moist surfaces. Fungal growth also requires nutrients. Yeast commonly colonizes an area first because it can grow even if nutrients, such as soap scum, are low. Mold can then grow on the products accumulated by the yeast. Spores from mold and other fungi are everywhere indoors and outdoors, making them impossible to avoid. Furthermore, mold growth is not always obvious. For example, one study found many different species of fungi in pillows. Water damage may also cause mold to grow within walls. Extensive mold growth, such as that associated with significant water damage, is a health concern. It can worsen asthma and allergies, although the jury is still out regarding whether it causes or just aggravates pre-existing respiratory conditions. Some molds also produce toxins—mycotoxins—that may irritate the lungs or lead to skin reactions. Controlling moisture by repairing leaks, insulating pipes to reduce condensation, and increasing ventilation is critical to reducing the growth of mold. Information on mold cleanup can be obtained from the Environmental Protection Agency Indoor Air Quality Information Clearinghouse (www.epa.gov/iaq/molds).
Wind in the willows One evening, a group of friends and I were sitting in a garden that had several leafy trees and bushes. One of the leaves on a bush began to move as though it was being hit by a light breeze, though no breeze was apparent to the onlookers. Can you tell us why this solitary leaf may have moved?
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Gusts of wind usually penetrate plant canopies on large, coherent scales, says Dennis Baldocchi, a University of California, Berkeley professor of biometeorology (the study of interactions between atmospheric processes and living organisms). Therefore, you would normally expect to see a bunch of leaves moving at once. Yet localized regions of wind turbulence might lead to the effect you describe because leaves and stems of a tree break down large eddies of air into smaller eddies. Also, similar to a guitar string, plants oscillate at the natural frequency of their stalks. Furthermore, the differences in individual leaves’ size, shape, texture, and orientation influence the way they move in a breeze.
Long-life fruit Are the oranges and blackberries growing in my backyard considered to be “living?” If these fruits are living, are they considered to be dead after they are picked? Growth, metabolism (using and transforming energy), response to the environment, reproduction, and motion (at least, internal motion) are the five characteristics that something must exhibit at some point during its existence to fall under the traditional definition of alive. Several other definitions of life have been proposed, because, under the traditional definition, fire could be considered alive, but mules (which usually cannot reproduce) would not. Plants, including their fruit, are considered alive under the traditional definition and others. The movement of fluids within plants satisfies the “motion” condition. Also, some plants can move: Sunflowers turn to face the sun, Venus Flytraps snap their leaves closed on unsuspecting insects, and Mimosas become limp when touched. When picked, fruit eventually ceases to meet the five criteria of being alive. Yet the seeds in the fruit can be considered to satisfy the definition of being alive because they have the potential to give rise to a new plant. As any gardener knows, seeds can die if stored for too
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long or under the wrong conditions. However, some seeds have the ability to remain alive (though dormant) for exceptionally long periods of time. Recently, a 2,000-year-old Judean date palm seed was coaxed into producing a seedling, dubbed Methuselah. It is the oldest seed known to have produced a plant.
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4 Funky phenomena Green eggs and ham What causes the outside of the yolk of hard-boiled eggs to turn green? The green color is iron sulfide. It is produced when iron from proteins in the egg yolk reacts with hydrogen sulfide from proteins in the egg white. Special proteins in the yolk store the iron because a developing chick needs it. Sulfur is found in certain amino acids—the building blocks of protein. Proteins in the egg white are particularly rich in sulfur-containing amino acids. Cooking breaks down some of the proteins in the egg, causing the white to release hydrogen sulfide and the yolk to release iron. These two chemicals react where they meet. Using newer eggs and cooling the eggs rapidly after cooking can minimize greenness, which, as Dr. Seuss’s Sam-I-Am can tell you, is perfectly harmless.
Just like Mama made When you buy pasta, the package instructions often tell you to add salt after the water is boiling. When you do this, some sort of reaction occurs with the water and a cloudy “pouf” rises to the top. What is this reaction? If you add more salt after this reaction, why doesn’t a second reaction occur? Why should we add the salt after the water boils?
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Water boils when water molecules are jiggling fast enough to separate themselves from the liquid to become a vapor. As you heat the water, tiny bubbles of water vapor begin to form. They fuse together into larger bubbles that rise to the surface. It takes energy for the little bubbles of water vapor to fuse into big bubbles. When you throw salt into water that has just started to boil, the salt crystals provide convenient surfaces that attract the little bubbles and reduce the energy needed for them to fuse. The “pouf” you see are the bubbles of water vapor making it to the surface. Because a limited amount of water vapor bubbles are available to fuse, adding more salt may not cause a second “pouf.” Incidentally, fine sand would also cause this reaction, but then your pasta might be all gritty instead of al dente. The pasta instructions are not telling you to add salt to create bubbles. Salty water boils at a slightly higher temperature than nonsalty water. Why? The water molecules jiggle and bump into each other until they can escape as a vapor. In salt water, the concentration of water molecules is less than it is in pure water, which means fewer water molecules exist at any surface where a bubble of water vapor might form. Salt—or, more precisely, sodium and chloride ions—gets in the way of the water molecules trying to escape. You can add the salt before you heat the water if you want. Just be careful not to add the salt when the water has heated to the boiling point but has not yet started to boil. The rapidly formed bubbles of water vapor could boil over. You can also skip the salt. A pinch elevates the boiling point by only the tiniest fraction of a degree. I am usually too lazy to add salt, and my pasta turns out fine.
A girl’s best friend I understand that the refractive index is 2 in a diamond. And if this index is used to divide the speed of light, it will show the speed of light while it is in the diamond. Is this what makes a diamond sparkle?
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When light passes from air into a more optically dense material, such as water, glass, or a diamond, it slows and bends. A material’s refractive index is defined as the speed of light in a vacuum divided by the speed of light in the material. At 2.4, the refractive index of a diamond is considerably greater than that of water (1.3) or glass (1.5). The high index of refraction has two key ramifications. First, it means that diamonds have a very low critical angle (25°), the angle above which light reflects internally. A diamond’s sparkle results from light bouncing off many of the diamond’s internal surfaces before striking one with a low enough angle to escape. Second, the strong bending of light separates it into its component rainbow of colors, giving the diamond its colored flashes, or fire. The number cited as a material’s refractive index is the average for the different colors, or wavelengths, of light. White light includes all the colors in the spectrum, and each wavelength of light has a slightly different index of refraction. As a result, when white light enters a more optically dense material, light’s rainbow colors disperse in speed and direction. Not only does a diamond have a very high index of refraction compared with other materials, but it also has a particularly high dispersion, the difference in the refractive indices for the shortest and longest wavelengths of light. The considerable dispersion can cause more blue light to emerge from one facet, and green or red light to emerge from another. All diamonds have the same refractive index and the same dispersion, but fire varies because it also depends on the gem’s shape. Fire is enhanced when the light enters and exits the diamond at sharp angles, when the path within the diamond is lengthened by many internal reflections, and when the light interacts with the junctions between two or more adjacent sides—facets—of the diamond. All these factors cause the beam of light to fan out, and all are affected by the diamond’s cut and proportions. Fire also changes with the ambient light conditions. Under diffused lighting, in which light enters the diamond from all angles, fire is suppressed because so many different beams of light are present that the colors recombine into white light as they exit the diamond. Fire is best observed when a diamond is illuminated by a single bright point source, such as candlelight.
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Hot stones I know that granite can emit radiation, which has concerned some people who have granite countertops in their homes. Do the semiprecious stones used for jewelry also emit some radiation? Nearly everything produces at least small amounts of ionizing radiation—radiation energetic enough to dislodge electrons from atoms. Semiprecious and precious stones can emit ionizing radiation, and their radioactivity may be increased by procedures used to enhance gem color. More than 50 naturally occurring radioactive isotopes are present in Earth’s crust. The main ones are radioactive isotopes of uranium, thorium, and potassium. These three radioactive isotopes and others occur naturally in minerals and gemstones. In addition, radiation produced in the laboratory is used to enhance the color of a wide variety of gemstones. Irradiation treatments are controlled versions of natural processes that occur in Earth’s crust when gem deposits are exposed to radiation from surrounding rocks. Irradiation can produce smoky quartz from colorless quartz, amethyst from iron-containing quartz, dark pink or red tourmaline from light pink ones. Irradiation also gives various colors to colorless zircons, tourmaline, spodumene, scapolite, fluorite, beryl, corundum, and diamond. Topaz is by far the gem most commonly radiationtreated, with tens of millions of carats irradiated each year. A common misconception is that when a substance is exposed to radioactivity, the substance itself becomes radioactive. Only if irradiation perturbs the nuclei of atoms within the substance will the nuclei undergo radioactive decay. One of the three commonly used laboratory irradiation procedures, exposure of gemstones to gamma rays from radioactive cobalt, does not increase a gemstone’s radioactivity. However, the other two major forms of gemstone irradiation, bombardment with electrons in a linear accelerator and bombardment with neutrons in a nuclear reactor, can make gemstones radioactive. These methods are used for gemstones that require higher doses of radiation to achieve the desired color, such as deep blue topaz.
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In the United States, the Nuclear Regulatory Commission (NRC) requires that an NRC-licensed distributor perform the initial distribution of gemstones irradiated in a linear accelerator or nuclear reactor. The distributor must determine whether residual radioactivity falls below regulatory limits. Typically, the stones are set aside for a few months to allow radioactivity to decay. An NRC fact sheet states that irradiated gemstones currently on the market are safe. Incidentally, other studies have concluded that granite countertops are only a minor source of radiation. In contrast, the average amount of ionizing radiation to which the public is exposed from medical tests has increased sevenfold since the 1980s and is now the largest source of radiation exposure.
Metal eater Why is salt water so bad for metals if you do not remove it right away? In Ray Bradbury’s short story “A Piece of Wood,” everything made of metal begins to disintegrate into tiny particles of red rust. In the story, a young sergeant intent on ending war unleashes a machine that can give metal a “nervous breakdown.” Bradbury’s inspiration could have been reality. Corrosion costs the United States about 3 percent of the gross domestic product. The chemical reactions that cause corrosion are characterized by the loss and gain of electrons. One common form of corrosion— galvanic corrosion—occurs when two different metals are in contact in sea water. Electrons flow from one metal (such as iron) to the metal that is better able to attract electrons (such as copper). The metal that gains the electrons—the cathode—passes them on to hydrogen ions and dissolved oxygen in sea water. The reaction at the cathode forms H2O, or water. The metal that loses electrons—the anode—forms positively charged ions that can undergo additional reactions, depending on the conditions. In an environment with plenty of oxygen, the sequence of reactions creates rust on iron. In low-oxygen conditions, iron may
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react to form green or black magnetite. Because iron atoms are leaving the surface at the anode, a pit forms beneath the rust or magnetite. Iron also corrodes when exposed to the moisture in air, but it corrodes ten times faster in sea water. In pure water, the transfer of electrons from one metal to another slows as positive charge builds on the anode. Sea water contains chloride ions and other ions that conduct electric charge through the solution. The ions neutralize the charge at the anode. Galvanic corrosion can occur within a single type of metal. Metals are rarely completely pure—most contain inclusions of other metals. Sea water also contains salts of other metals. Therefore, at each site that contains impurities in the metal or the water that is in contact with the metal, a tiny anode and cathode can arise. Localized changes in pH occur as metals corrode, causing calcium carbonate that is dissolved in sea water to precipitate and form a crust on the metal. In addition, bacteria, especially those that metabolize sulfates present in sea water, cause side reactions that accelerate corrosion in low-oxygen environments, such as the deep seabed where the Titanic rests.
Wet weave Why do fabric and other items get darker when (clear) water is applied? When a light beam interacts with fibers of fabric (or another substance), some light is absorbed and the rest is reflected. In wet fabric, the water in the tiny pores between the fibers refracts, or bends, light. Therefore, instead of the light reflecting from the fabric to your eye, it passes through another fiber, where a little bit more of the light is absorbed. This can happen multiple times, causing the light reaching your eyes to be dimmer and the fabric to appear darker.
Fade away Why do items that are left in the sunshine bleach or fade?
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The capability of a pigment to absorb certain colors and reflect others depends on the nature of the chemical bonds between the atoms that constitute the pigment molecule. The sharing of electrons between atoms bonds them together. Light from the sun, especially the higher-energy ultraviolet radiation, excites electrons and can break the bonds in the pigment. This process is not limited to pigment molecules; textiles, plastics, wood, and other materials also degrade over time as sunlight causes the chemical bonds in them to break.
Bleach blonde How does hair get bleached by the sun? The pigment melanin gives hair its color. It is deposited within the hair by cells called melanocytes, which are found in the root of the hair. The two main types of melanin are eumelanin (brown-black) and pheomelanin (yellow-red). On average, 3 percent of a hair’s weight is melanin. Sunlight bleaches hair because it degrades melanin. Melanin absorbs some sunlight and also captures free radicals that are produced when UV radiation falls on other proteins in hair. Melanin helps protect the other hair proteins, but melanin itself is damaged and loses its color.
Bubble geometry Why can’t we make square soap bubbles? The skin of a bubble is a thin layer of water sandwiched between two layers of soap molecules. The soap molecules have hydrophilic— water-loving—heads that face inward and interact with the water molecules. The tails of the soap molecules are hydrophobic—waterhating—and face outward. Because the water molecules and the heads of the soap molecules are weakly bonded, and the soap molecule tails also interact with each other, the soap film resists stretching.
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Therefore, unless you use some sort of scaffold for support, the skin of the bubble shrinks to the smallest possible surface area. For the same volume of air, a sphere has a smaller surface area than a cube.
Pure as rain Rainwater is supposedly pure, with no chemicals, such as those found in tap water. Because rainwater comes from the ocean, what happens to all the chemicals found in ocean water when it evaporates to become rain? Rainwater does come mainly from the ocean, because 86 percent of global evaporation occurs over the ocean. The chemicals found in sea water, which include sodium, chloride, and smaller amounts of every naturally occurring element, are left behind when water evaporates. The accumulation of scale in your humidifier, tea kettle, or a glass of water allowed to evaporate is a result of the same process. Despite popular belief, rainwater is not exactly pure: It picks up compounds from the atmosphere, including dust, algae, and soil microbes blown by the wind; nitrogen and sulfur compounds from industry, traffic, and the burning of vegetation; salt from sea spray; and even insects. Rainwater compositions vary according to land use practices and other human activities, regional geology, and local climate.
Don’t lick the railing in winter I can understand that some items (such as cotton sheets, a full plastic bottle of water, and a rubber resistance band) at room temperature are not warm because they don’t generate heat the way the body does, but why do some things feel much colder than others? Young people studying heat and temperature will initially deny that their wood or plastic desktop is the same temperature as the
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metal legs of their chair; they strongly believe that how hot or cold an object feels is a good measure of its temperature. Heat also befuddled eighteenth-century scientists, who considered it to be a massless, odorless, tasteless, transparent fluid that flowed from hot to cold objects. Scientists now understand that heat is energy transferred from one body to another. Heat isn’t a substance, but our temperature estimates are based on how well energy “flows” from an object to our skin, or vice versa. When someone’s hand at body temperature contacts an object at room temperature, molecules in the skin collide with and transfer energy to molecules in the object. These molecules vibrate faster and collide with their slower-moving neighbors, which speed up and collide with their neighbors. These collisions transfer the energy of thermal motion along the object. This process is known as conduction. A material’s thermal conductivity depends on its density and molecular bonding. Air, most fabrics, and wood are among the poorest conductors, and metals are the best. Water, concrete, rubber, and plastic fall between the extremes, with each material’s characteristic thermal conductivity determining how cold it appears to the touch (if it is less than body temperature) or how hot it seems (if it is more than body temperature). On the other hand, conduction does not typically make a large contribution to how hot or cold we feel overall. It is only one of four ways that humans lose heat to the environment. The others are emission of infrared radiation, convection via air currents, and evaporation of sweat. Conduction, convection, radiation, and evaporation determine only the speed of energy transfer, not how much energy it takes to increase the temperature of an object. The amount of energy required is determined by a material’s specific heat—the amount of energy per unit mass required to raise the temperature of the material by one degree. Water has one of the highest specific heats of any substance, a property that has many practical implications. For example, large bodies of water have a moderating effect on climate; water is an effective coolant in radiators, and moisture in the respiratory tract protects cells by warming cold inhaled air.
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Icebox paradox Why does hot water freeze faster than cold? It may seem impossible, but sometimes hot water does freeze faster than cold water. The key word is sometimes, which makes the phenomenon very puzzling. Aristotle made the earliest known reference to it in 350 B.C. It was documented and discussed until the seventeenth century, but then forgotten as modern notions about heat, temperature, and energy were developed. In the 1960s, Erasto Mpemba, a high school student in Tanzania, reintroduced the phenomenon to the scientific community. He initially observed the “Mpemba effect,” as it is now known, while making ice cream with his fellow students. He placed his boiled milk mixture into the freezer without waiting for it to cool and later observed that it froze before the mixtures that had cooled before being placed in the freezer. Many confirmations of the Mpemba effect have since appeared in scientific journals, along with a plethora of possible explanations. For example, hotter water evaporates more quickly than cold. A smaller mass of hot water can freeze more quickly than a larger mass of cold water. Although evaporation can explain the Mpemba effect in some cases, it cannot explain why the effect has also been observed in experiments using sealed containers. The Mpemba effect may also occur because the freezer floor contains frost or ice. The container of hot water melts some of the ice beneath it and settles into the ice. Tighter contact between the container and the ice improves heat loss from the water. Again, this factor may explain some everyday observations of the Mpemba effect, but most experiments published in scientific journals used thermal insulators to prevent it from playing a role. The composition of the water is a factor. Natural waters contain various dissolved mineral salts. Some of these precipitate out when the water is heated. Although small amounts of impurities help to seed the formation of ice crystals, larger amounts make freezing more
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difficult. Because heating removes some of these impurities, it may cause heated water to freeze faster than cold water. Scientists have not determined why the Mpemba effect is observed in some experiments but not others. What seems like a simple problem depends on many factors and combinations of factors: the initial temperatures of the hot and cold water and their surroundings; air currents in the freezer; the shape and material of the containers, which influence thermal currents and heat loss; and the composition of the water. Science fair project, anyone?
Ice pimples Sometimes when I make ice cubes, I get these weird icicle shapes that look like miniature stalagmites on top of some ice cubes. What causes this? The expansion of water as it freezes produces these formations. A layer of ice first forms on the surface of the water, and the pressure caused by the expansion of the remaining water as it freezes can cause fractures in the surface layer of ice. When this happens, unfrozen water can be pushed through the fractures to the surface, where it freezes. If the temperature in your freezer is not too low, such that the ice cubes do not freeze solid too quickly, liquid water can keep getting forced through the fractures, and miniature icicles are pushed upward.
Crystal triggers A 1-liter glass bottle of sparkling water looked normal when it arrived at our table, but within 8–10 seconds of being opened, most of the water turned to ice. It solidified from the top and worked its way down the bottle. Why does this occur? It may have occurred because opening the bottle relieved some of the pressure on the water. Water at normal atmospheric pressure freezes more easily than water under pressure because water expands
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when it freezes. In ice, the H2O molecules are held apart (and together) in an ordered, latticelike structure. On melting, this structure partially collapses, so liquid water takes up less space. Pressure is not the only possible explanation. The rapid freezing phenomenon can also occur with nonsparkling water, sometimes simply after tilting the bottle. It occurs because water can be supercooled—the temperature reduced to less than 0°C or 32°F without freezing—if the water molecules lack a surface, also called a nucleation site, on which to form crystals. A small particle in the water, or a rough surface on the bottle, can serve as a nucleation site. Tap water usually has plenty of impurities, but distilled water in a very smooth bottle can become supercooled without nucleation sites. Tilting the bottle may allow the water to contact a scratch or a tiny piece of ice in the lid. When an ice crystal forms, more water molecules can pack themselves around it, and the ice grows from there.
Hoar and rime What determines the temperature at which frost forms? Intuition would tell you that it is at the freezing point. However, frost often forms at a temperature above freezing. Why? Frost does form below the freezing point of water, but standard temperature measurements are usually taken at around 2 meters (6.5 feet) above the ground. The temperature at ground level or roof level may differ by several degrees from the standard temperature reading. Sometimes the air at roof level is cooler than at ground level and frost forms on roofs but not on the ground. However, on clear nights with little wind, heat from the ground is radiated into space and cold air can pool at ground level. Frost may then form at ground level but not elsewhere. Frost formation can be erratic. Cold air is denser than warm air and tends to pool in low-lying areas. On calm nights, frost may form in valleys or hollows, but slopes remain frost-free. Frost may also form first on surfaces that radiate their heat rapidly, such as metal, glass, or rock. Download at www.wowebook.com
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During nights when the temperature drops from well above freezing to below, frost may form from the freezing of dew, but usually water vapor is deposited directly as ice. The water vapor often comes from evaporation from the soil or transpiration from plants. Therefore, frost may not form on very dry soil. Two types of frost exist: hoar and rime. Hoar frost is light and delicate and can form intricate feathers, ferns, and flowers as interlinking crystals of ice grow out slowly from the first crystals deposited. Rime frost forms when fog or clouds are blown over a surface that is below freezing. It is common in coastal mountains. Rime frost usually has a more grainy appearance and can be deposited in thick layers.
Comfy abode My mother insists that in the summer heat we should shut the house up tightly the first thing in the morning and keep it that way until the sun goes down, or at least until the worst of the heat has receded. The temperature increases during the day anyway, regardless of the state of the windows, so wouldn’t it be better to allow fresh air to circulate?
Whenever it is hotter outside, keeping the house sealed slows the heating inside. An adobe house with thick walls, tile roof, and doublepaned windows tends to stay within an average of the high and low temperatures from several days earlier. Conversely, a poorly insulated house with single-paned windows will heat rapidly even with the windows shut. Our level of comfort depends not just on the temperature, but also on the humidity and whether a breeze is present, which helps sweat to evaporate and cool us. Keeping the blinds closed to direct sunlight is a good idea. But if there is a breeze, opening the windows may make you feel more comfortable inside even if it is warmer outside. Also, fans merely circulate air; they do not cool it. Unless a source of cool air exists that a fan can move into a room, it is pointless to run a fan when nobody is in the house.
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Couch potato amusements How does a TV remote work? My wife discovered that she can control the TV on the opposite side of the room by pointing the remote into the image of the TV in her vanity mirror in front of her. Television remote controls usually transmit signals in the infrared (IR) portion of the electromagnetic spectrum. The light-emitting diode (LED) on the front of the remote sends the IR signal, which the IR detector on the front of the TV senses. Although the human eye cannot detect it, IR reflects in the mirror the same way as visible light. The IR signals sent by a remote control are sequences of on/off pulses that the detector interprets as binary code, the strings of zeros and ones in the language of computers and microprocessors. Each command (power on, mute, channel up, and so on) has its own unique binary code. When the remote sends the command signal, it also sends a short code that specifies the identity of the device for which the signal is intended. So a DVD player knows to ignore a signal from the TV remote. Garage-door openers, remote-controlled toys, Bluetooth, and other remote controls that are effective over longer distances, around corners, or even through walls use radio waves instead of IR. Radio frequency extenders for some home entertainment systems permit the remote to operate across a greater range by translating the IR signal into a radio signal for transmission, and then converting it back to an IR signal that the system can understand.
Atomic dance A science teacher once told me that heat exists everywhere on Earth. But later that year, she said that space exists between the nucleus of an atom and the electrons that revolve around it. Is there heat between the nucleus and electrons of an atom? No. By definition, heat is the transfer of energy caused by a temperature difference. Objects heat up when the atoms in them move
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more quickly. For example, a microwave oven heats food by causing the water molecules within it to rotate. Even in a block of ice in Antarctica, water molecules have some motion and could heat an even colder object. Only at absolute zero (–273.15°C) are atoms completely motionless, or so scientists predict. They can chill things down to nearly, but not quite, absolute zero. Heating can occur in three ways: conduction, jiggling atoms bopping into each other; convection, the flow of hot or cold portions of a fluid; and radiation. Electromagnetic radiation is the only way heat can be transferred through a vacuum, such as from the sun to Earth through the (almost) vacuum of space. Atoms can release infrared radiation if an electron that has been excited to a higher energy level is allowed to fall back to a lower energy level. Fission or fusion of the atomic nucleus can also release infrared radiation. This occurs not because heat is stored in an atom, but because other forms of energy are transformed into heat.
Auto ambience I recently moved into a condo a few miles from the freeway. It seems like freeway noise is louder in the evening. Is this possible or am I just imagining it? It may be “in your head,” but even if it is, you are not imagining it. Other exterior background noises from human activities are generally lower during the evening. Studies with animals have shown that the sensitivity of the auditory system increases when background noise drops below a certain level. So not only are fewer exterior sounds masking the sound of the freeway in the evening, but you are also more likely to hear the sounds, such as freeway noise, that remain. Some people have speculated that the auditory system functions this way because a sudden silence may have signaled the presence of a predator to our long-ago ancestors. To escape being eaten, it would have been advantageous to be sensitive to the slightest sound.
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Another possible explanation for the nocturnal freeway noise has to do with physics instead of biology. Specifically, it is related to the impact of air temperature on the speed of sound. Sound travels faster in warmer air. During the day, the air is usually warmest next to the ground and cooler with increasing altitude. When a sound wave is traveling near the ground, the part of the wave that is closest to the ground is traveling the fastest, and the part of the wave that is farthest above the ground is traveling slowest. This causes the wave to refract, or bend, upward, away from an observer on the ground. Temperature inversions—in which the air is coolest next to the ground and warmer higher up—can occur, especially on clear, calm nights when heat radiates from the ground into space and not much wind is present to mix cooler and warmer air. In this situation, the part of the sound wave closest to the ground is traveling slower than the higher part, causing the sound waves to bend downward. The effect of temperature inversions can be quite dramatic. Depending on your location relative to the source of the sound, sound that you wouldn’t ordinarily hear can come in loud and clear. If temperature inversions, instead of levels of background noise and increased auditory sensitivity, are responsible for how much freeway noise you hear, then you should notice variations in the freeway noise with weather conditions, for instance, warm versus cool nights.
Bad hair day When rubbed against hair, how can paper pick things up, such as a paper clip? An electric force causes this capability. In fact, the word electric traces back to the Greek word for “amber” because the ancient Greeks observed that a rod of amber rubbed with a cloth attracted bits of leaves and dust. Each atom consists of a positively charged nucleus surrounded by negatively charged electrons. Rubbing two materials together can transfer electrons from one material to the other. For example, a plastic comb strips electrons from hair. The negatively charged comb
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then attracts the positively charged hair strands. But like charges repel each other, the hairs push each other apart and stick up. A neutral object such as a paper clip can also be attracted to a charged object because the proximity of the charged object induces electrons in the neutral object to move. As a result, one end of the neutral object becomes positive and the other becomes negative. Objects charged by rubbing hold their charge for only a short time before water molecules from the air neutralize them. Water molecules have a negative end and a positive end. The positively charged ends of water molecules can accept electrons from negatively charged objects, and the negatively charged ends can donate electrons to positively charged objects. This explains why static electricity is much more noticeable on dry days than on humid days.
Boing, boing, boing Hypothetically, if someone drilled a single, perfectly straight hole through the exact center of Earth and then ludicrously leaped down it, would that person ever come out on the other side? When youngsters dig big holes in the garden or at the beach, American adults commonly ask, “Are you trying to dig your way to China?” Actually, China’s antipodes—points opposite connected by a straight line through the center of Earth—are parts of Argentina and Chile. If it were possible to dig a hole straight through the center of Earth from anywhere in the 48 contiguous United States, it would end in the southern Indian Ocean. An object dropped into the hypothetical hole to the antipode would oscillate as if attached to a spring. As with a spring, the restoring force on someone falling through Earth would be directly proportional to, but in the opposite direction of, the displacement from the center. Therefore, you would make it to the other side and then start heading back the way you came, assuming that no friction or air resistance existed, and that Earth is a sphere of uniform density (not
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all that realistic, but neither is drilling a hole through Earth’s scorching, pressurized core). It would be quite the bungee jump.
Ole timers My physics textbook stated that the speed of light was first calculated in the 1600s. It amazes me that they were able to do this with relative accuracy so long ago. Can you explain how they calculated it way back when? Ole Rømer, a Danish astronomer, made the first reasonably accurate measurement of the speed of light in 1676. Rømer had been timing the orbits of Jupiter’s inner moon, Io, by studying when Jupiter’s shadow eclipsed Io. He noticed that Io’s orbit appeared to take longer when Earth was on the opposite side of the sun from Jupiter than when Earth and Jupiter were on the same side of the sun. Rømer realized that this time lag was the extra time it would take for the image of Io entering Jupiter’s shadow to reach a telescope on Earth when Earth and Jupiter were farthest from each other, compared to when the planets were closest. The difference in distance is equal to the diameter of Earth’s orbit around the sun. Therefore, Rømer divided the diameter of Earth’s orbit—not precisely known back then—by the time lag to calculate the speed of light as 220,000 kilometers (km) per second. The actual speed of light is 300,000 km per second (186,000 miles per second).
Ultimate speed Why can’t anything exceed the speed of light? What is the restraint? What is the barrier? Objects cannot be accelerated past the speed of light because the faster an object moves, the greater its mass becomes. No, this is not an excuse to give up your New Year’s resolutions to exercise. The
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effect becomes noticeable only at extremely high speeds. As an object approaches the speed of light, its mass becomes infinite. Therefore, an infinite amount of energy would be required to accelerate something to light speed. Our everyday experience tells us that mass, space, and time are separate and absolute, which is also what physicists believed until 1905, when Einstein proposed the special theory of relativity. Its key postulate is that light travels through empty space at a speed that is independent of the speed of the light source and the speed of an observer. No matter how fast you try to race beside a light beam, it will always move away from you at the speed of light. Einstein was drawn to that conclusion because it resolved problems with Maxwell’s theory of electromagnetism, which explains electric and magnetic phenomena, including light—an electromagnetic wave. But Einstein’s conclusion opened a new can of worms. If the speed of light is absolute instead of relative to the speed of the source or observer, then space, time, and mass must be relative to one’s frame of reference. Special relativity predicts that length compresses, time slows, and mass increases in a moving object relative to a slower moving or stationary object. As utterly counterintuitive as the predictions of relativity seem, they have held up to tests. In 1971, four atomic clocks were flown around the world on commercial jets and compared to time recorded on atomic clocks at the U.S Naval Observatory. Because the speed of the planes was much less than the speed of light, the clocks had to be accurate to nanoseconds to determine whether moving clocks run slowly. Time differences were indeed recorded, and they matched the values predicted by relativity. Experiments in particle accelerators also confirm the predictions of relativity. Particles called muons that spontaneously disintegrate when they reach 2 millionths of a second in age have their lifetimes increase by about a factor of 10 when they are accelerated to 99.5 percent of light speed. Although the rest mass of these elementary particles is miniscule, they become too heavy to be pushed all the way to light speed.
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Stranger than science fiction I understand that gravity is not fully understood. Is it likely that time is less understood? Time is the most-used noun in the English language (probably because we spend too much time agonizing about having too little time), but time is still a puzzle. Until Einstein came along and burst our bubble, we used to think time ticked away predictably. One of the consequences of his theory of relativity is time dilation—the slowing of time at high speeds. Time dilation is not just a crazy result of the complex mathematics of relativity. Atomic clocks onboard the space shuttle run measurably more slowly than clocks on Earth. The difference is tiny, but time dilation becomes significant near light speed, giving rise to the twin paradox. If an astronaut could take a long voyage at near the speed of light, he would return to find that he was much younger than his earthbound twin. Length contraction is another consequence of relativity. If the earthbound twin could watch his rocket-man brother eat dinner during his voyage, length contraction would make the food portion appear smaller, but time dilation would make the meal last longer according to clocks on Earth. In other words, space and time are intimately connected in four-dimensional spacetime—three dimensions of space and one dimension of time. Some researchers have proposed that hidden dimensions of space exist—and, perhaps, even additional dimensions of time. Instead of a straight line from past to present to future, time may curve through extra dimensions of space. And the rate at which time passed in the past may have been different than the rate at which time passes today. Gravity is also full of mysteries. Newton’s law of gravitation—particles attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them—works for everyday situations. However, it was revealed to be incomplete when it failed to account for the irregularity in Mercury’s orbit around the sun. Einstein’s interpretation of
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gravity explains Mercury’s variable orbit and the bending of light around massive objects in the universe. It states that the presence of mass distorts the fabric of spacetime, and freely moving objects follow this curved path. The sudden movement of very large masses should cause ripples in spacetime—gravitational waves—but these waves have not been detected directly. More troubling is that the expansion of the universe seems to be speeding up, which implies that an unknown antigravity force exists or our understanding of gravity is flawed. Things break down on the smallest scale, too. Gravity refuses to fit into the standard model—the theory in physics that explains what matter consists of and what holds it together. So gravity is preventing physicists from having much spare time.
Universal ingredients If somehow I could collect a spoonful of electrons, what would they be made of? They have mass, so they must be made of something. Particle physicists believe that electrons cannot be divided and that they do not have any internal structure. According to the standard model in physics, the electron is 1 of 12 fundamental (indivisible) matter particle types. One day, we might learn that these fundamental particles are made of still smaller particles. After all, atom derives from a Greek word meaning “indivisible.” Atoms were thought to be the smallest particles until close to the turn of the twentieth century, when the electron was discovered. A well-known consequence of the divisibility of the atom is the atom bomb. An atom contains electrons and the nucleus. The nucleus consists of protons and neutrons. The protons and neutrons consist of quarks, which, similar to electrons, are fundamental particles. Electrons and two types of quarks—the up quark and the down quark—are the three types of fundamental particles that constitute ordinary matter.
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Feeling empty Are we mostly nothing made out of mostly nothing? If atoms are mostly space, how or why are things solid to the touch? In 1911, Ernest Rutherford fired positively charged particles at a thin gold foil. Most of the particles passed through the foil, but some bounced back. Rutherford concluded that atoms consist of mostly empty space, surrounding a dense, compact region with a positive charge (the nucleus). Despite the space that exists within atoms, the forces between the particles give substances their strength. A table supports a book because of the bonds (shared electrons) between atoms in the table’s molecules. Attractive forces hold the atoms together, but repulsive forces between the atoms’ outer electrons prevent the atoms from being pushed into one another. Things get kind of weird when it comes to explaining the forces between subatomic particles. According to the standard model, these forces are also carried by particles, which are tossed back and forth similar to a basketball between players. The strong nuclear force that binds the quarks in the nucleus is carried by particles known as gluons. Photons are the particles that carry the electromagnetic force that binds electrons to the nucleus. More intuitively, a fishnet or chain-link fence can also be very strong because of the way it is constructed—yet it is full of empty space.
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5 Environmental effects Tempest tech Why can’t the wind wall of a hurricane be zapped with lasers, disrupting the airflow and degrading these destructive monsters to just simple passing storms?
The first hurricane-modification mission, Project Cirrus, in October 1947, resulted in outraged citizens and threats of legal action. The targeted hurricane, which was heading east away from the coast of Florida before intervention, turned around and pummeled the coasts of Georgia and South Carolina. From what we know now, the turn likely had nothing to do with the intervention, but the inauspicious beginning cast a pall over hurricane-modification efforts. A couple bad hurricane years renewed interest in hurricane research and led to Project Stormfury, launched in the early 1960s. Stormfury’s goal was to study the formation, structure, and dynamics of hurricanes to improve forecasts and seek ways to modify hurricanes. Stormfury continued for 21 years, but modification attempts were conducted on only four hurricanes, in part because the region in which hurricanes could be targeted was very restricted. Cirrus and Stormfury employed low-tech “seeding.” Seeding by dumping dry ice or silver iodide into clouds can result in rain or snow because the particles provide a surface on which cloud-borne moisture can freeze. Heat is released during freezing, and the working hypothesis was that the heat produced by seeding hurricanes would disrupt airflow in the storm system and weaken its winds.
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Results consistent with the hypothesis occurred in three of the four hurricanes seeded. Unfortunately, as the researchers studied more hurricanes, they discovered that the weakening they observed in the seeded hurricanes also occurred in unseeded hurricanes. Worse, the basis of their working hypothesis turned out to be flawed. Seeding has an effect only if not enough natural ice crystals are present to act as seeds. In contrast to what the researchers initially thought, plenty of natural ice crystals are present in the hurricane updrafts and downdrafts. Computer models show it is theoretically possible to weaken or reroute hurricanes. One suggested method is to use an array of solar power stations orbiting Earth that would produce microwave beams to heat sections of a storm to perturb it. Another idea is to cool the ocean surface or cover it with a biodegradable film to reduce evaporation, starving the storm of the energy that fuels it. The sheer scale and immense power of hurricanes make any method a challenge, and although scientific understanding has advanced tremendously since Project Cirrus, hurricanes remain unpredictable. Political problems are a risk if the intervention fails or accidentally sends (or seems to send) the hurricane toward another country.
Eye of the storm Can you explain why warm water is needed to fuel a hurricane? A skyward flow of warm, moist air is required for the initiation and continuation of the storm. Consequently, warm water, usually 80°F (27°C) or warmer, provides the energy that sustains the hurricane; hurricanes diminish in strength when they pass over cold water, churn up cold water from the ocean depths, or make landfall. Warm, moist ocean air is forced aloft when air masses or surface winds converge. The air cools as it rises, causing the water vapor in it to condense. Condensation releases heat, which warms the air and causes it to rise further. To compensate, surrounding air flows outward at the top of the storm. The outward flow of air diminishes the
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amount of air in the column in which the storm is brewing, lowering the pressure at the ocean surface. The reduction of pressure at the ocean surface increases evaporation. Therefore, a chain reaction of evaporation and condensation occurs as long as the source of warm, moist ocean air is available and no wind shear exists to break up the storm. As the chain reaction continues, the temperature increases dramatically at higher altitude in the storm’s core. At the surface, wind speed increases as more air is drawn into the low-pressure area. The rotation of Earth creates a pattern of wind that circulates counterclockwise (in the Northern Hemisphere) around the center of the storm. This gives the hurricane its characteristic spiral shape of concentric bands of thunderstorms surrounding a central eye. The fiercest wind and rain occur just around the eye of the storm—in the eyewall—yet the eye itself remains a calm area because the winds swirl around the eye but do not extend into it. Since Hurricane Katrina, much discussion has centered on how global warming may affect the number and intensity of hurricanes. Increased ocean surface temperatures could support more intense storms and increase the length of the hurricane season, which currently runs from June through November in the tropical North Atlantic and North Pacific oceans. Hurricane number and intensity has increased in recent years, according to the available data, but this increase may not be “real.” Until satellite measurements began in the 1970s, hurricane data were collected with ships and airplanes, which cannot detect all storms or measure the strongest winds in the eyewall. So the apparent increase in hurricane number and intensity could be attributable to flaws in the older data.
What’s in a name? How are Asian cyclones named? I saw that TS 06W was followed by Typhoon Pabuk, with TS Wutip right behind.
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Nearly all tropical cyclones are given people’s names. During World War II, U.S. Army and Navy meteorologists informally named storms after their girlfriends and wives. The U.S. Weather Bureau adopted the policy of giving women’s names to tropical cyclones in 1953. Later, in the interest of gender equity, men got equal opportunity to have storms named after them. Now the United Nations’ World Meteorological Organization (WMO) names most storms. The WMO uses a predetermined list for each ocean basin. For most basins, the WMO uses yearly, alphabetical lists of names in the predominant languages of the countries in that region. For example, English, Spanish, and French names are used in the North Atlantic region, which includes the Gulf of Mexico and the Caribbean Sea. The naming of cyclones in the Northwest Pacific follows a different pattern. Most of the names are either Asian words for plants, animals, and foods, or adjectives; just a few are personal names. In addition, the names are not listed from A to Z, but rather in order of the contributing nations, which are alphabetized. Laos contributed the name Pabuk, which is a freshwater fish. Macau contributed the name Wutip, which means “butterfly.” As soon as the Joint Typhoon Warning Center in Hawaii detects a tropical depression, a rotating area of low pressure that may become a tropical storm, it assigns it two digits and a letter. The letter identifies the region; W stands for the western North Pacific. TD 06W was the sixth tropical depression (TD) in the western North Pacific that hurricane season. TD 06W did achieve tropical storm (TS) strength, defined as winds of 34 knots or more, at which point it should have been given a name. It retained tropical storm status for less than a day. It was then downgraded to a tropical depression, and it remained unnamed despite the damage it did. Name rosters are reused, but if a storm causes significant damage and deaths, the name of the storm can be retired as an act of respect for the victims and to prevent confusion on insurance claims. Katrina, Rita, Isidore, and Juan are just a few of the many names that have been retired (see www.nhc.noaa.gov/retirednames.shtml for a full list). The country worst hit by a storm can ask the WMO’s Regional Association to retire the name from the region and can offer a replacement name.
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Oz inspired What causes tornadoes to occur? About 800 to 1,000 tornadoes occur annually in the United States. Most occur in the center and southeast of the country, where warm, moist air from the Gulf of Mexico meets air masses from Canada or the Rocky Mountains. Tornadoes are most common in the spring and summer months, but they can happen anywhere, at any time of the year. Tornadoes usually develop from thunderstorms. Thunderstorms result when warm, humid air rises and encounters a layer of colder air. This cools the warm air and causes the water vapor in it to condense into water droplets or freeze into ice crystals. Condensation and freezing release heat, which triggers more upward air movement and adds to the storm’s power. Tornadoes form between the rising warm air and the cooler air descending with the rain or hail. The strongest tornadoes are produced by supercells, large thunderstorms with cloud structures 1,000 cubic miles or greater. Normal thunderstorms are stifled when falling, rain-cooled air cuts off the supply of rising, warm, humid air. In a supercell thunderstorm, a slowly rotating column of air called a mesocyclone prevents rain from falling into the rising air and allows the thunderstorm to last for hours. A mesocyclone develops when winds at higher altitudes blow at different speeds than those at lower altitudes, which turns the air between like a rolling pin. The upward flow of warm air in the thunderstorm can tilt this rolling tube of air from horizontal to vertical, giving birth to the mesocyclone. Most strong and violent tornadoes form within the mesocyclone. Meteorologists understand how thunderstorms and mesocyclones form. However, they cannot explain why not all thunderstorms, not even all supercells, give rise to tornadoes, or why tornadoes can be spawned by growing clouds that have not yet become thunderstorms. Preliminary evidence suggests that a fluctuating downdraft, driven by falling precipitation, may energize a tornado. The downdraft draws rotation downward and focuses it.
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A series of aptly named projects have sought to determine the exact mechanism that produces the rapid twisting of the tornado itself: Verification of the Origins of Rotation in Tornadoes EXperiment (VORTEX); Radar Observations of Tornadoes And Thunderstorms Experiment (ROTATE); and the TOtable Tornado Observatory (TOTO), the reallife inspiration for the Dorothy device in the movie Twister. TOTO never actually saw the inside of a tornado, but recently, armored probes called “turtles” have successfully measured pressure, temperature, and humidity beneath tornadoes. In addition, mobile Doppler radars are providing enhanced details of tornado features and wind speeds. With these measurements and computer modeling, researchers hope to turn out a much less cloudy picture of tornado formation.
Rain terrain Why is the western half of the Unites States mainly desert, whereas the eastern half is green from much more rain? Texas is actually split down the middle—desert and green. Across the United States, average precipitation is high in the East and Northwest, moderate in the middle of the continent and very low in the Southwest. Geographic precipitation patterns depend on proximity to water, local topography, distribution of air masses, and global pressure systems. The Pacific Northwest’s famously wet weather is due to the prevailing winds forcing moist maritime air masses to undergo orographic uplift, rise up a mountain slope. As the rising air masses cool, the moisture in them condenses and drops on the windward side of the Rocky Mountains. After the air masses pass over a mountain, they descend and warm, creating a rain shadow on the mountain’s lee side. Because the Rockies run from north to south along the western part of North America, perpendicular to the prevailing winds, the central part of the continent is relatively dry. In contrast, in Europe,
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maritime air masses can penetrate deeper into the continent because the major mountain chains are oriented east–west, parallel to the prevailing winds. The U.S. Southwest is dry for the same reason a belt of deserts circles the globe at approximately the same latitude, near 30° north and south. These deserts include the Mojave, Sonoran, Sahara, and Arabian deserts in the Northern Hemisphere, and the Atacama, Kalahari, and Australian deserts in the Southern Hemisphere. These deserts coincide with high-pressure systems—the subtropical highs—caused by sinking air masses that are part of global air circulation patterns. Hot air rises at the equator and sinks at higher latitudes. Subsiding air inhibits precipitation as it warms and evaporates moisture, and by suppressing uplift of other air masses in the region. The subtropical high shifts poleward as the sun’s elevation increases in the spring and equator-ward as the sun’s elevation declines in the fall. The north–south shift brings dry summers and rainy winters to regions on the poleward edge of the subtropical high. In the Southeast, air masses passing over warm Gulf Stream currents provide a source of moisture when they blow onshore. Uplift induces precipitation as these air masses pass onto land. Precipitation also occurs across the eastern half of the United States as these warmer air masses move inland and clash with polar air masses from Canada.
Blowin’ in the wind Earth rotates at about 1,000 miles per hour eastward. Therefore, one would think that the jet stream would blow from east to west. However, it doesn’t. Why this contradiction?
The atmosphere rotates along with Earth; therefore, the jet stream is not analogous to the wind in your face as you speed along on a bike or in a convertible. If it were, the jet steam would be strongest
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at the equator, where Earth’s surface is farthest from the rotation axis and spins the fastest. In reality, early mariners dubbed the equatorial region “the doldrums” because it lacks prevailing winds. Jet streams are generated by differential heating of Earth’s surface. Because of the tilt of the Earth, higher latitudes receive less solar radiation than the tropics. The distribution of solar energy received by each hemisphere changes from summer to winter, altering the strength and locations of the jet streams. The gradient of incoming solar energy creates pressure gradient forces and sets up a north–south conveyor belt of air masses. Air near the equator rises as it warms, creating a region of low pressure. The warm air from the equatorial region flows at high altitudes toward the poles. Partway there, the air cools and descends. From this high-pressure zone, air flows to the low-pressure zone at the equator, completing the north–south loop. This large-scale overturning of the atmosphere is called the Hadley Circulation. In both hemispheres, two additional smaller circulation loops exist between the Hadley Circulation and the poles. The temperature gradient between the equator and the poles is not even. The jet streams, which are typically eastward-flowing rivers of wind miles above Earth’s surface, form along boundaries between air masses with the greatest temperature contrast. The Coriolis effect, an indirect effect of Earth’s rotation, causes these winds to flow west to east. An air mass rising over the equator has the same west-to-east motion as the ground beneath it. As the air mass moves northward, it still has the same west-to-east motion, but as a result (because Earth’s surface spins faster at the equator), the air mass is moving more quickly eastward than the ground beneath it. In contrast, an air mass flowing from higher latitudes to the equator has less eastward motion than the ground beneath it, so near the tropics, the winds tend to blow toward the west. Sailors have long taken advantage of prevailing wind patterns by sailing close to the equator (while avoiding the doldrums) to get from Europe to the Americas and taking a more northern route to return home.
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Turn, turn, turn It is generally believed that naturally occurring vortexes tend to rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. I heard someone say with absolute certainty that this directional phenomenon also applies to the swirl that occurs in the bowl when a toilet is flushed. My position is that the direction of swirl depends solely on the design of the toilet, not the hemisphere in which it is located. What are your thoughts in this regard? Anyone who has traveled across the equator has probably been asked to report back on toilet swirl. On my own trip to the Land Down Under, I was (nerd alert!) so intrigued by the light flush/heavy flush options on many of the toilets (a water conservation measure for a dry continent) that I forgot to study direction of swirl. Not that it matters. The direction in which water is injected into the bowl through angled tubes determines which way your business spins. That the direction toilets flush or drains drain depends on hemisphere is a myth perpetuated in popular culture, including a Simpsons episode, “Bart Versus Australia,” as well as some (usually) more scholarly sources. Like many myths, it is based on the misapplication of a real phenomenon—in this case, the Coriolis effect. It was well known by the 1800s that cannonballs fired along a north–south line in the Northern Hemisphere tended to land to the right of their direction of travel. This apparent deflection is caused by the Coriolis effect, the rotation of Earth beneath the cannonball. The eastward speed of an object on Earth is lower at higher latitudes. At the North Pole, it would have no eastward movement; it would simply spin around once per day. At the equator, an object travels in a circle the circumference of the Earth, moving eastward at more than 1,000 miles per hour. Therefore, a cannonball fired northward in the Northern Hemisphere has a greater eastward speed than
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the ground beneath it. It lands to the east (right) of where it would if Earth was stationary. The Coriolis effect is responsible for the large-scale dynamics of the atmosphere and oceans. For example, in the Northern Hemisphere, it causes air to move clockwise around a high-pressure area and counterclockwise around a low-pressure area, as in the case of a hurricane. The motion is the mirror image in the Southern Hemisphere. Nevertheless, just as one does not worry about the Coriolis effect when playing ball in the backyard, the effect is negligible on the small scale of toilets and sinks. The direction in which water was initially added and the geometry of the sink or toilet determines how it drains.
Be still, rubber ducky Isn’t standing water in a perfectly level and symmetrical basin actually slowly turning counterclockwise (in the Northern Hemisphere) due to Earth’s rotation? When the water is allowed to drain, the progressively smaller radius required for the water to flow through the drain opening requires that it increase in velocity to maintain angular momentum (think of a spinning ice skater pulling in his arms). Hence, the slow, imperceptible counterclockwise rotation of the standing water becomes much more pronounced as the water leaves the basin. If no other torques—twisting forces—are acting, one can see the effect of Earth’s rotation on the direction of swirl in a draining bathtub. Ay, there’s the rub. Residual motions from filling or splashing in the tub, air currents in the room, thermal currents due to nonuniform water temperature, the act of pulling the plug, and any lack of symmetry of the vessel outweigh the Coriolis effect. For example, by varying how the kitchen faucet is positioned as the sink is filled, it is possible to switch the draining vortex from counterclockwise to clockwise. For a small tub, the Coriolis acceleration is at least 100,000 times smaller than the acceleration due to gravity. Therefore, to detect the Coriolis effect on a draining tub, one must be very, very patient. Wellcontrolled conditions are also essential, including the use of a
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symmetrical tub to minimize torques produced by the tub’s walls, a plastic cover to eliminate the effect of air currents, a room maintained at uniform temperature to reduce thermal currents, and the ability to remove the drain plug from below. Fortunately, a Boston-based scientist by the name of Ascher Shapiro had the patience and equipment and published his results in Nature in 1962. He discovered that if the water in a covered tub was left to settle for 24 hours, the residual motions were eliminated. When the plug was carefully removed, the vortex was invariably counterclockwise even if the water was initially added with a clockwise spin. Therefore, under tightly controlled conditions, drain swirl is consistent with the Coriolis effect, but in everyday situations, the Coriolis effect is too small to influence rubber ducky’s trajectory in the tub.
Parched News reports frequently blame the Southwest’s diminishing water supply on a continuing drought. Are the news reports misidentifying an oversubscription (human demand) of Western water resources or has there really been a significant change in precipitation in the Southwest? Or are both causes contributing simultaneously?
The drought is real but not unusual. The two relatively wet decades that preceded it were more of an anomaly. A wealth of data about past climate, including lake sediments and annual growth rings of trees, reveal that periodic droughts are a normal occurrence in the Southwestern United States. The last major drought in the region occurred during the 1950s. The recent drought has been warmer than the 1950s drought and has resulted in more extensive tree die-offs. The die-offs are not constrained to places where humans are competing with the trees for ground or surface water. Compared to a drought that occurred in medieval times, however, the current drought is mild. A.D. 900 to 1400 was a period of
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successive droughts, each tending to persist for decades, compared to the multiyear or decade-long droughts of modern times. Today the demand of the colossal urban and agricultural infrastructure in the ever-growing Southwest far outstrips the water supply. In many places, groundwater extraction has dramatically lowered the water table. This has destroyed vegetation, resulted in subsidence—lowering of the ground surface—and caused sea water to intrude into coastal aquifers. Surface waters are also receding all over the thirsty Southwest. Without a decrease in water use, the Lake Powell and Lake Mead reservoirs on the Colorado River likely will be completely depleted by 2021, according to a Scripps Institution of Oceanography study. The Colorado River is oversubscribed because the water rights documents that determine the water allocations to the states of the Southwest were drawn up in the early 1900s, during a period of exceptionally high stream flow. Droughts in the Southwest are associated with periodic variations in sea surface temperatures linked to changes in ocean circulation. Most familiar, La Niña conditions—cooling in the equatorial Pacific (the opposite of El Niño)—lead to the formation of an atmospheric ridge that keeps precipitation off the Southwest. Climate in the Southwest is also influenced by periodic sea surface temperature changes farther north in the Pacific and the North Atlantic.
Or deluged? Some scientists believe Southern California will experience diminishing rainfall in the future due to global warming. I have also read that climate change will likely result in a “perennial El Niño effect” in the Pacific. Since El Niños generally increase California’s rainfall, these two predictions appear to conflict. What’s the real answer? Initially, global warming was predicted to lead to more and stronger El Niños by affecting the sea surface temperature gradient
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that drives the El Niño–Southern Oscillation (ENSO), the planet’s most prominent year-to-year climate variation. The most recent evidence suggests that a change in the ENSO is unlikely. In a non–El Niño year, the tropical Pacific is 3°F to 6°F (5°C to 10°C) warmer in the west than in the east. The warmer water in the west heats air masses and causes them to rise, generating strong rainfall in the area. The air masses then flow eastward, in the direction of the prevailing winds, and descend over the cooler water. The result is a conveyor belt–like movement of air, the Walker circulation. Strong westward surface winds complete the circulation. The winds pile up warm water in the western equatorial Pacific and stimulate the upwelling of cold water from beneath the surface in the east. Therefore, the winds and sea surface temperature gradient reinforce each other through positive feedback. During an El Niño event, there is a breach in the positive feedback. The sea surface temperature gradient declines as the water in the east warms. Global precipitation and climate patterns are impacted, including increased winter storms across the Southern United States. Consistent with global warming, tropical Pacific sea surface temperatures have increased during the past half-century. The warming is asymmetrical and initially appeared to be occurring in an El Niño–like pattern. A closer analysis, described in a December 8, 2009, study published in the journal Proceedings of the National Academy of Sciences, revealed that the latitude and extent of the warming differs from the canonical El Niño pattern. Furthermore, a comparison of 20 climate models revealed that El Niño frequency likely will remain the same during the next century. ENSO is not the only way global warming can alter precipitation patterns. Warming also increases the amount of water vapor in the atmosphere. Instead of the increased water vapor leading to uniform increases in precipitation, a “rich-get-richer” scenario appears more likely. Regions that already receive high rainfall because of local geography and air currents will likely get wetter, while drought-prone areas such as Southern California will get drier.
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Fast fashion How do we go about recycling old sheets, clothing that is no longer wearable, and towels? I cannot bear to throw them in the landfill, and I have enough rags to last the rest of my lifetime. Americans generate more than 12 million tons of waste textiles annually, constituting 5 percent of total municipal solid waste, according to the U.S. Environmental Protection Agency. This textile waste, which is from industry and domestic sources, is equivalent to approximately 80 pounds per person. As globalization has made it possible to create clothing at increasingly lower prices, textile waste has increased, with implications that go beyond disposal. For example, a quarter of pesticides used in the United States are applied to cotton crops. Fortunately, recycling of textiles is on the rise. Textile recyclers separate used clothing into categories according to type, size, and fiber content. Over half of the recycled clothes are turned into rags and absorbent pads for industrial spills or are recycled into fiber. Polyester is processed using heat, and cotton is garneted, a mechanical process that turns it back into fiber. The fibers are then used to make paper, stuffing for furniture, or insulation. The remaining clothing is exported. The Salvation Army estimates that when clothing is disposed of, it has at least 70 percent of its useful life left. Japan is the largest buyer of high-end or vintage American fashion. Cheaper clothing is packaged into 100-pound bales and shipped to developing nations. Small entrepreneurs buy the bales and sell the clothing at markets. Reuse or recycling of textiles results in considerable energy savings. For every pound of virgin cotton that is displaced by secondhand clothing, 30 kilowatt-hours (kWh) is saved, and for every pound of polyester, 40kWh is saved, when resource extraction, manufacturing, collection, distribution, and waste disposal are taken into account, according to a life cycle assessment published in the January 2006 issue of the journal Resources, Conservation and Recycling. Textile recyclers do not usually obtain clothes directly from consumers. Instead, castoffs can be donated to charitable organizations,
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such as the Salvation Army, Goodwill, or St. Vincent de Paul. Those organizations sell items they cannot use or sell in thrift shops to textile recyclers for a few cents per pound. Other potential uses for old sheets, towels, and other fabrics include packaging materials, arts and crafts, or drop cloths for painting. Items made from fur can be recycled into new animals (well, kind of) through the Coats for Cubs program run by the Humane Society of the United States (HSUS). HSUS distributes the furs to more than 200 wildlife rehabilitators across North America. Rehabilitators report that the fur “surrogate mothers” reduce stress in their injured and orphaned wildlife patients. For more information, see www.hsus. org/furdonation.
Trash or treasure? I have heard from a couple different sources that, with the exception of aluminum cans, recycling is actually bad for the environment because the resources expended in recycling are higher than those saved. What is the truth behind this concept? An accurate assessment of the environmental soundness of recycling must consider the energy required to process virgin materials versus reprocess recyclables, the air and water pollution and solid waste produced in each case, the environmental costs of placing recyclables in landfill, and the environmental costs of acquiring virgin materials. Studies suggesting that recycling is bad for the environment ignore part of the picture. • Aluminum—As you point out, the efficiency of recycling varies for different types of materials. Recycling aluminum is both economically and environmentally advantageous. According to the Environmental Protection Agency, making a can from recycled aluminum takes 95 percent less energy than making one from virgin bauxite ore. Aluminum can be recycled repeatedly, keeping it out of landfills and reducing environmentally damaging mining operations. • Paper—Recycling paper requires more water than producing paper from wood, but recycling releases fewer toxic chemicals.
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Recycling paper reportedly uses more fossil fuels, but the data are misleading because the forest products industry generally does not factor in fuel used in forest management (drilling, seeding, harvesting). Furthermore, decomposition of paper in landfill produces methane, a greenhouse gas. Some argue that because trees are replanted, harvesting wood has no environmental impact. Not true. Old-growth forests, which are cut down to make way for tree plantations, have more species of trees at mixed ages and heights, and they contain more animal habitats and, consequently, more biodiversity. Therefore, overall, recycling paper benefits the environment. • Plastic—Melting plastic to reuse in containers, plastic lumber, and so on is environmentally sensible because plastic is derived from crude oil. Unfortunately, the wide variety of plastics, additives, and dyes makes separation arduous and expensive. Currently, more than three-quarters of all post-consumer plastics end up in landfills. Efforts are underway to create practical alternatives, such as gasifying plastic—turning it into fuel—to eliminate this waste. • Glass—When glass is made from scratch (quartz sand, soda ash, limestone, and minerals), very high temperatures are required to melt the ingredients. Recycled crushed glass melts at a lower temperature, so less energy input is required when it is added to the raw materials. One complication is that window panes, light bulbs, and cookware contain ceramics and can introduce impurities. Colored glass also needs to be kept separate. Even when segregation is impractical, crushed glass is useful for drainage and building materials.
BYO bag Which is better for the environment, paper or plastic?
Bans on the use of plastic bags give the impression that paper must be the better alternative. However, if they were recycled (unfortunately, a huge if), plastic bags would be more environmentally friendly than paper. Download at www.wowebook.com
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Less energy is required to make plastic bags, even factoring in that a paper bag usually gets packed with twice as many groceries as a plastic bag. Making plastic bags contributes less air pollution and waterborne waste than making paper bags. It is a disadvantage that plastic is not biodegradable, but excavations of old garbage have shown that paper also decomposes very little under the relatively dry conditions of most landfills. The energy used to produce other plastic items, including disposable cups and plates and packaging materials, is less than the energy required to make the paper alternatives. Plastic products are lighter weight and less bulky than the comparable paper products, making them easier and cheaper to ship. The energy savings has improved over the years because the plastics industry has been “light-weighting” objects—using less material to make products that serve the same function. Sadly, a serious environmental problem is associated with plastic. Plastic debris is known to harm large numbers of marine animals, including whales, dolphins, seals, fish, birds, and turtles, which get tangled in it or eat it. Animals often selectively consume plastic items that resemble their natural prey, and the plastic can accumulate and block the digestive system. The plastic is released back into the environment when the animal dies and decomposes. Enormous trash-filled gyres—areas with heavy currents that form giant whirlpools—are scattered around the world’s oceans. Because it is lightweight, slow to degrade, and omnipresent, plastic is the most common refuse in these garbage gyres. The confettilike particles that plastic eventually degrades into over time are pervasive in the environment. Therefore, if plastic is not properly recycled, it is more environmentally harmful than paper. For environmentally conscientious consumers anywhere, carrying reusable bags is the best solution, to save resources and reduce waste. Selecting alternatives with less packaging and buying in bulk when practical also help the environment. The largest portion of municipal waste is packaging and containers, comprising nearly onethird of total waste generated. Americans generate about 250 million tons of solid waste annually (not including construction or industrial waste), according to the U.S.
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Environmental Protection Agency. That is an average of 4.5 pounds per person per day. Paper and cardboard make up 34 percent of the waste by mass, but half is recycled. Plastic accounts for 12 percent, and only a small fraction is recycled.
Trash tour Here’s a question that perplexes me every time I throw a tissue in the toilet or push vegetables down my garbage disposal. If organic matter or paper cannot be recycled, which method of disposal is the most environmentally friendly? Should we try to put as much as possible into the city sewer system and hope that the sludge it becomes will be used somehow? Or is it best to flush as little as possible and send everything off to be locked up in a landfill? A general rule of thumb is that if it makes you send more water down the drain or toilet, it is not helping the environment. Although rarely discussed in polite company, flushing accounts for more than a quarter of indoor water usage. Older toilets use up to seven gallons per flush. In 1994, a federal law created a new standard of 1.6 gallons per flush. The latest trend is dual-flush models that use 0.8 gallons of water to dispose of liquid waste and twice that for solids. Well over one-third of American homes have pre-1994 toilets. Whether one’s abode is equipped with a water-gobbling monster or an eco-throne, if it is hooked up to the city sewer system, whatever gets flushed goes to a sewage treatment plant. There, screens are used to remove toys, rags, and other large items that were inadvertently or deliberately flushed down the toilet or sent down the drain. This material is sent to landfills. Sand grit and stones are allowed to settle out and are also usually sent to landfills. The remaining liquids and solids are separated by sedimentation. The liquid is treated with bacteria that break down the biological compounds, including those from food waste, human waste, soap, and detergent. Before the liquid is released back into rivers or lakes or recycled for irrigation, it is filtered and disinfected with chemicals or with ultraviolet light.
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The sludge is also usually processed with bacteria and then treated with chemicals. The U.S. Environmental Protection Agency estimates that about half the treated sludge, referred to as biosolids, is recycled to land as fertilizer. Otherwise, it ends up in landfills, sometimes as daily landfill cover. Given that a lot of what goes down the pipes ends up in landfills after much processing, it is better to send garbage to landfills directly if it cannot be recycled, reused, or composted. Food composting is an educational family activity suitable for urban dwellers. Much food waste can be composted by red wriggler worms in a small bin.
Entertainment budget How much does it cost to watch TV? What “gotchas” should I be aware of? It depends on whether your set rivals the wall-dominating models in Ray Bradbury’s book Fahrenheit 451 or is a more modest oldfashioned type. The average power use per square inch is 0.36 watts (W) for a plasma TV, 0.27W for an LCD TV, 0.23W for one of those vintage cathode ray tube sets, and 0.14W for a digital light processing TV, according to a study by Pacific Gas and Electric. For an average-sized model, PG&E estimates that power use ranges from 101W for a cathode ray tube TV to 361W for a plasma screen. If you spend 5 hours per day glued to the set or with the TV providing background noise, average energy consumption ranges from 184 to 659 kilowatt-hours (kWh) per year. At a rate of 13¢ per kilowatt-hour, that would cost between $24 and $86 annually. For a table comparing the power consumption of 150 HDTVs, see CNET reviews (http://reviews.cnet.com/green-tech/tv-consumption-chart/). TV energy consumption has been increasing rapidly in recent years. The trend is expected to continue due to growth in sales of LCD and plasma TVs; expanding screen size; increase in daily use time; enhanced features and functionality; and electronics associated with TVs, such as cable TV and satellite tuners, digital video recorders, and game consoles.
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The Natural Resources Defense Council estimates that television viewing represents about 10 percent of residential energy consumption. To decrease energy use, your set may allow you to opt for the power-saver mode, reduce light output, choose the “home” instead of the “retail” setting, and turn off “quick start.”
Vampire appliances If you leave a room and plan to come back, is it better to leave the lights on or turn them off? I’ve heard conflicting views on this. Many people hold the misconception that switching on lights, especially fluorescent lights, requires a large power surge. This is not true. The power surge to light a fluorescent bulb requires only as much energy as the bulb would use in a few seconds of operation. On the other hand, the life of a bulb is diminished by frequent switching. Trading off energy use versus lifetime of the bulb, a general rule of thumb is that it is worth turning off the light if you will be gone more than 10 minutes. When possible, consider turning off devices that consume standby power, such as satellite boxes and devices with receivers for remote controls. On average, standby power accounts for 5 to 7 percent of U.S. household energy use and increases with greater penetration of home electronics.
Light pollution Is there any way to estimate, however roughly, the amount of greenhouse gases that would be kept out of the atmosphere if everyone turned off their porch lights? Let’s assume that, on average, every household in America illuminates one 60W light bulb for 8 hours per night. Over the course of a year, each household would use 175kWh to keep the porch lights on. According to the American Community Survey, about 125 million
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housing units exist in the United States. That means porch lights could consume a total of 22 billion kWh. The amount of greenhouse gases emitted per kWh of electrical energy produced depends on the production method. The coefficient is about 2 pounds of carbon dioxide per kWh if electricity is derived from the combustion of coal, which currently fuels nearly half of U.S. electricity generation. The burning of other fossil fuels, mostly natural gas, generates almost a quarter of our electric energy needs. About another one-fifth comes from nuclear power. The remainder comes from renewables, including wind, solar, and geothermal energy. The U.S. Environmental Protection Agency has a greenhouse gas equivalencies calculator at its Web site (www.epa.gov/cleanenergy/ energy-resources/calculator.html). Based on the current mixture of electricity-generation methods, about 1.6 pounds of carbon dioxide equivalents are produced per kWh generated. Therefore, saving 22 billion kWh of electricity would reduce greenhouse gas emissions by 16 million metric tons. This is 0.03 percent of the approximately 50 billion tons of annual worldwide greenhouse gas emissions from human activities.
The big chill Is there a chance that there will be another ice age?
Because large ice sheets still exist in Greenland and Antarctica, we technically still live in the ice age that began millions of years ago. By a more colloquial definition, the last ice age, or period of extensive advance of ice sheets toward the equator, ended 10,000 years ago. Climatologists refer to these colder periods within an ice age as glacial periods and the warmer periods (like the present) as interglacials. Not long ago, many climatologists were predicting that Earth was headed into a glacial period. What appeared to be a warming trend in the early part of the twentieth century, after the “Little Ice Age,” shifted to cooling from 1940 to the late 1960s. (Your relatives in the Midwest or eastern U.S. or Europe weren’t exaggerating—winter really was snowier back in the good old days.)
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Until the warming trend resumed in the 1970s, much disagreement swirled over whether the world had entered into a long-term cool spell. The cooling turned out to be temporary and localized to the Northern Hemisphere. Particulate matter in the atmosphere from industrial pollution (most prevalent in the Northern Hemisphere) may have played a role by reflecting incoming solar radiation. New regulations and pollution-control technologies had started to clear the air around the time the warming resumed. Glacial periods happen on a quasiregular basis, so we should eventually plunge into another. However, computer simulations suggest that the increasing levels of carbon dioxide in the atmosphere may lock Earth into an irreversible greenhouse effect and stave off future ice ages. That sounds terrific (especially to weather wimps like me), but the climate system may have some tricks in store. For example, the sinking of dense, salty water in the North Atlantic helps drive a conveyer belt of currents around the globe that ultimately brings warm water back to the North Atlantic. Some researchers are worried that fresh water from the melting of glaciers could create a “lid” that reduces the sinking that helps drive the globe-girdling current. Most researchers do not think the current would shut down completely, but reductions in flow could chill Europe and have wide-ranging effects on climate elsewhere.
The little chill I’ve recently seen a few programs about the “Little Ice Age,” yet they were all about the Northern Hemisphere. What was happening in the Southern Hemisphere at that time? The term “Little Ice Age” has been used to describe a cool period between roughly the seventeenth and nineteenth centuries. No consensus has arisen on when the Little Ice Age began and ended. Some scientists place the beginning as early as 1300, when the ice pack around Greenland began to grow. The most detailed climate information about the Little Ice Age comes from Europe and North America. Evidence also shows that mountain glaciers advanced during this period in a number of regions Download at www.wowebook.com
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in the Southern Hemisphere, including New Zealand, Chile, and Peru. Glaciers advanced and retreated throughout the Little Ice Age in a zigzag of climactic shifts instead of simply advancing continuously. The cause of the Little Ice Age is not well understood. Historical records reveal that there was a remarkable lack of sunspots at the height of the Little Ice Age. Scientists think this could mean that changes in solar activity played a role. Volcanic activity probably also contributed to the cooling. In the 1600s, the world experienced at least six climactically significant volcanic eruptions. Several major eruptions also took place in the 1800s, including Mt. Tambora in Indonesia in 1815, which may have been the largest eruption in the last 15,000 years. Large volcanic eruptions produce cold episodes because ash particles sent high into the stratosphere block solar radiation. Even within the Northern Hemisphere, the average temperature during the Little Ice Age was less than 1°C cooler (about 34°F) relative to late-twentieth-century temperatures. Cooling was considerably more pronounced in some areas, suggesting that regional climate changes may have been largely independent. Complex interactions between the atmosphere and the ocean affect regional climate. Sea surface temperature anomalies, such as the North Atlantic Oscillation (NAO) and El Niño in the central tropical Pacific Ocean, alter the movement of air masses and, therefore, alter temperature and moisture distributions. Century-scale changes in the NAO may have chilled Europe during the Little Ice Age. When the NAO changes phase and winds blow from the northeast, Europe is bathed in cold air from Siberia rather than heat from the Atlantic’s surface. Similarly, in some parts of South America, glacial advances during the Little Ice Age have been tied to periods of few El Niño events.
Capricious cycles In the global warming debate, why are Earth’s cycles of warming and cooling never talked about? As recently as 30 years ago, we humans were scared of global cooling. Now it is global warming. What if Earth is moving into another cycle?
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During the most recent geological era, glacial/interglacial cycles have occurred every 100,000 years, on average. Scientists have proposed more than 30 different models for these cycles, most of which attribute the timing of glaciations to regular, slow changes in three factors: Earth’s orbit around the sun, the tilt of Earth on its axis, and the orientation of its axis. Other models attribute the cycles to random internal climate variability. Statistical tests of the models suggest that Earth’s tilt is the dominant factor controlling glacial cycles. Earth’s tilt changes from 22° to 24.5° every 41,000 years. Glaciations end when the average annual sunlight reaching high latitudes increases, which occurs as the tilt of Earth’s axis increases. It may take two or three 41,000-year tilt phases for the ice sheets to grow large enough to become sensitive to changes in Earth’s tilt. Feedback within Earth’s climate is important: The bigger the ice sheets get, the more sunlight they reflect and the more Earth cools. The tilt of Earth is currently 23.5° and decreasing. Therefore, Earth should slowly be moving toward a period in which the ice sheets advance. Of course, other natural factors affect climate within each glacial or interglacial period, including volcanic activity and solar activity. Variation in solar activity is favored as an alternative explanation for global warming by individuals who dispute the role of humanproduced greenhouse gases. But recent research shows that although solar cycles might explain the warming in the first half of the last century, it cannot explain the change in global temperatures over the past two decades. During that time, the sun’s output declined. Today more certainty surrounds global warming than was the case in the 1970s with global cooling, because vastly more research exists on how and why climate changes. Still, the effects on future climate of natural sources of variability, such as solar activity and volcanic activity, are currently unpredictable.
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For good measure Articles about climate change often report average regional and global temperatures to the hundredth of a degree. How are temperatures for Earth and specific regions determined now, and how were they determined in the recent past? How certain are average temperature measurements? The instrumental period—the era of regular global thermometerbased temperature measurements—began in the 1850s. Accuracy has improved gradually over the instrumental period, with the geographical expansion of coverage and the introduction of new methods of data collection and averaging. Current global temperature datasets are derived from measurements taken at more than 4,000 stations on land, as well as seasurface temperatures recorded by ships and buoys. Satellite microwave and infrared imagery has supplemented marine temperature measurements since about 1980, and it is now possible to monitor land surface temperature with satellites. Nonclimatic factors influence long-term temperature data. Random influences include changes in station location or instruments. Systematic changes can occur due to the introduction of new algorithms to calculate daily or monthly mean temperatures. When the cause of an observed discontinuity in temperature data at a site is not known, comparisons with neighboring sites can factor out nonclimatic influences. Other adjustments may be needed, for example, to assess seasurface temperature measurements taken by different methods. Before the 1940s, sea water was usually collected in uninsulated buckets for temperature measurements. Now temperature is often measured at ships’ engine inlets or hull sensors. Also, a calibration procedure relates the ocean “skin” temperature measured by satellites to ship and buoy temperature data, which are collected in the upper few meters of the ocean.
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Temperature datasets do not have uniform coverage across the globe. Land-based measurements are sparsest over the interior of Africa, South America, and Antarctica. Measurements of sea surface temperature are densest along main shipping lanes and sparsest in the Southern Ocean. Computational modeling is required to average temperature data across large regions and blend land and marine data. The models share some of the same raw data, but the averaging methods and the treatment of gaps in the data differ. Although the data combination methods differ among models, they reveal similar warming trends. Each model provides a global temperature trend per decade estimated to be accurate within 0.05°C (0.09°F), which is also the maximum variation among the major models used (from NASA; the Hadley Center; Remote Sensing Systems; and the University of Alabama, Huntsville). Therefore, the global decadal warming trends are not certain beyond two decimal places. They may be recorded with three decimal places to permit calculations to be made without additional rounding error.
The case of the missing oxygen Given the quantity of fossil fuel being burned, one would expect a measurable consumption of atmospheric oxygen where the emissions are carbon dioxide and water vapor. Is this due to occur eventually? Only within the past two decades has it become possible to measure the small changes in oxygen concentration due to the burning of fossil fuels. These measurements are technically difficult because the background concentration of oxygen in the atmosphere is so large. Oxygen makes up nearly 21 percent of the atmosphere, a concentration more than 500 times greater than that of carbon dioxide. The very sensitive measurements show that the burning of fossil fuels is consuming atmospheric oxygen (see Nature, August 27,
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1992). The decline is about a ten-thousandth of 1 percent of the total amount of oxygen in the atmosphere.
Under pressure Barometer readings that measure atmospheric pressure are not changing. Where are the cumulative emissions of millions of tons of greenhouse gases? The combustion of fossil fuels yields carbon dioxide (CO2) and water vapor (H2O). The atmospheric concentrations of both gases are increasing. But because the oxygen atoms in both gases come from atmospheric oxygen (O2), only a portion of the emissions (the carbon and hydrogen from fossil fuels) is “new” mass being added to the atmosphere. The mass of the atmosphere would increase by the mass of fossil fuels burned if the chemical equation for combustion were the sole factor to consider. The other critical factor is that only about twothirds of the carbon dioxide released by the burning of fossil fuels remains in the atmosphere. The oceans absorb the remaining carbon dioxide, which reacts with water to form carbonic acid. Accounting for the uptake of carbon dioxide by the ocean, the mass of carbon dioxide and water vapor being produced is roughly equal to the mass of oxygen being consumed. Although these calculations are not precise because the burning of fossil fuels also involves other chemical reactions, any pressure changes caused by the burning of fossil fuels are small compared to normal fluctuations in atmospheric pressure. On the other hand, global climate change has had measurable effects on the density of different layers of the atmosphere. As Earth’s surface has warmed by a fraction of a degree, at higher altitudes (30–50 miles), the atmosphere has cooled by several degrees and contracted (see Science, November 24, 2006). Because this pulls the intervening layers downward, the density of the atmosphere where satellites orbit (above 100 miles) has declined. With less drag, satellites will stay aloft longer, but so will potentially damaging spacecraft debris.
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Nature burps? I read an article that said nature generates about 30 times as much CO2 as man does. Just what is the role of anthropogenic CO2 in the great debate? The climate change issue has plenty of legitimate scientific debates, such as the extent of future warming and sea level rise, the role of future solar activity and volcanic activity, the best ways to model the effects of atmospheric particles—which, depending on their identity and location, can lead to warming, cooling, or cloud formation (itself challenging to model)—and the influence of oceanatmospheric circulation patterns. However, whether the increase in atmospheric carbon dioxide is less than, equal to, or greater than what humans have produced is measurable and, thus, should not be a source of controversy. Just as a sustained increase in calorie intake (with no other changes) results in a slowly expanding girth, the billions of tons of anthropogenic (human produced) carbon dioxide emitted annually should be expected to accumulate in the environment. Indeed, the concentration of carbon dioxide in the atmosphere has increased since the industrial revolution from 280 parts per million (ppm) to nearly 390 ppm. The increase in atmospheric carbon dioxide is two-thirds or less of what humans have produced from burning fossil fuels and manufacturing cement during that period. Counting estimated effects of deforestation and other land use changes, the increase in atmospheric carbon dioxide is around half of what humans have produced. In other words, the article is dead wrong on the relative amounts of carbon dioxide produced by humans and nature. Nature is acting as a net absorber of carbon dioxide rather than a net producer. (So as not to be guilty of countering one unsupported assertion with another, an article in the July 16, 2004, issue of Science details nature’s role as a carbon dioxide sink.) Carbon dioxide is the second-most-important greenhouse gas, after water vapor, causing around 20–30 percent of the greenhouse
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effect. (That figure comes from the February 1997 issue of the Bulletin of the American Meteorological Society.) Increasing atmospheric carbon dioxide concentrations are having another significant, measurable environmental impact: ocean acidification. The oceans have absorbed much of the “missing” carbon dioxide, the anthropogenic carbon dioxide that has not remained in the atmosphere. Carbon dioxide dissolves to form carbonic acid, which is corrosive to coral and other creatures with calcium carbonate shells. Many of these organisms are at the base of food chains, so acidification could have profound effects on ocean ecology.
Cause or effect? Some say carbon dioxide is a result of rising temperature, not an effect. Care to respond?
Rising temperature is both a cause and a result of increasing atmospheric carbon dioxide. Scientists think that at the end of the ice ages, changes in Earth’s orbit led to the initial warming, which caused carbon dioxide to be released from the oceans. The increased carbon dioxide in the atmosphere resulted in additional warming, which stimulated more carbon dioxide release, and so on. On one hand, carbon dioxide causes warming by holding back infrared rays radiating from Earth, reducing the amount of thermal energy that escapes into space. On the other hand, warming causes an increase of carbon dioxide in the atmosphere because, as it does in a glass of soda, carbon dioxide becomes less soluble in sea water as water temperature increases. The ocean is currently a significant sink for carbon dioxide. Future estimates of carbon dioxide uptake by the oceans must account for the effect of the predicted temperature increase on the ability of carbon dioxide to dissolve in sea water. One way scientists can trace the carbon dioxide increases to human activities is by using isotopes, or types, of carbon. Release of carbon dioxide from sea water should not significantly change the ratio of carbon-12 relative to carbon-13 isotopes in the atmosphere.
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Yet the amount of carbon-12 relative to carbon-13 in the atmosphere has increased since the industrial revolution. Because plants, from which fossil fuels are derived, preferentially incorporate lighter carbon-12, the carbon isotope “fingerprint” is consistent with fossil fuel burning as the source of much of the increased carbon dioxide.
Back to the drawing board Nuclear power generates approximately 20 percent of U.S. electricity needs. Recently, the U.S. Secretary of Energy curtailed development of Yucca Mountain for long-term handling of nuclear waste. What is the current U.S. policy for nuclear waste by-products? Is the current policy adequate to protect the public? Plans for a geologic repository for spent nuclear fuel at Yucca Mountain in Nevada have been shelved, yet concerns about energy independence and global warming have rekindled calls to increase nuclear power generation. The United States does not currently have a backup potential long-term repository. In 1987, the U.S. Congress selected Yucca Mountain as the only site to be investigated for a permanent nuclear waste storage facility. The Department of Energy (DOE) spent more than $13 billion researching the site. The final projected cost of developing the repository topped $75 billion, not including the cost of transporting the 60,000 tons of existing waste from reactor sites. The DOE initially set out to design a facility that would be safe for at least 10,000 years. A recent ruling forced the DOE to extend the safety guarantee to one million years because the half-lives of some elements in the spent fuel are hundreds of thousands of years. While the DOE goes back to the drawing board, the waste will remain at nuclear plants around the country. There, after spent fuel rods are removed from a nuclear reactor, they are placed in steellined concrete pools to cool. A few years later, they are removed, dried, and sealed into steel containers, which are packed into concrete silos. This is considered a safe medium-term storage option.
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At the beginning of the nuclear age, the United States planned to reprocess spent nuclear fuel, because the dominant type of nuclear reactor (the light-water reactor) consumes only a tiny percentage of the fissionable material before the reaction halts. U.S. reprocessing ceased after India’s 1974 nuclear test, which used plutonium separated with U.S. aid for civilian purposes. Economics, rather than nuclear proliferation risk, is now the main reason reprocessing is out of favor, even in a number of countries that had been reprocessing spent fuel. The cost of natural uranium has declined since large deposits were discovered in Canada and elsewhere. Thus, it is cheaper to make new fuel rods (albeit, ignoring disposal costs). New fast reactors that can process spent fuel rods could provide a technological solution, but they are much more expensive to build and run than conventional reactors. For now, the unwanted rods remain in steel-and-concrete limbo.
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6 Home planet Continents set sail Will another ocean ever be formed? Earth got another ocean in spring 2000. In case you are wondering how you missed the cataclysmic planetary event, it was not quite that dramatic. The International Hydrographic Organization (IHO) decided to demarcate the Southern Ocean, the world’s fifth ocean, in addition to the Pacific, Atlantic, Indian, and Arctic Oceans. The Southern Ocean extends from 60° south latitude to the coast of Antarctica. Just as new scientific data led pesky astronomers to demote Pluto to dwarf planet status, new data led the IHO to create the Southern Ocean. Recent interest in global climate change has stimulated research on ocean circulation. One of the findings is that a huge, globe-girdling current in the Southern Ocean separates it into a distinct ecosystem. So although all the world’s oceans are joined, the IHO decided sufficient evidence existed to consider the Southern Ocean a discrete entity. Besides research leading to new labels on the globe, real planetary changes do alter the distribution of blue. It has happened many times in our planet’s past. Ancient oceans were joined and split as the continents changed their configurations. If the continents look as if they would fit together as pieces of a jigsaw puzzle, it is because they were previously joined together in a landmass known as Pangaea. A young German scientist, Alfred
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Wegener, proposed this in 1912 to explain the similarities in rock formations, fossils, and living things on the different continents, and to explain why climates were distributed differently in the past. At the time, the scientific community met Wegener’s ideas with considerable skepticism. By the 1960s, studies of the ocean floor led to a revolution in scientific thinking. Today it is well accepted that Earth’s crust consists of plates that move approximately an inch or two per year. Plate tectonics, as the theory is known, explains earthquakes, volcanoes, and mountain building. Plate tectonics also explains how, during the course of 200 million years, the vast Atlantic Ocean grew between the Americas and Europe and Africa, and continues to grow today. At the center of the Atlantic Ocean is a long chain of volcanoes. As lava rises, the solidified lava alongside it that was produced in previous eruptions moves outward, and the ocean floor behaves as a conveyor belt. Meanwhile, the Pacific is shrinking as portions of the Earth’s crust beneath it are forced downward in deep trenches. The heat within the Earth drives these motions. Therefore, the shapes, sizes, and locations of the ocean basins are constantly changing. It is likely that new oceans will form as the continents shift, but when and where depends on how Earth’s plates redistribute themselves during the next tens of millions of years. One possibility is the Afar region of Ethiopia, where a giant crack opened along a rift in Earth’s crust in 2005. This has led researchers studying the area to predict that as the African and Arabian plates continue to drift apart, Africa will split along the rift and a new ocean will form between the eastern and western parts of the continent.
The abyss Where is the deepest part of the ocean, and how deep is it? It is the Mariana Trench in the Pacific Ocean, just east of the Mariana Islands near Japan. The trench was created by one oceanic plate slipping beneath another. It is 36,000 feet deep—deep enough to swallow Mount Everest with more than a mile to spare.
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Tiny tides We have high and low tides in the seas and oceans of the world, but why don’t we have high and low tides in the Great Lakes, such as Lake Michigan and Lake Superior? The Great Lakes actually do have tides. According to Newton’s law of gravity, the force of gravitational attraction between two bodies varies with the product of the masses of the two bodies. So the gravitational attraction between the moon and an ocean is a lot bigger than between the moon and a lake. The tides in the Great Lakes are less than 2 inches in height according to the National Oceanic and Atmospheric Administration. Therefore, changes in wind and barometric pressure tend to mask the tides. Weather conditions can lead to tidelike changes in water levels in lakes. For example, strong winds blowing from one direction can push the water level up on one side of a lake, causing a corresponding drop on the other side. When the wind subsides, the water sloshes back and forth similar to water in a bathtub, rising on one side of the lake and dropping on the other, and then reversing. From the shore, this slow oscillation—known as a seiche—resembles a tide.
Raisin planet When the pressure inside a balloon is slowly diminished, the surface of the balloon begins to shrivel. As our civilization extracts oil, gas, and other minerals from the interior of Earth and volcanoes emit lava and gases, could the surface of Earth become deformed, causing earthquakes and warming of the ocean? Even though the deepest mines extend less than 2 miles into the ground and the deepest drill holes reach only about 8 miles, the exploitation of our planet’s resources considerably alters its surface. The most significant change is subsidence—the decrease in elevation of the land surface resulting from the removal of water, oil, and gas, and the collapse of underground mines.
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Subsidence is a worldwide problem. It damages roads, buildings, canals, levees, and other structures. It has also led to flooding in coastal areas that were originally above high-tide levels. Not all the subsidence land movement is vertical. Horizontal shifts lead to breaks in the surface, which can erode to form large fissures. More than 80 percent of the subsidence in the United States results from the removal of ground water, according to a report by the U.S. Geological Survey. For example, some areas of California’s San Joaquin Valley have dropped 30 feet in 75 years. In aquifers containing layers of silt and clay, reduced water pressure can cause permanent compaction of soils and loss of water storage capacity. Geologists have shown that natural or artificial changes in groundwater, tides, snow load, or other alterations of stress on a fault can cause earthquakes. (Perhaps such changes can also suppress earthquakes, but that would be difficult to show.) Large earthquakes can sometimes trigger eruptions in volcanoes up to about 500 miles away. Overall, the number of earthquakes and volcanic eruptions does not appear to be increasing. A link between land subsidence and ocean temperatures also appears unlikely. Volcanic activity alters the landscape locally, but it does not shrink Earth’s surface. The belching of volcanoes is quite different than the release of air from a balloon. As magma works its way toward the surface, the pressure on it drops. Consequently, the rapid expansion of water in magma to form a gas can propel molten rock into the air. The center of Earth is not suffering a net loss of material because rock and water return to the depths at subduction zones, places where regions of the Earth’s crust plunge beneath one another. The heat that brings magma to the surface is also continually being generated by the decay of radioactive elements deep within Earth.
Volcanic variety show Why do some volcanoes, such as Mount St. Helens, explode violently, but others, such as currently active volcanoes in Hawaii, behave less destructively?
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Volcanoes display a multiplicity of eruption styles. The explosiveness of a volcanic eruption depends on the chemical composition of its magma, the magma’s viscosity, and the rate at which it rises to the surface. Types of volcanic eruptions are typically named after well-known volcanoes with characteristic behaviors, although during a period of activity, a volcano may go through a sequence of eruption types. The most violent eruptions that blast ash high into the atmosphere, such as the 1980 eruption of Mount St. Helens, Washington, and the 1991 eruption of Mount Pinatubo, the Philippines, are called “Plinian.” Plinian eruptions and other explosive eruptions—including Pelean, in which avalanches of hot gas, ash, lava, and rock rush downslope; and Vulcanian, characterized by large clouds of gas and ash—are produced from viscous magma that is high in dissolved gases, especially water vapor. At the other end of the violence scale are Strombolian eruptions, with their intermittent blasts of lava clots, and Hawaiian lava fountains, produced from runnier magma that is lower in dissolved gases. Dissolved gases in magma influence a volcano’s explosiveness because the magma decompresses as it ascends from within Earth. The dissolved gases form bubbles, behaving similar to the way soda does when the lid is removed from the bottle. Viscosity of magma influences explosiveness because bubbles can less readily escape from magma that is thick and syrupy. The magma’s speed of ascent determines the rate at which the external pressure on the magma decreases. When decompression causes the bubbles to expand faster than the liquid films surrounding them can spread, the films rupture and a hot mixture of ash and gases ascends to the volcanic vent. A volcano’s location plays a role in how explosive it is because the composition of magma changes as it interacts with overlying rocks. Most volcanoes are associated with the boundaries between shifting plates in Earth’s crust. The periphery of the Pacific Ocean marks the boundary of several plates, and this highly volcanically active region has earned the moniker “Ring of Fire.” Rocks in plates being pushed beneath one another are often high in water-rich minerals. They produce magma with high water content.
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In contrast, the Hawaiian Islands are not on a plate boundary. Their activity is attributed to thermal plumes, or “hotspots.” There, upwelling magma does not interact with water-rich rocks. Thanks to the low water content of the magma, Hawaiian volcanoes tend to be relatively gentle giants.
Serpentine smoldering What portion of our current global warming is caused by the more than 200 million tons of coal that goes up in flames in the coal mines of China and India each year, and what can the United States do to motivate these countries to develop the technology to extinguish them and prevent these fires from occurring? Thousands, possibly even hundreds of thousands, of coal fires are burning around the world. The problem is most severe in China, where scientists estimate that between 20 million tons and 200 million tons of coal burns each year, producing up to 1 percent as much carbon dioxide as global annual human-induced emissions. It is difficult to assess exactly how much coal is burning because the fires extend deep underground. Coal fires have a long history. Marco Polo mentioned them in his travel documents on China as “the burning mountains along the silk road.” Many land formations across the American West are made of reddish pyrometamorphic rock—rock baked by ancient coal fires— that was left behind when softer, unbaked rock eroded. Coal can ignite spontaneously when exposed to air, if the heat that is slowly produced by the reaction of coal and oxygen cannot escape to the surroundings. Another natural cause of coal fires is lightning strikes. Human activities have made coal fires more prevalent. Forest fires, slash-and-burn agriculture, and burning garbage can ignite coal seams that are close to the surface. Mining increases the risk of fire by exposing coal to oxygen. Satellite imaging is improving the detection and mapping of coal fires. Signs of coal fires include heated ground, cracks and fissures venting hot gases, degraded vegetation, pyrometamorphic rocks, and
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fumarolic minerals—minerals that are dissociated from rocks by the heat of the fires and transferred along cracks to the surface where they recrystallize. Sealing entrances and ventilation systems in old mines and avoiding surface fires that can ignite the coal beneath can help prevent coal fires. Small coal fires can be fought by digging trenches to isolate the fire and by sealing fissures with soil to cut off the oxygen supply. Pumping water rarely works because the mines are too large and the surrounding rock is too fractured. Some efforts in China and elsewhere aim to extinguish coal fires, but the problem is overwhelming. In Pennsylvania, the entire town of Centralia was condemned after initial attempts failed to extinguish coal fires started in the 1960s by burning garbage. It was deemed cheaper to relocate the residents than to fight the fires, which are still burning today.
From swamp to SUV Why are fossil fuels found at such depths below the surface of Mother Earth? Crude oil formed from microscopic plants and animals that lived in ancient seas. Coal formed from trees, ferns, and mosses that grew in swamps and bogs. When these organisms died, they settled on the seafloor or bottom of the swamps. Over millions of years, they were buried under layers of silt and sand, and chemically transformed by the resulting heat and pressure. The accumulation of fossil fuels from biological organisms occurs in the outer layer, the crust, of Earth. Some scientists think that oil is also produced when rocks that contain carbon are subjected to high pressure deep within Earth, in its mantle. This abiogenic—from nonbiological origins—theory of oil formation is controversial. Abiogenic processes can produce oil, but geologists disagree over whether they produce commercially useful quantities.
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No smoking crater? In a recent “Science Brief,” the Chicxulub impact event was summarily dismissed as an explanation for the demise of the dinosaurs at the Cretaceous–Tertiary (K–T) boundary. The timing was off by 300,000 years. How can researchers be so wrong? It is difficult to determine the age of the Chicxulub crater definitively because the layers of sediment have been disturbed, according to Mark Thiemens, dean of the University of California, San Diego’s Division of Physical Sciences, who studies past climates and events using isotope measurements. Since it was created, the Chicxulub crater has been covered by about a half-mile of sediment. To determine which layer of sediment represents the bottom of the crater, researchers look for the presence of tiny glass beads. These beads are produced when a powerful impact liquefies and ejects rock, which cools and solidifies in flight. The age of the sediment layer that contains the glass beads should be the age of the crater. However, the beads tend to settle over time. Thiemens says this is especially problematic for a crater in the sea, where the burrowing of marine worms disturbs the beads. Because the lower layers of sediment are progressively older, sinking of the beads would lead to an overestimation of the crater’s age, which may explain why the Chicxulub impact appears to be 300,000 years older than previously thought. (It is difficult to date the beads themselves.) Although the exact age of the crater is uncertain, Thiemens points out that little dispute exists about the age of the famous K–T boundary. The discovery that the K–T boundary—a layer of rock around the world that is 65 million years old—contains a high concentration of iridium led to the hypothesis that a collision with a large asteroid wiped out the dinosaurs. Iridium is not abundant in Earth’s crust, but it is abundant in asteroids. This finding provides good evidence for an asteroid impact 65 million years ago. It was probably Chicxulub, but we cannot rule out that another impact around the same time produced the K–T boundary.
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Still, controversy remains about whether an impact led to the dinosaurs’ demise. The fossil record suggests that dinosaur diversity started to decrease several hundred thousand years before the impact. During this period, two relevant geological changes were occurring. Shallow seas that had covered vast areas of the continents were receding as the continents slowly changed position. Intense volcanic eruptions were producing the Deccan Traps in India. Receding seas, volcanic ash, and fallout from an impact and subsequent fires would alter climate. Any or all of these events could have played a role in the extinction of the dinosaurs.
Superseded scale Quakes are measured in “magnitude and a number.” Why do some articles still refer to the Richter scale? Geologists have stopped using “Richter scale” in scientific literature. But the term persists in the media because the public has an intuitive understanding of it. Journalists should stop using the term so geologists would no longer be asked where to buy a Richter scale— which is a mathematical formula instead of a piece of equipment. Charles Richter developed his scale in 1935 to calculate the magnitude of moderate earthquakes in southern California from recordings on local seismographs. The newer methods of measuring earthquake magnitudes were developed because Richter’s methods do not yield accurate magnitudes for very large (magnitude greater than 7) quakes, quakes recorded more than 400 miles from their epicenter, or quakes in very deep rock. Fortunately, most of the new methods are designed to be consistent with the Richter scale. The United States Geological Survey now uses “moment magnitude,” “magnitude,” or simply “M.” These magnitude numbers may be calculated differently than Richter’s, but your intuitive understanding of the numbers—such as a magnitude 5 versus 6—still applies. (The 6 quake is approximately 30 times more energetic than a 5 quake.) In terms of comparing how much damage an earthquake does, all the magnitude scales are inadequate because they are concerned only Download at www.wowebook.com
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with how much energy an earthquake releases. Amount of damage caused depends on several additional factors, including distance from the epicenter and the type of underlying rock or soil. The Modified Mercalli Intensity Scale is the best measure of the destructiveness of an earthquake. It is a 12-level ranking of observed effects, from “not felt” to “all structures destroyed.”
Doin’ the wave At what speed from the epicenter does the wave of an earthquake travel? The rupture of a fault creates four main types of waves: primary, secondary, Love, and Rayleigh waves, which travel at different speeds. Primary waves, or P waves, alternatively push and pull at the material they are traveling through, similar to a Slinky being stretched and compressed. P waves are the fastest, with speeds of 1 to 14 kilometers per second (km/s), or 2,250 to 31,500 miles per hour. The speed of the waves varies according to the material they are traveling through—speed is greater through solid rock than looser soil or liquid and increases with depth (and pressure) into the Earth. Secondary waves, or S waves, shear the rock sideways at right angles to the direction of travel. Their speed is 1 to 8 km/s depending on the material, and they travel only through solids. Although the speed of the P and S waves vary, the ratio between their speeds remains relatively constant and can be used to calculate the distance to the earthquake’s epicenter. P and S waves travel below the surface of Earth, whereas Love and Rayleigh waves are surface waves and do the most damage. Love waves move the ground from side to side with no vertical displacement. Rayleigh waves move the ground horizontally and vertically. Both types of surface waves are slightly slower than S and P waves, with Rayleigh waves being the slowest (around 1–5 km/s). The P waves are often too small to be felt by humans, but some animals can sense the vibrations or hear these waves. This is why dogs barking may seem to predict the earthquake. The earthquake has
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already occurred, but humans find out about it only when we feel the more forceful shaking of the later-arriving waves.
Shake, rattle, and roll I met a very educated young man who said that he had heard that Earth had tilted 4° off its axis because of the volume of water that was moved around the globe during the 2004 Asian tsunami. Is this true? If so, what could be some of the effects of this? The shift in mass caused by the earthquake and tsunami did make Earth wobble on its axis. It also decreased day length. (“Aha,” you say, “that’s why I feel so busy lately!”) According to calculations by geophysicists at NASA’s Jet Propulsion Laboratory, the earthquake slightly reduced the bulge at the equator. Similar to a skater pulling one’s arms closer to the body, this caused Earth to spin faster. These effects are much smaller than your acquaintance suggested. Even though the December 26, 2004, earthquake had a magnitude greater than 9, the amount of mass redistributed was tiny compared to the total mass of the planet. The NASA geophysicists’ calculations revealed that the Earth tilted about an inch (2.5 centimeters) on its axis and that the day length decreased by 2.7 millionths of a second. The earthquake-induced wobble and change in day length are insignificant relative to normal variations in each. Both can be affected by forces that redistribute mass on Earth, including weather systems such as El Niño and La Niña, which alter the distribution of the wet and dry areas of the world. Also, Earth does not rotate perfectly around its axis; about every 14 months, the axis wanders in a circle about 40 feet (12 meters) in diameter. Other than the wobbling a tiny fraction of a degree, the tilt of Earth remains pretty stable from year to year, 23.5° relative to the plane of Earth’s orbit around the sun. The tilt is the reason we have seasons. When the Northern Hemisphere is oriented away from the sun, the sun’s rays strike the ground there more obliquely. With less sunlight, it is winter in the North. By summer, Earth has revolved
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halfway around the sun; hence, the Northern Hemisphere is oriented toward the sun. Over the longer term, in cycles of approximately 41,000 years, Earth’s tilt changes from about 22° to 24.5°. These tilt cycles are one of the factors responsible for ice ages. When the tilt is smaller, summers are cooler and ice is more likely to last from year to year. Therefore, had the earthquake tilted Earth by 4°, it could have had a significant effect on global climate.
Pugilistic plates Is there a relationship among the January 12, 2010 earthquake in Haiti, the preceding volcanic eruption in Costa Rica, and the earthquake in Guatemala? Do scientists expect to see increased activity in the plates abutting the Caribbean plate? The movement of the Caribbean plate is the result of dynamic interactions with the neighboring hunks of Earth’s crust, the North American, South American, Cocos, and Nazca plates. The magnitude-7 Port-au-Prince earthquake occurred on the Enriquillo–Plantain Garden Fault—one of a network of faults that runs along the contact zone between the Caribbean and North American plates, a boundary that is delineated by the arc of islands that form the Greater Antilles and Lesser Antilles. The Caribbean plate slips eastward 20 millimeters per year relative to the North American plate, but the Enriquillo–Plantain Garden Fault has been relatively quiescent for a century or more. Because it was stuck, the fault was identified as a seismic hazard. Future increased activity along the Enriquillo–Plantain Garden Fault is expected because large events create new stresses that slowly work their way out. These aftershocks may be scattered along the fault or may follow a pattern, as with the several large earthquakes that seem to have propagated from east to west along the fault beginning in 1751. Earthquakes can sometimes have long-range effects. For example, the 2002 magnitude-7.9 earthquake in Denali, Alaska, triggered
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small earthquakes 2,000 miles away in Yellowstone National Park and changed the activity of Yellowstone’s geysers. However, the apparent pairing of earth-shaking events is usually coincidence because of the sheer number of events that occur. The U.S. Geological Survey publishes the locations for about 40 earthquakes per day, but its researchers estimate that millions of earthquakes occur annually. About 50–70 volcanoes erupt each year, 20 or so at any given moment, not including the many undersea volcanoes. The world’s most seismically active region—the horseshoeshaped Ring of Fire that encircles the Pacific Ocean—is the site of the volcanic eruption in Costa Rica and the earthquake in Guatemala. Although in the short term such events are not likely to be linked, over the long term, earthquakes on different plates may be related. Studies of the patterns of earthquakes that have occurred around the world during the past century suggest that stress in Earth’s crust that results from a series of large earthquakes in one region can transfer along the boundaries between adjacent plates.
Redrawing the map If an earthquake on the San Andreas Fault shifted the land 5 meters northward at the San Diego–Tijuana border, what would be done with the physical objects at the surface? Would the United States own the land that was previously on the Mexican side? If the border fence and all the objects along the border shifted in unison, the U.S.–Mexico border would simply be 5 meters farther north. If the land shifted unevenly, negotiations between the two countries would probably be necessary to define the new border. Geological changes can affect borders. The Pacific Plate is moving northwest 2 to 3 inches per year, shifting the U.S.–Mexico border. In addition, geomorphological changes—alterations in the features of Earth’s surface through processes such as erosion—can occur even more quickly. Many borders are drawn along rivers, which can alter their course significantly over time.
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Many border disputes exist around the world, but none stems from geological or geomorphological changes, according to Yehuda Bock, a Scripps Institution of Oceanography geodesist—someone who studies the shape of Earth and how its surface deforms over time, providing the mathematical underpinning for mapmaking. This may seem surprising, but Bock points out that maps vary depending on which reference system is used to draw them. Differences between maps dwarf the changes in Earth’s surface caused by earthquakes and erosion. Most maps of the United States are currently based on either the North American datum 1927 or the North American datum 1983. A datum is a mathematical model of the shape of Earth, and a reference point on Earth’s surface used to make measurements and assign coordinates. Switching datums can change the assignment of a point on Earth’s surface by hundreds of feet. Uncertainty about the particular datum used to generate a historical map and the possibility of survey blunders can complicate the resolution of border disputes. The drawing of highly accurate maps based on global positioning system (GPS) data is still in relatively early stages. Bock is also the director of the California Spatial Reference Center (CSRC), which has the mission of determining how any point in California is moving over time. Researchers at the CSRC are collecting information in real time from hundreds of GPS stations all over the state. They are using mathematical modeling to describe how Earth’s crust shifts because of earthquakes and subsides due to the extraction of water and oil. The CSRC’s work will be useful in addressing any border or boundary disputes that may arise from earthquakes or other geophysical processes.
Slip slidin’ away Is it really possible that a portion of California will break off or sink into the ocean someday? If so, would it be noticeable that it was happening?
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Fortunately for Californians, and unfortunately for Nevadans and Arizonians hoping for beachfront property, the Golden State is not in danger of dropping into the ocean. However, the Pacific Plate is sliding past the North American Plate at the rate of 2 inches per year along the San Andreas Fault system—which extends from Cape Mendocino in northern California to the Salton Sea in southern California—and other geologically complex faults extending into Baja. In around 15 million years, something strange will happen: Los Angeles and San Francisco will become neighbors.
Hot date How can we trust carbon dating when so many factors, such as the ice age and other environmental factors, greatly interfere? Carbon dating involves quantifying radioactive carbon-14. Carbon-14 and carbon-12 (the most abundant form, or isotope, of carbon) are both present in the atmosphere and become incorporated into plants when plants use carbon dioxide to make sugars. Animals eat plants, or eat animals that eat plants; therefore, living plants and animals contain a ratio of carbon-14 to carbon-12 that reflects the ratio of these isotopes in the atmosphere. After an organism dies and stops taking in carbon, the ratio of carbon-14 to carbon-12 declines because carbon-14 undergoes radioactive decay, but carbon-12 is stable. Therefore, the quantity of radioactive carbon relative to stable carbon reveals the age of an artifact of plant or animal origin. How much carbon-14 is present in an artifact depends on how fast carbon-14 decays and how much carbon-14 was initially present. Each radioactive isotope has its own characteristic rate of decay that depends on forces in the nucleus of the atom, not on environmental factors. The decay rate is expressed as a half-life, the amount of time it takes for half of the original quantity of the isotope to disintegrate. The half-life of carbon-14 is 5,730 years.
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On the other hand, the quantity of carbon-14 available to be incorporated into living things does vary over time. Carbon-14 is produced from nitrogen when cosmic rays from space bombard Earth’s upper atmosphere. Fluctuations in the strength of Earth’s magnetic field alter the amount of carbon-14 that is produced in the atmosphere, as do solar storms. Ice ages and other climate factors also must be considered in carbon dating because they affect the global carbon cycle—the movement of carbon among the atmosphere, land plants and animals, soil, the surface, and deep oceans and marine sediments. Because of these factors, radioactive carbon decay must be calibrated. A graph is used to compute the “true” calendar age from the age that carbon-14 dating provides. The graph is generated from samples that can be independently dated using carbon-14 and at least one other method, such as layers in ocean sediment cores or ice cores; tree growth rings (dendrochronology); or, in the case of mineral formations in caves, the decay of another radioactive element, uranium, which is deposited from ground water. Scientists continually use new data to improve the calibration graph, and artifacts up to approximately 50,000 years old can now be reliably dated using carbon-14. Many different long-lived radioactive isotopes can be used for radiometric dating, and there is relatively good agreement between ages calculated using the decay of different isotopes.
Old as the hills What are the oldest possible estimates of Earth’s age? Rocks greater than 3.5 billion years old have been found on every continent. The oldest-known Earth rocks (4.03 billion years old) are in the Acasta Gneiss formation, near Great Slave Lake in Canada’s Northwest Territories. Therefore, the lower limit of Earth’s age is 4.03 billion years because the planet must be at least as old as its oldest rock formation. The ages of rock formations cannot be used to establish an upper limit for the age of Earth because complex processes are constantly Download at www.wowebook.com
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reshaping Earth’s surface. Sediments from the weathering of rock are deposited and eventually form sedimentary rock. Plate tectonics is also continually breaking down and regenerating Earth’s crust. Crystals of zircon as old as 4.4 billion years have been discovered in younger rocks in Western Australia. From the chemistry of the zircon crystals, researchers concluded that they had originally formed in magma that was in contact with water as it cooled. This suggests that Earth was already formed and had oceans 4.4 billion years ago. Extraterrestrial rocks provide information about the age of the solar system and place an upper limit on the age of Earth. The oldest rock returned to Earth from the moon is more than 4.4 billion years old. Most meteorites are primitive rocks from the early solar system that escaped accretion into planets. The oldest meteorites are 4.57 billion years old. Therefore, 4.57 billion years is the current upper limit on the age of Earth. Early estimates of Earth’s age were based on calculations of how fast a body of Earth’s size could be expected to cool after its formation. In 1846, the physicist Lord Kelvin concluded that Earth was just a few hundred million years old. At the time, radioactivity had not been discovered. Radioactivity provides a source of heat that Kelvin did not factor into his calculations.
Planetary heft How much does Earth weigh and how was its weight calculated? Earth weighs 6,000,000,000,000,000,000,000 (yes, that is 21 zeroes) metric tons. Earth is the largest of the four rocky planets (Mercury, Venus, Earth, and Mars). Jupiter is the giant of the solar system, with a mass more than 300 times that of Earth. A planet’s mass is directly related to its gravity. Because the force of gravity on Earth is known, it is possible to use Newton’s law of universal gravitation to determine Earth’s mass. Scientists can measure the mass of other planets by sending a spacecraft to pass near the planet and measuring the deflection of the spacecraft caused by the planet’s gravity.
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Alternatively, for a planet with a moon, it is possible to calculate the planet’s mass using Newton’s form of German mathematician Johannes Kepler’s third law of planetary motion. This equation relates the mass of a planet, the length of time it takes the planet’s moon to orbit around the planet, and the distance between the planet and its moon.
Graceful gravity Regarding the pair of satellites that are measuring changes in gravity on Earth, has the huge dam built in China affected gravity and the tilt of Earth’s axis? The twin satellites of the Gravity Recovery And Climate Experiment (GRACE) were launched in 2002, just before China’s Three Gorges Dam was completed (construction lasted from 1994 to 2003) and before the filling of the reservoir behind the dam had begun. Since then, GRACE measurements have indeed been able to track the accumulation of water mass behind the Three Gorges Dam. The satellite mission has also provided insights into groundwater storage and depletion in other regions, including the Congo, Mississippi, Amazon, and Lake Victoria basins. It is especially useful for monitoring underground aquifers, which are expensive to study using other means. GRACE is revealing rich detail about how Earth’s gravity field changes over time. Besides tracking groundwater storage and runoff on land, the mission is measuring changes in the mass of polar ice caps, variations in surface and deep ocean currents, ocean– atmosphere water vapor exchange, and movements within Earth that generate its magnetic field and others that shift the plates that constitute Earth’s crust. GRACE provides high-resolution global coverage every 30 days and less detailed coverage at submonthly intervals. The GRACE satellites revolve around Earth in tandem, one 220 kilometers (137 miles) behind the other. Local fluctuations in Earth’s gravity field affect the lead satellite first, moving it a tiny bit away from the trailing satellite. A microwave ranging system measures
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the distance between the two satellites every 5 seconds. The measurements of intersatellite distance are precise within 10 micrometers, less than the diameter of a human hair. The tilt of Earth on its axis is not something GRACE can measure, but calculations by NASA scientists suggest that the filling of the reservoir behind the Three Gorges Dam shifted the position of the North Pole by about 2 centimeters (0.8 inch). The shift in mass should also have increased the length of day by 0.06 microseconds. These changes in day length and wobble of Earth are tiny relative to normal variations in each, such as those caused by weather systems that alter the wet and dry areas of the world.
Throwing weight around Is Earth lighter or heavier than it was 50 years ago? With more people, is Earth heavier, or does that remain constant? And with man-made objects leaving the planet at an ever-increasing rate, does that make Earth lighter? Earth loses a very, very tiny amount of mass when spacecraft, such as the Vikings and Cassini, leave the planet permanently. The multiplication of earthlings does not alter the mass of Earth (assuming that we count the atmosphere as part of the planet’s mass). Biological processes simply redistribute mass. For example, we get our mass directly or indirectly from plants, which get their mass, through photosynthesis, from carbon dioxide and water. Three other processes do alter the mass of Earth, according to Tom Murphy, a physics professor at the University of California, San Diego, who studies the gravitational interaction between Earth and the moon to test Einstein’s theory of relativity. One of the three processes causes Earth to gain mass, but the others cause it to lose mass. First, Earth accumulates dust and rocks from space. Second, hydrogen and helium escape from Earth’s atmosphere. Third, radioactive elements within Earth decay. Helium is produced when certain elements decay. Decay also turns a small portion of the elements’ mass into heat, which radiates into space. The relationship
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between mass and energy is described by Einstein’s famous equation E = mc2 (energy released is equal to the mass consumed times the speed of light squared). Scientists think that Earth gains 10–100 tons of meteoric material (dust and rocks) each day. Murphy estimates that the amount of mass lost from the atmosphere when hydrogen and helium escape and from the decay of radioactive elements is less than the mass of the interplanetary dust gained. If this is true, Earth’s mass is slowly increasing. Yet, Murphy’s very precise measurements, which involve bouncing laser beams off the moon, have not detected a change in Earth’s mass. Although GRACE can detect local redistributions in Earth’s mass as the mission’s two satellites follow each other in identical orbits, GRACE cannot be used to measure the planet’s overall mass. Unlike local changes in gravity that affect the leading satellite first (slightly changing the distance between the leading satellite and its trailing partner, and making it possible to generate a gravity map), overall changes in Earth’s gravity would affect both satellites equally.
On the level When you hold up a carpenter’s level, with the bubble in the middle, what is it level to? Earth is round, so how can anything be level? When the bubble is centered, the carpenter’s level is parallel to a tangent to Earth at that location. A tangent is a straight line that touches a sphere at just one point. It makes a 90° angle with the radius of the sphere at that point. Because Earth is a bumpy sphere, the tangent is not always parallel to the ground itself. On a hillside, the tug of gravity is still toward the center of the planet, so the level will be aligned when it is perpendicular to a line to the Earth’s center.
Poolside Pythagoras Is the water in our 75-foot club swimming pool really as flat as it looks, or is it “round” like Earth and the oceans?
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Using a favorite theorem of geometry teachers, it is possible to determine Earth’s curvature along the pool’s length. The Pythagorean theorem states that the square of the length of the hypotenuse of a right-angled triangle is equal to the sum of the squares of the lengths of the other two sides—the height and the base. Because we want to know how much Earth curves along the length of a 75-foot swimming pool, the base of the triangle is 75 feet. The height is the radius of Earth, approximately 4,000 miles, beneath one side of the base. The third side, the hypotenuse, is a line between the far end of the base and the center of the Earth. The base is a tangent to the sphere where the base and height intersect at a 90° angle, but 75 feet away, the sphere curves away from the base. The length of the hypotenuse is the radius of Earth plus the distance between the surface of the sphere and the end of the 75-foot base line. Therefore, the length of the hypotenuse minus the radius of Earth is how much Earth curves along the 75-foot pool. Crunching the numbers results in approximately 0.0001 inches. So the pool is too short to see the curvature. Flat-Earthers and round-Earthers used “experiments on the convexity of water,” as biologist Alfred Russel Wallace called them, to argue their respective positions. In 1870, Wallace set a series of markers on the Old Bedford Canal in England. He claimed that his measurements proved Earth was round. But bending of light by the atmosphere can trip up such observations, and some flat-Earth proponents held their ground.
Magnetic personality When I was an undergraduate student, I learned that Earth’s magnetic core moved millions of years ago, and then it moved back to its present location. I also learned that Earth continued to move past its present axis to a horizontal position, and then it moved back to its present axis. Is there evidence that Earth moved near a horizontal axis? If so, was it because of Earth’s magnetic core?
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Earth’s magnetic field has reversed many times during the course of geological history, but scientists do not think that the reversals were caused by the core flipping over. The core cannot be a permanent magnet such as a refrigerator magnet because the temperature of the core is too high to sustain permanent magnetism. Instead, scientists think that the magnetism is generated through a dynamic mechanism called the geodynamo. Earth’s center is a solid inner core, surrounded by a liquid outer core. The geodynamo is the helical motion of the electrically conducting liquid-metal outer core. The buoyancy of lighter elements, rising heat, and the rotation of the planet are each thought to play a role in powering the geodynamo. Our knowledge about the geodynamo is mainly derived from computer simulations. These simulations show that any change in the flow of heat between Earth’s core and its mantle (the adjacent layer of Earth) can change the frequency of magnetic field reversals, although the exact mechanism of the reversals is not well understood. In terms of Earth’s tilt on its axis, of all the planets in the solar system, only Uranus has an axial tilt that is nearly horizontal (parallel to the plane in which it orbits around the sun). Earth’s tilt varies between 22° and 24.5°. Most of the other planets have more chaotic tilt variations, and the Earth may have had more chaotic tilt variations until the moon’s presence helped to gravitationally stabilize it. In addition to the tilt variations, Earth wobbles in a circle on its axis. Scientists have identified several overlapping wobbles with various causes. Because Earth is tilted to one side and is not a perfect sphere, the gravitational pull of the sun and planets differs at the two poles, which causes the tilt variations and one of the wobbles. Weather systems drive another wobble. Magnetic stress between the mantle, outer core, and inner core resulting from slight misalignments in the rotation of each region may account for another wobble.
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Flipping out As Earth approaches a magnetic shift, what effect will this have on electrical systems, and how will this affect the navigation of birds, sea creatures, and us when it reaches null? And what about the warming of Earth and incidence of skin cancer when our protective magnetic field is gone? The strength of Earth’s magnetic field has decreased about ten percent since 1845. Scientists think the polarity of the field might flip (magnetic north and south changing places) within a few millennia. The last flip occurred 780,000 years ago. Changes in the strength or orientation of Earth’s magnetic field could result from changes in the rotation rate or electrical conductivity of the molten iron in Earth’s core, which is thought to produce the field. Previous polarity reversals are documented in rock. For example, along the mid-Atlantic volcanic ridge where the continental plates are separating, stripes of rock with alternating polarity exist. Each stripe reflects the polarity of the field that existed when the rocks were made, because magnetic particles in molten rocks align with Earth’s magnetic field before the rocks solidify. The reversion of Earth’s magnetic field to zero during a flip could cause an increase in the amount of cosmic radiation reaching Earth’s surface, loss of protection from solar flares, and navigation problems of some organisms. Climatologists have failed to find evidence of changes in Earth’s temperature or weather patterns occurring in conjunction with magnetic reversals. The fossil record does not reveal any major changes in plant or animal life occurring in conjunction with previous polarity flips, suggesting that the increase in cosmic radiation did not lead to mass mutations. Even without Earth’s magnetic field, our atmosphere would still shield us from most cosmic radiation, but cancer rates could increase.
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Solar flares—streams of charged particles from the sun—already sometimes knock out power grids and satellite communications. Without Earth’s magnetic field to deflect the flares, they could cause even more trouble, including damaging the ozone layer. Many birds and sea creatures rely on the magnetic field to migrate, often combining magnetic cues with celestial cues (particularly, the direction the stars rotate) and—after their first migration— information about landmarks. No one really knows how these animals may adapt to a polarity flip, including possibly thousands of years when the magnetic field is zero. These creatures must have some adaptability, because our magnetic north pole has wandered about 700 miles since the 1800s.
A flat-out lie Why is it so common to read that Columbus’s contemporaries thought the world was flat? Modern scholarship says that neither Columbus nor his contemporaries (nor educated people in the Middle Ages) believed the world was flat. “The students are learning rubbish,” states an article in The Textbook Letter (January 1992), in critique of Earth science textbooks that teach students that no one was sure Earth was round until Christopher Columbus’s voyage in 1492 gave final proof. For those of us who dutifully learned the Columbus/flat Earth story in middle school, it comes as a surprise to discover that most historians consider it to be a myth. Texts from the Middle Ages generally describe Earth as a sphere and provide evidence such as this: One sees different stars at different latitudes, the hull of a departing ship disappears before the mast, and the shadow that Earth casts on the moon during an eclipse is consistent with Earth being a sphere. None of the early sources about Columbus’s voyage, including Columbus’s own Journal and his son’s account of the reasons for the voyage, raise any questions about Earth’s roundness. Columbus’s potential backers were indeed concerned about the feasibility of the voyage, but not because they worried about the ship Download at www.wowebook.com
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falling off Earth. Instead, they thought Columbus was drastically underestimating the distance to the Far East (which he was). An influential source of the Columbus/flat Earth myth is Washington Irving’s 1828 historical novel History of the Life and Voyages of Christopher Columbus. The novel’s dramatic scene of Columbus defending the shape of Earth against misinformed professors and clergy caused the flat Earth myth to enter the popular imagination. Although Irving appears to have fabricated the scene, other writers in the 1700s and 1800s had set the stage by beginning to underestimate medieval thinkers’ understanding of the world. In Inventing the Flat Earth (1997), Jeffrey Burton Russell posits that, in some cases, this was deliberate anticlerical propaganda. By Columbus’s time, the flat Earth was a minority view (at least, among the educated). His voyage probably did little to change the minds of any remaining flat-Earthers. After all, members of the twentieth-century International Flat Earth Society were unconvinced by photos from the space program.
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7 The heavens Here comes the sun How is the time of sunrise predicted? It does not usually occur at the time listed. The time of sunrise is calculated for a specific latitude and longitude from the speed of Earth’s rotation and revolution around the sun. You can use a computer program that does the sunrise calculations, the moon rise and set times, and a number of other astronomical applications at the U.S. Naval Oceanography Portal’s Web site (www. usno.navy.mil/astronomy). The calculations assume that your eye is on the surface of Earth, at sea level, with no landscape features obstructing your view of the horizon. The calculations also assume average atmospheric conditions when taking into account that Earth’s atmosphere bends the light from the sun, allowing us to see the top of the sun before it has risen above the horizon. Unpredictable variations in atmospheric conditions affect time of sunrise by altering how much the light is bent. Sunrise is defined as the moment when the center of the sun is 50 arc minutes below the horizon. An arc minute is one-sixtieth of a degree. Fifty arc minutes is the sum of the apparent radius of the sun (16 arc minutes) and the average amount of atmospheric refraction— the bending of light that allows you to see the top of the sun before it is really at the horizon (34 arc minutes).
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Fickle, fickle, local star My father, who is a retired naval navigator, told me that he remembers seeing a sunset and the beginning of a sunrise at the same time. He said that he was on a ship somewhere in the Pacific off Hawaii. I think this is impossible unless you were close to one of the poles. Is it possible? To see the sun setting and coming up at essentially the same time, the sun must be above the horizon when it reaches its lowest point in the sky and starts to rise. The only places this occurs are within the Antarctic Circle and the Arctic Circle around the time of their respective summer solstices. Your dad may not have been pulling your leg, though. Perhaps what he saw was a mirage of a double sun. Although rare, double sun mirages have been reported to occur when the sun is near the horizon and sunlight is refracted through a “lens” of low-density air. When it occurs, the secondary image usually appears above the sun.
Twilight zone Points above the Arctic Circle and below the Antarctic Circle have 24 hours of sunlight in the summer and 24 hours of darkness in the winter. How many days of 24 hours of sunlight and darkness are there? Does a transition period exist? A transition period exists between full darkness and full sunlight. The length of daylight, darkness, and the transition period differs depending on the latitude within the Arctic and Antarctic circles. The Poles are the extremes, with the greatest amount of full darkness and full sunlight, and the shortest transition in between. At the North Pole (the seasons are reversed at the South Pole), full darkness begins at the end of the first week in October and lasts until the first week in March (150 days of darkness). The period of full darkness—polar night—is followed by a period of twilight that lasts almost two weeks.
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Just before the spring equinox, the sun appears on the horizon and stays there all day. On the spring equinox, March 21, the sun rises above the horizon. It reaches its highest point in the sky on the summer solstice and sinks beneath the horizon just after the autumn equinox on September 22 (186 days of sunlight). Then nearly two weeks of twilight precede the transition to polar night. Twilight becomes paler in the days leading up to polar night and brighter in the days leading up to full sunlight—polar day—similar to the twilight we experience after sunset and before dawn each day. Twilight is caused by the reflection of sunlight off the upper atmosphere, which continues to receive direct sunlight when the sun is less than about 18° below the horizon. Between the Arctic Circle and the North Pole, the periods of polar night and polar day are shorter than at the Pole. Also, unlike at the Pole, during some periods the sun is above the horizon for part of the day. The situation is similar on the Arctic Circle, except that even on the winter solstice, when the sun is below the horizon for 24 hours, it is still visible for a couple of hours because of atmospheric refraction. On my midsummer backpacking trip to the land of the midnight sun, those of us who brought flashlights felt pretty silly. Although the period of full sun was over, it was still close enough to the summer solstice that a bright twilight lasted from sunset to sunrise.
It all adds up December 21 is the shortest day of the year, but it doesn’t seem to be the coldest. Why isn’t the day with the least sunlight the coldest? Winter solstice has the fewest hours of sunlight and the most diffuse sunlight (because the sun remains low in the sky), so it is the day the Northern Hemisphere receives the least amount of energy from the sun. It is not the coldest time of year because the Earth and its atmosphere store thermal energy; therefore, a net loss of energy accumulates over time. Even after December 21, the amount of heat radiating from the Northern Hemisphere is greater than the amount of heat arriving Download at www.wowebook.com
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from the sun. Therefore, the cooling continues into January and February, until the days lengthen enough that the energy input from the sun is greater than the Northern Hemisphere’s energy output. Similarly, the dog days of summer usually occur a month or so after the summer solstice because thermal energy continues to accumulate if energy input is greater than energy output. The same effect is observable on a daily basis. Normally, the hottest part of the day comes after midday because incoming solar energy during the afternoon is still greater than that radiating back to space, and the air, ground, and water continue to warm. The input and output of thermal energy determine the average temperature for the time of year, but the movements of air masses determine the weather on any given day in a particular location.
As the world turns Summer solstice is the day that has the longest daylight hours. But the earliest sunrise happens before June 21. Why don’t the earliest sunrise, latest sunset, and longest daylight occur on the same day? Earliest sunrise, latest sunset, and longest daylight would occur on the same day if we used sundials to tell time. Modern timekeeping devices assume that each day is 24 hours long, but this is an average. Near summer and winter solstice, sunrises are separated by slightly more than 24 hours. Therefore, although each day leading up to summer solstice has more daylight as the sun gets higher in the sky, the time of dawn and dusk is pushed forward (later) according to our watches because each day lasts longer then 24 hours. Days would all be the same length if Earth were not leaning like the Tower of Pisa, and if it had a perfectly circular orbit around the sun. Length of daylight would not vary during the course of the year, either. Instead, because of the 23.5° tilt of Earth’s axis, the sun traces a path from south to north across the sky between winter and summer solstice. During that time, Earth revolves halfway around the sun,
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and the sun moves from being directly overhead at the Tropic of Capricorn (23.5° south) to being directly overhead at the Tropic of Cancer (23.5° north). The Latin roots of the word solstice mean “sun stationary.” Earth does not stop revolving around the sun at the solstice, but the apparent north–south motion of the sun ceases. Similar to the top or bottom of a Ferris wheel, the motion is horizontal instead of up or down. Near the solstice, all the motion of the sun from the revolution of Earth is parallel to the equator (eastward). The motion of the sun from the revolution of Earth is in the opposite direction to the westward motion of the sun from the rotation of Earth. Earth takes only 23 hours and 56 minutes to spin 360°, but it takes an average of 24 hours for Earth to rotate far enough around its axis to compensate for the revolution of Earth around the sun. At the solstice, the motion from the revolution is due east instead of northeast or southeast, so Earth must rotate farther than usual to reach the next sunrise, which is the reason the day is longer than 24 hours near the solstice.
To leap, or not to leap? I have noticed that the winter solstice keeps moving earlier. I read recently that the winter solstice used to fall on New Year’s Day, slowly moved over the centuries to December 25 and now is December 21. With the addition of February 29 every four years, and the addition of 1 second this year, why doesn’t the calendar keep the winter solstice on January 1? December 25 was set as the winter solstice in the Julian calendar, the calendar introduced by Julius Caesar. Until the Gregorian calendar—the calendar we use today—replaced the Julian calendar, the solstices and equinoxes moved earlier by about three-quarters of a day each century. Because the shift affected the date of Easter, Pope Gregory XIII reset the spring equinox to March 21 by deleting ten days from the year 1582 and changed the leap year system. In the Gregorian calendar, the Download at www.wowebook.com
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Northern Hemisphere’s winter solstice falls between December 20 and December 23, usually on December 21 or 22. Because increasing daylight follows the winter solstice, some cultures associate it with rebirth and renewal, and they celebrate it as the calendar New Year. The Julian calendar has a leap year every four years because the Romans believed that the solar or tropical year—the length of time between one spring equinox and the next—was 365.25 days. The tropical year is actually 365.2422 days. The day length in the Gregorian calendar is 365.2425. The Gregorian calendar gets tighter agreement between the calendar year and tropical year by deleting some leap years. Leap years still occur in years divisible by four, but a century year is a leap year only if it is divisible by 400. It should take nearly three millennia to accumulate an error of one day in our calendar. However, the length of the tropical year is not constant. The day is slowly lengthening as Earth’s rotation slows. A leap second is added every couple years to compensate. More significantly, as the rotation slows, Earth’s precession—wobbling similar to a spinning top—grows. Increasing precession slightly shortens the tropical year. Without precession, Earth would have to revolve a full 360° around the sun for its axis to be tilted the same direction relative to the sun—for example, with the Northern Hemisphere tilted away, as at winter solstice. With precession, Earth revolves slightly less than 360° to return to the same position relative to the sun (at which point it is not quite back to the original position with respect to the background stars). But even with increasing precession, many generations will pass before our descendents need to skip a leap year.
Just counting the days I’ve always wondered why we don’t have a 13-month calendar. Wouldn’t it make more sense to have twelve 28-day months and one 29-day month, not counting leap years? Or would that scenario eventually lead to the seasons marching out of sync with the solar year?
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The Calendrier positiviste, proposed by French philosopher Auguste Comte, divided the year into 13 months of 28 days each. The remaining day (or two days in leap years) was placed at the end of the year and was not assigned to any week or given a weekday name. Therefore, in Comte’s perpetual calendar, the days of the week fall on the same dates each month. Such a calendar is synchronized with the solar year as long as the number of leap years is adequate. But on the basis that man is supposed to rest every seventh day, some religious leaders object to the inclusion of days that are not part of any week. Today the main roadblock to any type of calendar reform is the cost of changing all those lines of computer code. It would be Y2K on steroids. Another daunting challenge is agreeing on a new calendar. When the League of Nations appointed a Committee of Inquiry into Calendar Reform, it received 185 proposals from 38 countries, according to E. G. Richards’ Mapping Time: The Calendar and Its History (Oxford University Press, 2000). Even today, multiple calendars are in use for keeping track of cultural and religious events. For example, the Islamic calendar is strictly lunar, consisting of 12 months of 29 or 30 days. Because it is shorter than the solar year, the Islamic calendar begins earlier with respect to the seasons each year. The Jewish calendar is lunisolar—synchronized with the moon and sun. It is based on the lunar month (29.53 days), but it is kept in sync with the solar year through the addition of a 13th month to 7 out of every 19 years. Different lunisolar calendars are in use in China and India. The Gregorian calendar, which serves as the international standard, is a solar calendar based on the Julian calendar—named for Julius Caesar. The Julian calendar was rooted in an older Roman calendar, which was lunisolar. When Caesar overhauled the calendar, he gave up linking it to lunar cycles. Therefore, our calendar developed through a series of patches to older versions, vestiges of which are apparent not only in the calendar’s complexity, but also in the inappropriate naming of the months. September, October, November and December mean, respectively, seventh, eighth, ninth, and tenth month.
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’Tis the season I have always thought that our current seasons’ beginning dates are 45 days off. The longest day of the year (summer solstice) ought to be the middle of summer instead of the first day of summer. The shortest day of the year ought to be midwinter. How did our current seasonal dates get established? Archeological evidence shows that the solstices and equinoxes, especially the winter solstice, had significance back in Neolithic times. Yet despite what many books and calendars say, even today the equinoxes and solstices are not universally accepted as the seasons’ beginnings. These sources seem to have adopted a convention in the absence of any official decree. In fact, the National Oceanic and Atmospheric Administration (NOAA) National Weather Service in Washington D.C., uses a different definition of the seasons. According to its Web site, “Meteorological autumn (different from standard or astronomical autumn) begins September 1 and ends November 30.” Winter is December, January, and February. Spring begins on March 1, and summer begins on June 1. Weather records are easier to keep when using the meteorological definition of the seasons, especially because the dates of the solstices and equinoxes vary. Also, in most locations, meteorological winter is usually the coldest period of the year, and meteorological summer is the warmest. Although weather tends to worsen after winter solstice, many cultures have traditionally celebrated it as midwinter and the summer solstice as midsummer. For these cultures, the seasons begin on the cross-quarter days, which are in November, February, May, and August, halfway between the solstices and the equinoxes. In the ancient Celtic calendar, the November cross-quarter day was celebrated as the Festival of the Departing Sun, and the Celts lit bonfires and dressed in scary costumes to prevent evil spirits from rushing in. Of course, this tradition lives on in young North American ghouls and goblins at Halloween.
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We celebrate another of the cross-quarter days as Groundhog Day. But if you take winter solstice to be midwinter, then you don’t need to rely on Wiarton Willy or Punxsutawney Phil to find out if winter is over. The February cross-quarter day marks the beginning of spring.
Smoke and mirrors Rainbows and fogbows fail to get closer as you travel toward them, in the same way mirages of water on a highway remain off in the distance because they are not really “there.” Can rainbows and fogbows be considered mirages? Mirages, rainbows, fogbows, and coronae—faintly colored rings around the sun and moon—are among the many visual spectacles that are caused by the interaction of light with components of the atmosphere. Each phenomenon results from a specific type of interaction between light and matter. Colloquially, mirage is sometimes used to refer to an illusion of any kind. Scientifically, however, mirage denotes an optical phenomenon caused by the refraction or bending of light as it passes through atmospheric layers of different density. Atmospheric refraction is constantly making objects appear shifted, but usually the shift is unnoticeable. In the case of a mirage, the shift is great enough to make it seem that an object has a copy in a different location. The highway mirage or desert mirage—in which a shimmering effect is observed on a road or sand—is common, especially on sunny days. It occurs when the layer of air adjacent to the ground becomes significantly warmer than the air higher up. Light passing into warmer (lower-density) air increases in speed and bends. As a result, rays of light that would have traveled straight from the sky or an object to the ground instead arc upward. An observer in the light’s path sees what is called an inferior mirage—a mirror image of the sky or object that seems to have come
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from below the actual object. Turbulence in the air makes the image shimmer, giving it the appearance of being reflected in water. A mirage that appears above the actual object is called a superior mirage. It results from a temperature inversion—warmer air above cooler air—that bends the light rays downward, making them seem to have come from higher up. More complex layering of warm and cold air leads to the formation of a collage of mirages called a fata morgana. Rainbows, fogbows, and coronae involve water droplets. Rainbows and fogbows are produced when light enters and reflects off the back of a water droplet. Refraction that occurs as the light enters and exits the drop disperses light into its component colors. Coronae around the sun and moon form when tiny cloud droplets, ice crystals, or dust particles obstruct light. The light waves create patterns as they bend around the obstruction and interfere with each other.
Elusive pot of gold Why is the inner sky of a rainbow lighter in color than the sky above the rainbow? Although we perceive a rainbow as a colored arc, it is really a disk of light. The center of the disk—the antisolar point—is opposite the sun. We see more of the disk when the sun is lower in the sky, but we cannot see the entire rainbow disk (except sometimes from an airplane) because Earth is in the way. Both the colored edge of the rainbow and its bright center are caused by the refraction (bending) and reflection of sunlight by raindrops. When sunlight enters a raindrop, the light bends. The degree of bending depends on the wavelength of the light. Thus, similar to a prism, a raindrop disperses white light into its component colors. The light is then reflected off the curved, mirrorlike surface of the back of the raindrop. As it exits the front of the raindrop, the light is bent again, and its component colors become more spread out.
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Red light deviated 138° from its original path reaches an observer’s eyes from raindrops on the outermost edge of the rainbow. At the eyes of an observer, a line to the top of the red arc makes a 42° angle (180°–138°) with a line between the sun and the antisolar point (which is also the line between one’s head and one’s shadow’s head). Shorter-wavelength violet light is bent more than longerwavelength red light. The top of the violet arc is at 40°, and the other colored arcs are between 40° and 42°. Raindrops in the remainder of the rainbow disk send light rays deviated through larger angles (up to almost 180°) to an observer’s eyes, but the different colors of light mix together to give white light. So the center of the rainbow disk is bright. The raindrops outside those creating the red arc do not send light to an observer’s eyes. So the sky outside the rainbow is dark. When some of the light entering raindrops undergoes two internal reflections instead of one, these light rays exit the drop more deflected from the horizontal. This creates a second rainbow between 50° and 53°. The two internal reflections cause the colors to be flipped around so that violet is on the outside of the secondary rainbow and the sky above the rainbow is bright. On the other hand, raindrops between 42° and 50° do not send light to our eyes, giving rise to an effect (dark sky between the two rainbows) called Alexander’s dark band. In a different location, a different set of raindrops sends the light to an observer’s eyes and is responsible for the rainbow. So “chasing rainbows” is another expression for a futile effort—a rainbow does not have a physical location in the sky.
Over yonder Can a formula tell you how far away the horizon is based on how far above sea level you are? I have heard that when a person stands on the beach, the horizon is 3 miles away.
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A simple approximation for the distance to the horizon is the square root of 1.5 times the height (in feet) of your eyes above sea level. This calculation works for anywhere on Earth, even from the top of Mount Everest. However, if you have plans to visit another planet or the Little Prince on his home asteroid, B612, you will need to take the planet’s radius into consideration. The simple and the full distance calculation both use the good old Pythagorean theorem—the square of the length of the hypotenuse is equal to the sum of the squares of the other two sides. If Earth is taken to be a perfect sphere and the horizon is at sea level, the point on the horizon along your line of sight, your eyes, and the center of Earth are three corners of a right triangle. The hypotenuse is the distance from the center of Earth to your eyes (the radius of Earth plus your height above sea level). The other two sides are the radius of Earth (beneath the horizon) and a line from your eyes to the horizon. Therefore, to get the distance to the horizon, add the square of your height above sea level (h) to two times your height times the radius (r) of Earth (which, near the equator, is 6,378 km or 3,963 miles) and take the square root of the result. That is, distance = the square root of (h2 + 2rh). The simplified formula begins with dropping the h2 term (the square of the observer’s height above sea level) because it is negligible compared to the radius of the planet (r) times the observer’s height above sea level. Then a little number crunching can reduce the 2rh term. Earth’s radius (3,963 miles) is substituted in and divided by 5,280 feet per mile. This simplifies the terms under the square root sign to 1.5 multiplied by the observer’s elevation. The nifty thing is that the numbercrunching step also takes care of converting units, so plugging in the observer’s elevation in feet yields the distance to the horizon in miles. The calculation results in the horizon being approximately 3 miles away for a tall person (whose eyes are 6 feet off the ground) standing at sea level.
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Details, details I am a private pilot and am interested in approximate distance to the horizon depending on my height above ground level. This is important if a pilot loses engine power and needs to coast to an emergency landing area. I found your column calculating the distance to the horizon very interesting and useful. However, how can you assume that the angle at the horizon point will always be 90°? An observer’s line of sight to the horizon is a tangent—a line that touches a sphere at only one point—to Earth. By a very old theorem in geometry, the tangent and radius of the sphere make a 90° angle at the point of contact of the tangent. This equation disregards Earth’s bumps and equatorial bulge. It also ignores the refraction, or bending, of light by Earth’s atmosphere. Air is usually densest near the surface, which makes the light rays arc upward between Earth and an observer and makes it possible to see slightly (usually a few percent) farther. Refraction is the main limitation to the accuracy of global positioning satellites. The amount of refraction varies by day and at different locations, depending on the temperature gradient of the atmosphere, especially the lower atmosphere.
Clouds’ illusions One morning I woke to find clouds rolling over the top of Ute Mountain, a nearby peak that stands almost 10,000 feet. Although the mass of them disappeared, a solitary banner-shaped cloud remained hanging on to the very top of the mountain and flying in the direction of the wind. It appeared to be in perpetual motion while refusing to let go of the peak and never changing length. What was forming the stationary cloud?
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It formed as a result of orographic lift—an air mass being forced from low to high elevation as it passes over the mountain. Orographic lift plays a critical role in weather patterns in mountainous regions around the world. When air masses pass over mountain ranges, water is not “squeezed” out of the air, as weather forecasters sometimes say. Air is not like a sponge. Instead, the water molecules, which are in a constant state of evaporation and condensation, slow down as the temperature decreases, and condensation starts to outpace evaporation. In addition to influencing precipitation patterns, orographic lift leads to the formation of strange clouds because the change in speed and direction of the air blowing over mountains can produce standing waves in the atmosphere. Atmospheric standing waves are patterns of variation in the pressure and temperature of the air. The waves can remain nearly stationary for extended periods if the wind generating them has a fairly constant speed. Banner clouds are produced when a sustained drop in pressure occurs behind the mountain obstacle. The drop in pressures causes the air to expand. Expansion of the air causes it to cool (a phenomenon put to practical purposes in refrigerators and air conditioners) because heat energy is used to overcome the weak attractive forces between the molecules in the air. Banner clouds are similar to the condensation trails that form as air passes over the wing of an airplane. Condensation forms continuously in the low-pressure region and evaporates beyond it. Lenticulars (Altocumulus Lenticularis) are another interesting type of cloud caused by atmospheric standing waves over mountains. These striking, lens-shaped clouds are sometimes mistaken for UFOs.
Dust at dusk Why does the sky change colors in the evening?
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Sunlight is composed of light in all the colors of the rainbow, which can be seen by passing it through a prism. Gas molecules and small particles in the atmosphere scatter sunlight, and higherfrequency blue light is scattered more than lower-frequency red light. In the evening, sunlight passes through more of the atmosphere than it does at midday. As more of the blue light is scattered, the light from the sun that reaches your eyes changes from yellow to red. To understand why the sun passes through more of the atmosphere in the evening, draw two concentric circles, one to represent Earth and one to represent the atmosphere. Draw a straight line from “Earth” at the 12 o’clock position through to the atmosphere; this approximates the path of the sun’s rays at midday. Now draw a line from the same point on the Earth circle to the 3 o’clock (or 9 o’clock) position on the atmosphere to approximate the path of the sun’s rays as the sun is sinking below the horizon. You can see that the rays traverse more of the atmosphere in the evening than at midday. In reality, the atmosphere acts similarly to a giant lens and bends the light of the sun, so the effect is even greater than your sketch shows. If the amount of atmosphere traversed by the sunlight were the only important factor, the morning sky and night sky should look similar. More particles (such as dust, soot, pollen, and salt from the oceans) are usually found in the atmosphere in the evening than in the morning. Human activities produce pollutants and stir up particles during the day, and winds tend to die down at night, allowing some of the particles to settle by morning. When many small particles, such as ash from volcanoes or wildfires, scatter sunlight, the morning sun may take on an apocalyptic-looking red glow.
Green flash with envy Does the green flash exist? I’ve watched thousands of sunsets and have never seen it. My sister came to visit and said, “I think I’ll go down to the beach and look for the green flash,” and returned a few minutes later saying, “I saw it.” Why can one person not see it and another person shout, “There it is!”?
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At sunset, the top edge of the sun can appear bright green for a second or two. Some people have conjectured that this so-called green flash is an optical illusion caused by the red light from the setting sun bleaching the red-sensitive pigment in the retina. As a result, contrast effects in our visual systems can make the last rays of the setting sun appear green. The optical illusion may trick some people into thinking they have seen the green flash when they really have not. However, the green flash is a real phenomenon that can be photographed. It is also possible to see the green flash at sunrise before the sun is above the horizon and when pigment bleaching would be insignificant. The green flash is a fickle phenomenon that depends on a combination of refraction (bending), scattering, and absorption of light. As light passes through the atmosphere, it is slowed and bent. This causes the different wavelengths, or colors, to separate as they do in a prism. A series of tightly overlapping different-colored suns results, with red lowest in the sky, yellow slightly higher, green above yellow, and blue above green. At sunset, the atmosphere usually scatters most of the blue light and absorbs most of the yellow. Therefore, as the red sun sets below the horizon, a narrow upper rim of the green sun is all that remains. Because the separation of colors is so small, the green flash is not easy to see unless a mirage occurs, such as the kind of effect that creates the impression of puddles on a hot highway. This type of mirage occurs as light rays passing from a higher, cooler layer of air to a lower, warmer one are bent upward from their path. It magnifies the green flash because, as the sun sets with only its upper green rim visible, the mirage is producing a second inverted green rim just below and adjoining it. For more information and animations, see the Web site by astronomer Andrew Young at San Diego State University, http://mintaka.sdsu.edu/GF/.
Moon moniker Charon, Deimos, Europa, Phobos .... Every moon in our solar system has a name except our own. What gives? Download at www.wowebook.com
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Actually, we refer to other planets’ satellites as “moons” by analogy to our own moon. The Greeks called our moon Artemis, and the Romans called it Luna (from which we get the word lunar). The International Astronomical Union is responsible for deciding the names of celestial bodies, but I don’t envision us breaking the habit of calling it “the moon.” Think of all the songs and poems we would have to rename.
Pink Floyd’s fib What feedback mechanism keeps one face of the moon pointed at the Earth? Somebody told me it’s the ocean tides. The moon rotates once on its axis in the time it takes to revolve once around Earth. Therefore, the same face of the moon is always pointed toward Earth. It is not a strange coincidence that the moon’s rotation and revolution are synchronized. Most of the other moons in the solar system are likewise synchronized with their planets. The synchrony is related to tides, or at least the same forces that cause tides. The gravitational tug of Earth warps the moon, creating a tidal bulge on the side facing Earth. Billions of years ago, when the moon rotated more quickly than it does now, the tidal bulge would get ahead of the Earth–moon line. But the Earth would tug back on the offset bulge, slowing the moon’s rotation. Over millions of years, these forces synchronized the moon’s revolution and rotation so that one side is always facing in our direction and the other side is always facing away from us. The side facing away from us has sometimes been dubbed “the dark side of the moon,” but that is a misnomer. It gets the same amount of sunlight as the side facing Earth. When we have a dark “new moon,” the other side of the moon is fully illuminated. Over time, we actually see slightly more than half of the moon’s surface because rotation and revolution are not constantly synchronous. The moon’s revolution speed changes depending on where it is in its elliptical orbit. Revolution slows when the moon is farthest from Earth and speeds up when the moon is closest to Earth. As rotation
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gets a bit behind or ahead, slightly different sections of the sphere face our direction.
When the moon hits your eye Please explain why the sun and moon appear larger when they are near the horizon than when they are overhead. This appears to be an optical illusion because they subtend the same angle regardless of position. About 350 BC, the Greek philosopher Aristotle ascribed the enlarged appearance of the horizon moon to magnification by the atmosphere. To this day, atmospheric magnification remains a popular, albeit incorrect, explanation. Bending of light by Earth’s atmosphere does affect the way we see celestial bodies on the horizon. Bending of light can make the setting (or rising) sun or moon appear oval because light from the bottom of the setting sun is bent through more of the atmosphere than light from the top of the sun. This slightly squashes the sun or moon vertically without changing its horizontal dimension, and, therefore, fails to explain the enlargement. Scientists now agree that the enlargement is an illusion, but they are still arguing about how our perceptual systems play this trick on us. You can convince yourself that it is an illusion by measuring the raised and horizon moon with calipers or a ruler held at arm’s length. For most people, viewing the horizon moon upside down also eliminates the illusion. Helen Ross and Cornelis Plug, the authors of the book The Mystery of the Moon Illusion (Oxford University Press, 2002), conclude that the illusion is probably the combined effect of several factors, including terrain. On the horizon, we mentally compare the size of the moon with trees and other landscape features. Experiments to block out or manipulate the appearance of the terrain using mirrors can change the perceived enlargement by 26 to 66 percent. Yet the moon illusion can also occur when the horizon is featureless, such as over the ocean.
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Simply looking upward by raising your eyes or tilting your head reduces the perceived size of artificial moons in experiments. Why our visual systems do this is uncertain, but it may cause the overhead moon to appear up to 10 percent smaller than the horizon moon. Another factor that may contribute to the illusion is the difference in color between the horizon and overhead moon caused by light travelling through more of the atmosphere when the moon is on the horizon. The Mystery of the Moon Illusion rules out several explanations for the enlargement, including a popular one that it is because we perceive the sky as a flattened dome. The authors conclude that the sky does not always appear flattened and that explaining one illusion with another illusion is dubious. So after more than two millennia of arguments and experiments, the man in the moon is still teasing us.
It’s just a phase When the sky is still relatively light, you can sometimes see a nice view of the moon reflecting back less than full. It looks oblong, but we know the moon is really round. Why doesn’t the rest of the moon that is not reflecting sunlight show up as a dark part against the light sky behind the oblong? The moon you describe, when direct sunlight is illuminating more than half but not the entire side of the moon we can see, is in the gibbous phase. The sun always illuminates half of the moon’s sphere, just as the sun always illuminates half of Earth. The phases of the moon occur because, at different times in the 29.5-day lunar cycle, we see varying portions of the illuminated half. We see a full moon when the sun and moon are in opposite directions from Earth. We see a new moon, the entire unlit side, when the sun and moon are in almost the same direction from Earth. We see a quarter moon, half of the lit side, when the sun and moon are about 90° apart in the sky.
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It is easy to visualize why we see the different fractions of the lit face by setting up a flashlight beam (sun) and holding a ball (moon) at arm’s length in front of you (Earth). Turn to face the sun, face perpendicular to the sun, and face away from the sun. Be careful not to get between the sun and moon, or you will cause a lunar eclipse. A common misconception is that the phases of the moon are caused by Earth’s shadow falling on the moon. This is a lunar eclipse and occurs only when the sun, Earth, and the moon line up precisely. During a lunar eclipse, the moon passes through Earth’s shadow in less than two hours. The nonilluminated part of the moon is visible only when sufficient contrast exists for our eyes to detect it. During a solar eclipse, we can see a dark moon in front of a bright sun. On a very dark night, we can distinguish the new moon, faintly illuminated by earthshine— reflected sunlight from Earth. During the day, the bright blue sky (produced by the scattering of sunlight by Earth’s atmosphere) drowns out the faint earthshine reflected by the moon, so we can see only the fraction of the moon that is more strongly illuminated by direct sunlight.
Conspiracy claims Can telescopes on Earth see the lunar landing site(s)? A lot of noise and misinformation exists about government cover-ups and Hollywood simulations, but can anyone with a powerful enough telescope prove that it is there? Various pieces of equipment, such as the lander platforms and moon buggies, were left behind at six landing sites on the moon. The largest among these objects, the landers, are just 9 meters (30 feet) across. None of our current telescopes is powerful enough to detect them. Even in an image from the Hubble telescope, they are smaller than a single pixel. Hubble can distinguish only things on the moon that are more than 60m wide. Suitcase-sized reflectors placed on the moon during the Apollo missions can be detected (albeit not seen) from Earth. Scientists bounce lasers off the reflectors to measure the distance between Earth and the moon. However, those who maintain that humans
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never set foot on the moon argue that a secret robotic mission delivered the reflectors. NASA’s Web site has images of the moon landing sites taken recently by the Lunar Reconnaissance Orbiter. You can just make out the landers and a footpath the astronauts traced in the moon dust. The images may not satisfy the moon hoax proponents. After all, the original photographs supplied much of the purported evidence that NASA faked the moon landings. For example, the lack of stars and the tricks of light and shadows are said to be evidence of a hoax. On the contrary, these oddities are consistent with the photos being real. All the missions took place in the morning of the lunar day, which lasts 29.5 Earth days. The sun is shining, but the sky not directly illuminated by the sun appears black because no atmosphere exists to scatter incoming sunlight. With a camera set for daytime exposure, the stars are too faint to be seen. Likewise, the fact that shadows are not completely black on the moon is not evidence of air in a Hollywood studio scattering light from a spotlight. The lunar surface itself reflects light. Backscatter— the reflection of light back in the direction from which it came—is particularly strong. Strong backscatter is also the main reason the full moon—during which the sun, Earth, and the moon are in line— appears about 10 times as bright as a half moon.
Moon mine Why does the moon have more helium-3 than the Earth? Might helium-3 be valuable enough, possibly for controlled nuclear fusion, to extract it from the moon, as done in the film Moon?
Helium-3 (the rare, lightweight relative of the helium-4 we use to fill balloons) is carried by the solar wind. Earth has a strong magnetic field that deflects most of the solar wind particles. In contrast, because the moon lacks a magnetic field and an atmosphere, the elements carried by the solar wind become implanted in the moon’s surface. Lunar soil samples collected by the Apollo astronauts revealed that helium-3 is more abundant on the moon than on Earth. A recent
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computer simulation estimated that the relative abundance is approximately 30,000 to 1. The simulation—which accounted for the solar wind strength, the shielding effect of Earth’s magnetic field tail on the near side of the moon, and the mineral composition of the lunar soil—also calculated that more helium-3 exists on the lunar near side than the far side because of the distribution of ilmenite, which is the only lunar mineral that traps helium-3 effectively. Helium-3 has been touted as an ideal fuel for nuclear fusion. Nuclear fusion powers the stars and has the potential to be a clean, sustainable source of power for earthlings. The International Thermonuclear Experimental Reactor (ITER) is designed to make that potential a reality in the next three decades. Success is not a given: Fifty years ago, practical nuclear fusion was predicted to be five decades off. ITER uses the fusion of deuterium (a heavy isotope of hydrogen) into helium-4. An intermediate step in this reaction is the formation of tritium, a radioactive isotope of hydrogen. This fusion process also forms a high-energy stream of neutrons. Because tritium is radioactive, and because neutrons are highly destructive to the reaction vessel, containment is a considerable challenge. On the other hand, helium-3 is not radioactive, and the fusion of helium-3 does not produce radioactive intermediates or neutrons. A small helium-3 fusion reactor has demonstrated the feasibility of helium-3 fusion; yet, as with deuterium fusion, it currently takes a greater input of energy to drive the fusion reaction than is harnessed from the fusion process. Therefore, creating a prototype fusion power plant is the greatest hurdle to bringing Moon out of the realm of science fiction. Mining the moon for helium-3 is theoretically, although not currently, economically feasible. To make fusion a significant source of power, surface rock from enormous swaths of the moon would need to be collected and processed.
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Lost Luna Looking at the moon, I was wondering whether Earth would be any different without it? Could we get along okay without it being there? It is hard to imagine that we could be the same without “Blue Moon,” “Bad Moon Rising,” “Moon River,” and the whole kit and caboodle of moon-inspired songs, poetry, artwork, and folklore. But lunacy aside, the moon actually exerts a powerful stabilizing force on Earth. Some researchers even think that, without our natural satellite, we would not be around to contemplate a moonless sky. The angle at which a planet’s spin axis is tilted is usually strongly influenced by small chaotic motions in the planet’s orbit around the sun. The tilt of Mars’ spin axis is extremely erratic over multimillionyear time scales because the tiny satellites around Mars are not large enough to stabilize its tilt. The flip-flopping of Mars’ tilt would have sometimes brought more sunlight to the poles than the equator, causing the Martian climate to fluctuate wildly. In Earth’s case, its moon is large enough to exert a substantial torque on the planet. The force causes Earth’s spin axis to rotate, or wobble, in a circle similar to a spinning top. The wobble is small and takes about 26,000 years to complete, but that is large enough to stabilize the tilt of Earth’s spin axis by drowning out the effects of the other planets’ gravitational influences. By stabilizing the tilt, our moon acts as a climate regulator, and it may have facilitated the emergence of life on Earth. The moon may also have influenced geological processes on Earth. Earth’s crust moves similar to an enormous, slow conveyor belt. Volcanic activity at the center of the Atlantic Ocean generates new crust, and old crust is recycled when it plunges into deep trenches in the Pacific Ocean. Some researchers propose that the moon’s gravitational tug on Earth may have initiated the rolling motion of Earth’s crust.
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The moon’s gravitational pull also causes tides. The sun also causes tides, so tides would still exist without the moon, but they would be about half the size. Tidal friction is slowing the rotation of Earth. It may seem as if there are never enough hours in the day, but the tug of the moon is making the days longer. True, it is only by about 2 milliseconds per day, but it means that, every year or two, a leap second is added to our timekeeping.
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8 Far out Deep impact Not long ago, I read that a humongous asteroid was headed toward Earth within the next five years. The article, quoting a renowned scientist, warned that time was running out to either blast it to pieces or deflect it because it would take years to develop and build the solution. I’ve seen no follow-up on this information. Are our statesmen burying their heads in the sand and hoping for the best? The risk of Earth being hit by a comet or asteroid (collectively referred to as near Earth objects, or NEOs) large enough to cause regional or global devastation is real, not a Hollywood invention. It has happened many times in Earth’s history, most recently in 1908 when an NEO exploded over Siberia and leveled a huge swath of forest. Nonetheless, the false alarms propagated by the media over the threats posed by individual NEOs have frustrated astronomers. In response, they revised the Torino scale, which rates a NEO’s threat from 0 (no risk) to 10 (global catastrophe imminent) based on its size, speed, and probability of hitting Earth. Hazard level 1 used to be labeled “events meriting careful monitoring,” but is now labeled “normal.” NEOs that are initially rated 1 on the Torino scale are usually soon downgraded to 0. When an NEO is first discovered, astronomers can only roughly calculate its orbit. The calculation’s accuracy is improved by multiple observations of the NEO at different places along its trajectory. Many factors influence the motion of a NEO, including its mass, spin, the way it absorbs sunlight and radiates heat, and the gravitational pull of neighboring NEOs. 179
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When astronomers discovered asteroid 99942 Apophis in 2004, they estimated it had about a 3 percent chance of impacting Earth in 2029. That estimate has since been revised to 0, but a very small risk remains that during the close encounter in 2029, Earth’s gravity will put Apophis on track to impact Earth in 2036. NASA’s NEO survey program is working to identify and monitor the estimated 20,000 potentially hazardous NEOs greater than about 500 feet (140 meters) in diameter. None of the known objects has a Torino scale rating greater than 1 (see http://neo.jpl.nasa.gov/risk). The European Space Agency is currently planning an asteroid deflection test mission. The mission, Don Quijote, will consist of a spacecraft to impact an asteroid that is not a threat to Earth and an orbiter spacecraft to collect data. The main goal is to measure the deflection resulting from the impact and to use the data to perfect the technology.
Comet hangout What is the Oort cloud? The Oort cloud consists of rocks and icy debris left over from the formation of the planets. It envelops our solar system almost one light-year from the sun. Jan Oort, a Dutch astronomer, first hypothesized the cloud in 1950 to explain where new comets originate. The cloud, which has not been observed directly, may contain millions or even billions of dirty snowballs. Because they are only weakly held by the sun’s gravity, they can easily be deflected from their orbits and sent through the inner solar system, where astronomers observe them as comets.
Comet lifespan If comets leave behind a lot of dust or particles, won’t they disintegrate with time?
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Yes. When a comet ventures within about 500 million miles of the sun, some of its ice is converted into a gas, which escapes along with rock dust. A comet probably would lose most of its ice after a few hundred passes through the inner solar system. Even so, astronomers estimate that more than one trillion comets are “in reserve” in the Kuiper Belt, just beyond the orbit of Neptune, and in the Oort cloud at the frigid outer reaches of our solar system. Occasionally, one is shoved out of orbit and sent our way.
Messages from little green men? I’ve heard that scientists believe some rocks found in Antarctica came from Mars. What evidence do they have for this claim? Antarctica is a great place for finding meteorites because meteorites are easy to spot on the ice. Also, ice flows act as conveyor belts to concentrate the meteorites in certain regions. Ice with a cargo of meteorites, which may have fallen recently or a million years ago, piles up behind mountain barriers. Over time, wind erodes the ice and exposes the meteorites at the surface. Since the first meteorite find in Antarctica in 1912, about 25,000 meteorites have been recovered. Of these, only a very small number are from Mars. In fact, from finds all over the world, only 34 Martian meteorites have been identified. Three lines of evidence are used to determine which meteorites came from Mars: age, composition of trapped gases, and composition of the rock. Most putative meteorites from Mars are made of rocks that formed more recently (as little as 200 million years ago) than the rock of other meteorites. Scientists are not sure why only a few meteorite samples represent the older Martian rocks that constitute much of Mars. Whatever the reason, because all Martian meteorites are igneous—formed by volcanic activity—the rocks must have come from a body that still had volcanic activity at that time, which rules out asteroids or comets.
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NASA’s many Mars missions, including the Viking probes launched in the mid-1970s, have provided information about the geology and atmospheric composition of the red planet. The proportions of gases trapped in the meteorites (including nitrogen; carbon dioxide; and the rare gases neon, argon, krypton, and xenon) match those of the Martian atmosphere. Also, the ratio of hydrogen to deuterium—heavy hydrogen—in the meteorites is lower than that on Earth. Because Mars is only onetenth the mass of Earth, it cannot gravitationally retain the lighter hydrogen, which escapes and leaves behind the heavier deuterium. Finally, the chemistry of rocks suggests that they formed in the presence of more oxygen than we would expect to find on small bodies such as asteroids. Incidentally, the Martian meteorites tend to be shades of gray and black, similar to the igneous rocks just below the surface of Mars. Mars gets its red color from oxidized iron (rust) produced by the weathering of the surface rocks, and none of the meteorites is a weathered surface sample. One of the most famous rocks in the world is a Martian meteorite labeled ALH 84001, which was found in Allan Hills (ALH), Antarctica, in 1984. More than a decade ago, scientists found strange “fossillike” structures in the meteorite and claimed that it was evidence for life on Mars. Because nonbiological processes can produce similar structures, most scientists do not accept that the structures are evidence for life on the red planet.
Voyage into eternity I would like to see coffins sent into space. If other life exists out there, they may find the coffins. Can this be done? Hugo Gernsback, who is considered one of the fathers of science fiction, predicted that one day funerary spaceships would lift off on a regular basis with payloads of coffins headed for space burial. He imagined that the spaceships would be outfitted with deep freezers to store the coffins, conveyor belts to send the coffins to an expulsion tube, and a compression spring to shove the coffins into space. Download at www.wowebook.com
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Gernsback saw space burials as a solution to lack of land for cemeteries, and he thought that they would appeal to people who would rather remain frozen than decay in the ground. In 1956, he wrote that if man wants to be everlasting, he now has the chance. Of course, freeze-dried is a better description than everlasting. The prediction was optimistic. Sending coffins into space is technically possible, but it remains prohibitively expensive. If you want a space burial, you can have a lipstick-sized container with a small quantity of your ashes launched into space on a commercial rocket (Celestis Memorial Spaceflights). A canister containing the ashes will orbit Earth, eventually burning as it reenters the atmosphere. Some of the ashes of Star Trek creator Gene Roddenberry were “buried” this way.
From a distance How can astronomers measure the distance from Earth to far-away galaxies? They cannot use direct trigonometric functions. I was thinking of some variation of the Doppler effect, but this still seems unreasonable. At the beginning of the twentieth century, many astronomers thought that our own Milky Way galaxy comprised the entire universe. Astronomers had seen what we now know to be other galaxies, but without a way to determine how far away these objects were, they disputed whether they were “island universes” or components of the Milky Way. In 1924, Edwin Hubble (for whom the Hubble Space Telescope is named) settled this dispute by determining the distance to what is now known as the Andromeda Galaxy. Hubble calculated the distance using the inverse-square law, a mathematical formula that relates the apparent brightness of a light, its actual brightness, and the distance to the light source. To take an everyday example, if you know the actual brightness of a car’s headlights and measure the apparent brightness of the distant headlights, it is possible to calculate the distance to the car.
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Fortunately, astronomers have a good idea of the actual brightness of some objects in the universe, such as supernovae and Cepheid variable stars. Hubble used Cepheids, which are easily recognizable because they dim and brighten in a periodic way similar to a slow strobe light. Hubble showed that a Cepheid in the Andromeda Galaxy was too dim—and, therefore, too distant—to be within the Milky Way. For very distant galaxies, it is difficult to identify individual light sources, so astronomers must rely on other methods to estimate distance. One clue to a galaxy’s distance is its relative “lumpiness.” When observing nearby galaxies, it is possible to distinguish patches of dark and light, but the farther away a galaxy is, the smoother it looks because the stars blur together. Other methods use the Doppler effect. Just as the pitch of a siren is different depending on whether the siren is moving toward you or away from you, the spectrum of light from a galaxy varies depending on the motion of the galaxy. The Doppler shift in the spectrum of light reveals how fast a galaxy is rotating. Rotational speed reveals the actual brightness of the galaxy because it is related to a galaxy’s mass and the number of stars it contains. Doppler shift also shows how fast a galaxy is moving away from us. Hubble discovered that distant galaxies are receding more quickly than nearby galaxies. Therefore, astronomers can use Hubble’s law— the mathematical expression relating a galaxy’s distance and velocity—to determine the distance to a galaxy from the rate it is receding.
In the red How do scientists make such accurate estimates of the velocities of distant bodies using Doppler color shifts? Analogous to the decrease in the pitch of a siren as it moves away from us, light waves lengthen when a light source recedes. Light of longer wavelengths is closer to the red end of the spectrum, so this lengthening is referred to as a redshift. (For shifts in nonoptical wavelengths longer than red light, such as radio waves, the same term is used, although the shift is away from the red.)
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The Doppler redshift occurs when a nearby object moves through space away from Earth. In the case of distant objects that are receding because space itself is expanding, the effect is called a cosmological redshift. This distinction is not semantic. A different formula is required to calculate velocity from the cosmological redshift. The formula is based on general relativity and accounts for the stretching of space that occurs as the light beam is traveling. Astronomers often refer to the current location of a distant galaxy. They determine the galaxy’s distance by calculating how much space expanded during the time it took light to travel to Earth from the galaxy’s original position.
Revealing rays Please explain the term light-years. If the light from stars, galaxies, and planets takes such a long time to reach Earth, are those heavenly bodies still there in space in the same forms as when the light from them started traveling toward us? Did this light change in appearance during the time it was traveling? The term light-year often confuses people because it sounds like a unit of time, but is instead a measurement of distance. A light-year is the distance light—traveling at 300,000 km/s (186,000 miles per second)—travels in one year. One light-year equals approximately 6 trillion miles (nearly 10 trillion kilometers). We see heavenly bodies as they appeared sometime in the past. For instance, Proxima Centauri, our nearest star other than the sun, is more than 4 light-years away. We see Proxima Centauri as it was back when the light started traveling toward us, and any changes in the star would not be detectable for more than 4 years. As the light travels toward us, gases in space absorb specific colors of the light. These gases are found in the outer, cooler region of the star, in the space between stars, and in Earth’s atmosphere. Gases of different chemical elements absorb different colors. From the narrow bands of color that are absorbed—called spectral lines— astronomers can determine which chemical elements lie between the light source and us. Download at www.wowebook.com
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Hearing the beginning If the Hubble or an even more powerful telescope can eventually see the actual beginning of the universe at the time of the big bang, will that episode still be there? How can we tell if that particular spot deep in space is really the spot of origin? The big bang was not the same as an explosion of a bomb. It was an explosion of space itself that carried matter along with it. The big bang occurred everywhere at once; therefore, we cannot detect a spot of origin. We can detect, in every direction we look, the background radiation from the big bang, or at least from about 100,000 years after the big bang. Right after the big bang, the universe was a hot soup of elementary particles and energy so dense that light was continually reabsorbed. At the time when the universe had cooled enough for elementary particles to condense into atoms, electromagnetic radiation (light) became free to flow. This radiation, now lower in energy, is found throughout the universe. Scientists say that about 1 percent of the static picked up on a home radio or television antenna is caused by the background radiation from the big bang.
Zooming along How did we get so far from where the big bang took place that light from that area takes 15 billion years to reach us? Light from objects in the universe can take so long to reach us because, between the galaxies, space is expanding. (Note: We are not actually able to see light from the big bang itself.) When Einstein derived the mathematics of general relativity, the equations contained a scale factor that showed the universe was expanding. This possibility seemed so bizarre at the time that Einstein “fixed” the equations by introducing a mysterious force that
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would repel the force of expansion, a move he later called his “biggest blunder.” The expansion of three dimensions of space plus one dimension of time is difficult for us (even Einstein) to imagine from within our galaxy, which is not expanding. Kim Griest, a professor of astrophysics at the University of California, San Diego, explained that if you imagined the expansion going on inside a ball, the outer surface of the ball would not be expanding (our universe is not expanding into anything). Instead, within the ball, the scale factor is changing, analogous to the zoom function on a computer.
Star light, quasar bright I read that light from the earliest quasars can provide information about when the first stars formed. Heavy elements created in the furnaces of stars absorb certain wavelengths of light, and those wavelengths are missing from the quasar light when it reaches us. But if nothing can travel faster than light, how did elements that were created after the earliest quasars manage to get in a position to block the light? The light could have left the quasar when the universe was just a couple billion years old, and traveled for a few billion years before reaching a place between the quasar and us, where, in the meantime, stars had formed. The light, minus the wavelengths absorbed by the heavy elements from the stars, then traveled for several billion more years until it reached us. It takes light from quasars so long to get here because distant quasars are receding rapidly due to the expansion of space. To visualize why quasars are receding so fast, imagine raisins (objects in the universe) in bread dough (space between the objects). As the dough rises, the raisins get farther apart from each other. Raisins at opposite ends of the dough move away more quickly than adjacent raisins because more dough (space) exists between raisins that are separated by greater distance.
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Phantom force It is said that the more distant galaxies move away at greater speeds. Unless an unexplained force (such as an antigravitational force) exists, how is this possible? If the distance between adjacent raisins in rising bread dough increases by 1 inch, the distance between the first and third raisins would increase by 2 inches, 3 inches between the first and fourth raisins, and so on. So if space between objects is expanding at the same rate, more distant objects retreat more quickly than nearby objects. Additionally, evidence accumulating since the late 1990s suggests that the expansion of the universe is accelerating. Distant objects appear to be receding faster than Hubble’s law predicts. Assuming scientists’ understanding of gravity is accurate, their calculations indicate that a form of energy with a large negative pressure—an antigravity force—makes up 70 percent of the universe. Defining this “dark energy” remains one of the greatest mysteries in physics.
Middle universe If all galaxies are moving apart from one another, wouldn’t it be easy to pinpoint the center of the universe? Nearly all galaxies are indeed receding relative to each other. The exception is that within galaxy clusters—groups of galaxies held together by mutual gravitational attraction—galaxies move randomly with respect to one another. For example, the motions of the 40 or so galaxies within our local group are disordered, and the nearest major neighboring galaxy, Andromeda, is moving toward our Milky Way. Even ignoring the random motion of nearby galaxies, the recession of the galaxies does not make it possible to pinpoint the center of the universe because we can’t identify a position as the center of the expansion.
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On the one hand, the rate at which galaxies recede is proportional to their distance from us (Hubble’s law). More distant galaxies recede more quickly because more intervening, expanding space exists between us and distant galaxies than between us and less distant galaxies. However, this doesn’t say anything about our position relative to the center of the universe. Voyagers on the fictional Star Trek Enterprise, in a far away galaxy, could also look out to see other galaxies receding according to Hubble’s law.
Warp drive Is it possible that the expansion of space could allow us to journey to planets in distant galaxies without sitting in a rocket for years? For an intergalactic traveler, the expansion of space would be a hindrance instead of a help because it would keep increasing the distance to the destination. One might envision traveling at arbitrarily high velocities by shrinking space-time in front of a spaceship and expanding space-time behind the ship. The spaceship would surf along between the regions of shrinking and expanding space-time. By manipulating the fabric of space-time, the ship could arrive at its destination faster than a beam of light traveling the same distance without violating Einstein’s general relativity. This is because the ship itself would be confined to a bubble of space-time in which it did not travel faster than light in the local sense. How a warp drive or Alcubierre drive (named for Miguel Alcubierre, the physicist who proposed that it was theoretically possible) could expand and contract space-time is unknown. It’s complicated by the fact that the spaceship is cut off from the world outside the bubble. In addition, calculations show that the energy required to warp space is far greater than anything humanity can envision creating for the foreseeable future.
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Game of cosmic twister If the universe is circular in design, what would be beyond? In his book Bad Astronomy (Wiley, 2002), Philip Plait joked that cosmologists must get headaches trying to picture the curvature of space and the four dimensions, even if they refuse to admit it. Because we are stuck within our vast universe, similar to an ant in a gravel pit, it is tricky to size up the shape of space. Imagining that the universe is a big ball is appealing, but cosmologists tell us about three basic possibilities for the large-scale geometry of the universe. It could be flat or it could be curved. If it is curved, it could have a positive curvature—similar to the surface of a sphere (only in four dimensions instead of three)—or a negative curvature—similar to the surface of a saddle. A funky characteristic of a curved universe is that the shortest distance between two points is not a straight line. This is true of Earth’s surface. When flying between Europe and North America, the shortest distance is not a straight line—it is a great arc passing close to or over Greenland. If the universe is flat or has a negative curvature, it is infinite in extent. On the other hand, a universe with a positive curvature is finite in size. If the universe is finite, it does not mean that the stars and galaxies extend out to the edge, with empty space on the other side. Instead, space would bend back on itself. A spaceship that traversed the entire universe would return from the opposite direction, similar to a sailboat circumnavigating the globe. The idea that nothing, not even time or space, exists outside the universe is difficult to grasp because we are used to things having an inside and an outside. Plait argues that asking what is outside the universe is similar to asking what is north of the North Pole. For the analogy to work, we have to imagine that we are confined to the surface of Earth and cannot argue that the sky is north of the North Pole. Perhaps a more satisfying analogy is found in the work of the graphic artist M. C. Escher. Similar to the universe, Escher’s so-called “impossible structures,” including the looped staircase in “Ascending
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and Descending” and the topsy-turvy building in “Relativity,” defy our expectations about objects and geometry.
Extraterrestrials dig “The King” Is space really infinite? What else could be found even farther? According to Kim Griest, a professor of astrophysics at the University of California, San Diego, Einstein’s general theory of relativity does not tell us whether space is infinite. Space could be either infinite or finite but curved back on itself. Measurements suggest that the universe is flat and, therefore, infinite. Yet for the same reason people were once fooled into thinking Earth was flat, these measurements could be misleading. The universe could be curved but so large that any small part of it appears flat. What is beyond our universe is a mystery. In fact, Griest points out that we cannot even see the entire universe. The light has not had time to get here, although each year we can see one light-year (6 trillion miles) farther. The rest of the universe probably looks similar to the parts we can see already, but beyond the universe, speculation ranges from “the universe is everything,” to “an infinite number of parallel universes could exist.” Proponents of parallel universes say that these other universes could have completely different laws of physics or could differ just subtly from our own universe. For example, Elvis might still be alive in some universe. Unfortunately for Elvis fans hoping to attend a concert that is out of this world, we have no way to access these other worlds, even if they exist.
The stork brought it I’ve heard of the big bang. What current theories are scientists proposing for the beginning of the universe?
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The big bang—the origin of space and time in a huge explosion— is the most well-accepted theory of how the universe came to be. The first evidence in support of the theory was Edwin Hubble’s discovery in 1929 that the universe is expanding. Big bang theory has always had critics. Certain aspects of the theory, such as the nature of the mysterious dark energy and dark matter inferred to make the theory fit observation, remain poorly understood. In the 1940s, scientists who were troubled by the apparent breakdown of the laws of physics at the instant of the big bang proposed steady-state theory. According to steady-state theory, stars and galaxies may change, but overall the universe has always been as it is now. As the universe expands, new matter is being created continually in the voids of space, so the density of the universe is unchanging. Ironically, work done by proponents of steady-state theory provided the second piece of evidence in favor of big bang theory. The amount of light elements in the universe (such as helium, deuterium, and lithium) exceeds what scientists’ calculations indicate the stars could have produced. Most scientists accept that these elements were produced in the intensely hot conditions of the big bang. Physicist Stephen Hawking said the discovery in 1965 of what is thought to be microwave radiation left over from the big bang was the final nail in the coffin of steady-state theory. However, proponents of a revised, quasi-steady-state theory explain this radiation as diffuse starlight that objects in space have continually absorbed and emitted. Another rival of big bang theory, plasma universe theory, proposes that the universe has been around forever and that it began as a uniform plasma. Plasma is a hot gas in which electrons have become separated from atoms. Plasma makes up much of the universe. The strongest support for plasma universe theory comes from laboratory experiments using electromagnetic fields, which have been able to replicate (on a small scale) the patterns of plasma seen in galaxies. Recently proposed membrane theory, an extension of string theory, views our visible four-dimensional (three dimensions of space and one of time) universe as confined to a hypersurface, or sort of membrane, that is embedded in 11-dimensional space. It postulates that our universe and other universes were created by a collision between membranes. The expansion of our universe was triggered by energy released
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in the collision. It may sound like science fiction, but it arose from physicists’ mathematical models. Membrane theory explains one of the greatest mysteries of the universe: why the strength of gravity is much smaller than that of the other fundamental forces—the electromagnetic force and the strong and weak nuclear forces. Gravity is weaker because it “leaks” into the other dimensions, and the other fundamental forces stay within the membrane to which our universe is confined.
Tock tick In “alternate universe” theory, do all universes move forward in the same unit of time? The prediction that multiple, parallel universes coexist arises from the complex mathematics of string theory. By modeling subatomic particles as vibrations of tiny strings, string theory is able to unite quantum theory with general relativity, thereby bridging a gap that has long troubled physicists. The concept of alternate universes seems pretty bizarre. But even weirder, some physicists believe that an infinite number of universes could exist, each with different properties. Some might not have any atoms or stable matter of any kind. Some might be nearly identical to our universe. Time could progress differently in these other universes; but if you are hoping we could travel back and forth in time by flitting between universes, no such luck. According to Michio Kaku in his book Physics of the Impossible (Anchor, 2008), accessing other universes is not forbidden by the laws of physics, but it would require a vast amount of energy and technology considerably more advanced than our own.
Galileo’s legacy If the universe is expanding at greater than the speed of light, does that mean that no matter how strong we make our telescopes, we will always be losing ground?
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What a telescope detects does indeed depend on how far light must travel to reach it. Telescopes are sometimes referred to as time machines, but a telescope simply collects the starlight that strikes the whole surface of its lens or mirrors, and concentrates the light into a narrow beam. Yet telescopes do look back in time. In fact, our eyes can, too. The sunlight peeking through the window left the sun more than 8 minutes ago. The light from the nearest star system, Alpha Centauri, takes 4.4 years to reach us. Light from the most distant galaxies has traveled through space for billions of years. Stronger telescopes can look further back in time because they can detect fainter, more distant stars and galaxies. With the best technology currently available and the help of nature’s gravitational telescopes—large clusters of galaxies that bend and amplify the light from more distant objects—it is possible to detect galaxies that existed more than 13 billion years ago. The next generation of behemoth telescopes currently in the works, including the Giant Magellan Telescope, the Thirty Meter Telescope, and the European Extremely Large Telescope, may be able to see a little further back in time, but not much. The universe is 13.7 billion years old, and the lights did not go on in the universe until the first stars formed a few hundred million years after the big bang. The new telescopes will help astronomers see finer details. For example, what previously looked like a fuzzy blob may turn out to be a beautiful spiral galaxy. Without these kinds of details, astronomers cannot determine how the first galaxies formed or understand what the conditions were like as they were forming. The cosmological horizon—a boundary in time that marks the limits of the observable universe—is equal to the age of the universe. With each passing second, the cosmological horizon moves outward, as light from increasingly distant sources has more time to travel to us. Yet, the universe is expanding, and the objects most distant from us are receding at greater than the speed of light. As a result, distant objects are racing out of our field of view, and the knowable universe does not include all the space and matter that emerged in the big bang.
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Einstein didn’t lie In a column, you asserted, “[O]bjects most distant from us are receding at greater than the speed of light.” Doesn’t this contradict Einstein’s theory of special relativity that no information or material object can travel faster than the speed of light? Albert Einstein did indeed conclude that it is impossible to travel faster than light. But his theory of special relativity applies only to motion through space. Distant galaxies are not zooming through space. They are receding from us (or us from them, depending on one’s perspective) because space itself is expanding.
Light light I have read that many subatomic particles are weightless. If this is true, why can’t light escape from black holes? Most subatomic particles—including the electrons, protons, and neutrons that make up the atom, and the quarks that constitute the protons and neutrons—do have a mass. It is true that photons—particles of light—have a zero-rest mass. Photons are always traveling at the speed of light, so they have energy and momentum, which is why they can “push” a solar sail, for example. To understand why gravity can bend light, we need to exchange Isaac Newton’s theory, which fails if extremely high speeds or very strong gravity are involved, with Albert Einstein’s. Newtonian mechanics treats gravity as a force, envisions space as perfectly uniform, and does not predict that gravity would bend light rays because light has no mass. Nevertheless, one of the first confirmations of Einstein’s general theory of relativity was that light from the stars was bent as it passed close to the sun. According to Einstein, gravity is caused by the curvature of space. A massive object, such as the sun or a black hole, distorts the space
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around it. One way to think about it—although keep in mind that Einstein’s theory involves the more complex geometry of fourdimensional space-time—is to imagine a heavy stone (a black hole) in the middle of a mattress (space). A ball of any size (light) placed on the mattress in the vicinity of the rock will follow a curved path near the well created by the rock. Because a black hole is so massive, the distortion of space around it is extreme. Therefore, light traveling very close to the black hole can become trapped in the black hole’s gravity well.
Want stars with that? If black holes gobble everything in their surroundings, wouldn’t the whole universe end up in one big black hole? We would be in trouble if black holes behaved like great cosmic vacuum cleaners. As far as astronomers can tell, our galaxy contains several black holes. Most weigh only about 8 to 15 times the mass of the sun. A supermassive black hole, weighing about 3 million solar masses, appears to lie at the center of the Milky Way. As the name suggests, we cannot exactly see black holes, but other evidence confirms their existence. Astronomers have detected what they believe to be radiation produced as violent collisions heat matter that is plunging into a black hole. They have also detected stars behaving as though they are orbiting a massive invisible object. Just as Earth and the other planets in the solar system orbit the sun without being sucked in by its gravity, it is possible for an object to orbit a black hole without being gobbled up. At a distance, the gravitational field of a black hole is the same as that produced by any object of the same mass. Closer to a black hole, things are different because space is greatly warped. Within a certain distance from a black hole—the Schwarzchild radius—an object would be doomed because it would have to move at more than the speed of light to escape. The warping of space would also make escape difficult within a few Schwarzchild
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radii from a black hole. For the smaller black holes in the Milky Way, this is about 100 miles (160 km). For the supermassive black hole at the center of the galaxy, this is the equivalent of about one-tenth the average distance of Earth from the sun.
Supersize I read that 50 billion times the mass of the sun is the maximum estimated size to which a black hole can grow. Why can’t a black hole grow any larger? Why did anyone need to know this number? The estimate that black holes can grow to only a few tens of billions of times the mass of the sun comes from a computational model of the evolution of the universe. The model predicted more ultramassive black holes than are actually evident. If the model is accurate and growth of black holes is indeed physically limited, it may be because, as black holes consume their surroundings, they eventually radiate so much energy that they interrupt the gas supply that feeds them. Most galaxies, including our own, are thought to contain central black holes. The sizes of the black holes and the masses of the galaxies seem to be in step. Therefore, understanding the growth of black holes is critical to understanding how galaxies form and evolve.
Cute little—ahhhhh! If, as some people fear, the new European Organization for Nuclear Research (CERN) collider creates a black hole that eats Earth, does anyone know how long it would take for Earth to be devoured? The Large Hadron Collider (LHC) at CERN, near Geneva, could be powerful enough to create a mini black hole (smaller than an atomic nucleus), but only if the universe contains hidden dimensions. By propagating into these dimensions, gravity’s strength would increase. As a result, a particle would not need to be packed into quite as small a region to become a black hole. Download at www.wowebook.com
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Physicists are enthused about the possibility of producing mini black holes because it would be proof that hidden dimensions of space exist in reality, not just in the funky mathematical calculations of string theory. Mini black holes should evaporate instantaneously, according to Stephen Hawking’s prediction that black holes radiate energy at a rate inversely proportional to their size. The particles emitted by an evaporating black hole could reveal how many extra dimensions of space exist. If Hawking is wrong, worst-case scenario calculations suggest that it would take at least thousands of years for a mini black hole to eat Earth atom by atom. Fortunately, we don’t have to rely only on calculations to show that any mini black holes produced in the LHC would be safe. Higher-energy collisions already occur when cosmic rays hit our atmosphere. So if a particle accelerator can produce mini black holes beneath our feet, nature is already producing them above our heads.
Wimp? Says who? If six times more dark matter exists than baryonic matter, and the only way it interacts with real matter is gravitationally, what happens when dark matter falls into a black hole? Also, do the stars and planets have dark matter? As far as the experts can tell, the universe does have about six times more dark matter than visible matter. Some of the dark matter is baryonic—matter made of ordinary atoms. For example, planets, dead stars, and black holes account for some dark matter. These large objects that do not emit light are known collectively as MACHOs (massive compact halo objects). The work of Kim Griest, a professor of astrophysics at the University of California, San Diego, and others have shown that the bulk of dark matter is not MACHOs. The identity of the non-MACHO dark matter is one of the greatest mysteries in physics. One possible candidate is WIMPs (weakly interacting massive particles).
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No one has actually detected a WIMP, but the number crunching of theoretical physicists predicts the existence of these particles. The big bang would have created WIMPs that spread throughout the universe. Despite the M standing for massive in both WIMPs and MACHOs, WIMPs are tiny—probably about 200 times heavier than a hydrogen atom. But that is huge compared to other elementary particles. WIMPs do not interact through the strong nuclear force, the “glue” that holds atoms together. Therefore, unlike normal atoms, they are elementary— they do not consist of smaller particles such as protons and electrons. Most of the dark matter is spread between the stars where most of the space is, but the stars and planets may have dark matter, too. If WIMPs exist, they have probably been passing through the stars and planets for billions of years. Occasionally, WIMPs may collide with atoms in these objects, lose energy, and be captured by their gravity. Because they interact weakly with matter, it is possible that the WIMPs spiral down and collect at the center of Earth and the sun. WIMPs could fall into a black hole because they can interact through the force of gravity. Their mass would be added to that of the black hole. Griest explained that because WIMPs are elementary particles, they would not be ripped apart like ordinary matter; they would be squashed into oblivion at the black hole’s center.
Solar system synchrony Do all the planets of our solar system and the sun rotate in the same direction? Do they all rotate left or right, or is there variation in direction? If so, why? All the planets in our solar system revolve around the sun in the same direction as the sun rotates on its axis: counterclockwise, as seen from above Earth’s North Pole. Most of the planets also rotate counterclockwise on their axes. The exceptions are Venus, Uranus, and the recently demoted dwarf planet Pluto, which rotate clockwise.
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The planets orbit in the plane of the sun’s equator—the ecliptic plane. Mercury and Pluto deviate slightly. The plane of Mercury’s orbit lies at 7° and Pluto’s lies at 17° relative to the ecliptic plane. The flatness of the solar system and the fact that the sun’s spin and planets’ revolutions are in the same direction is taken as evidence that the sun and the planets originated from a single cloud of dust and gas. About 4.6 billion years ago, the cloud began contracting under the influence of its own gravity, likely stimulated by a cataclysmic event such as the explosion of a nearby star or a collision with another dust cloud. Similar to the effect of skaters pulling in their arms, the contraction of the cloud caused it to spin faster. During collapse, clumps of gas within the cloud collided and merged, with the new clumps having the average velocity of the original clumps. Therefore, motions became more orderly and the cloud flattened into a disk. The resulting swirling disk—the solar nebula—had a dense, hot center that became the sun. The planets formed in the outer part of the disk. They began as grains of dust that functioned as tiny platforms on which other atoms could accumulate. The shape and rotation of the solar nebula left its mark on the solar system. Astronomers speculate that anomalies, such as the backward rotations of Venus and Uranus, resulted from collisions between large bodies during the formation of the solar system. The great amount of order in the solar system was not completely obvious to ancient astronomers. In fact, the Greek root of the word planet means “wanderer,” and early models of the solar system gave the planets complex paths. From a vantage point on Earth, the planets seem to speed up, slow down, and even loop back and forth relative to the stars. Now we know that the apparent wanderings of the planets occur because Earth is moving relative to them. For example, Mars appears to slip backward as Earth overtakes it in its orbit around the sun.
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Analogy anomaly Why do (almost) all the planets orbit the sun on the same plane? I’ve seen numerous examples showing the trampoline and the bowling ball, but the reference suggests a two-dimensional plane. If the “bowling ball” were to weigh down space-time, wouldn’t it affect the entire area around the object and result in planetary orbits on numerous planes? The textbook example of the bowling ball distorting a twodimensional rubber sheet is not intended to show why the planets orbit the sun on the same plane. It is an analogy for Einstein’s explanation of gravity. Matter distorts the fabric of four-dimensional space-time similar to the way a heavy ball distorts a two-dimensional rubber sheet. The analogy is simplistic, and the planets could indeed orbit the sun on different planes. Instead, they are on the same plane because of the way the solar system formed. It formed from a spinning disk of gas and dust, and the planets’ orbits largely remained within the plane of the disk from which they were born.
Death by fire Why do stars die? What makes them die? The death of stars is a multistep process that gives rise to some of the most amazing objects in the universe. Knowledge about this process comes from a combination of theoretical modeling and observations of stars that are at different stages of their life cycles. A star’s life is an extended battle between two forces: the inward crush of gravity and the outward thrust of thermal pressure. Stars
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start out fusing hydrogen into helium in their cores, a process that generates tremendous heat and pressure and counterbalances gravity. When nuclear fusion slows as the hydrogen in the star’s core is depleted, gravity begins to shrink the star. As the star squeezes inward, it heats up. This initiates hydrogen fusion in a layer around the core, which was not previously hot enough to sustain fusion. Hydrogen fusion proceeds so rapidly in this layer that the thermal pressure pushes the star’s upper layers outward. The star gradually becomes a very large, luminous star called a red giant. Meanwhile, helium continues to be added to the star’s contracting core. Eventually, except in the smallest stars, the core temperature gets high enough to sustain the fusion of helium into carbon. A small star’s death is imminent when core helium is converted into carbon because core temperatures will not get high enough to sustain carbon fusion. Until the carbon core cools down, it emits ultraviolet radiation, which causes the gas in the star’s expanding outer layers to glow brightly. These beautiful, glowing shells of gas are referred to as planetary nebulae because, seen through small telescopes, they resemble planets. Powerful modern telescopes, such as the Hubble, reveal the intricate details that inspire names such as Cat’s Eye Nebula and Spirograph Nebula (see http://hubblesite.org/). In a high-mass star, the core temperature gets high enough to sustain carbon fusion and then fusion of progressively heavier elements. Iron ultimately piles up in the star’s core—a dead end because iron cannot generate energy from fusion. Unopposed by the thermal pressure from fusion, the tremendous crush of gravity forces protons and electrons in the core to combine to form new particles—neutrons and neutrinos. The core collapses, generating a violent shock wave, which drives off the outer layers of the star and produces a brilliant supernova. The core ball of neutrons that remains is called a neutron star. It is so dense that a teaspoonful would weigh about a billion tons. If the core’s remaining mass is large enough, it can collapse to form a black hole.
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The end—not! I understand that Earth and the sun will align with the center of the Milky Way on December 21, 2012. What effect, if any, will this have on Earth? The Internet hosts a plethora of funky claims about this, with various interpretations of what it means to align with the center of the Milky Way. Some claims imply that our solar system will pass through the center of the Milky Way, which would have effects. At the center of the galaxy, the density of stars is a million times greater than in our solar neighborhood. That is close enough for collisions between stars to be a risk. The galactic center is also thought to contain a black hole, but it would swallow us only if we got very close. However, our solar system is in the suburbs of our galaxy, more than 26,000 light-years from the center of the Milky Way. We are situated in the galactic disk, which is 100,000 light-years across. We slowly circle the galaxy center, but we do not approach it.
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Index A abiogenic theory of oil formation, 135 absolute zero, 89 Acasta Gneiss, 144 adhesive mucus in snails, 32-33 age, determining age of Chicxulub crater, 136-137 age of Earth, 144-145 carbon dating, 143-144 Alcubierre drive, 189 Alcubierre, Miquel, 189 ALH 84001 meteorite, 182 alignment with center of Milky Way on December 21, 2012, 203 alive, definition of, 72 Allee effect, 46 aluminum recycling, 111 Andromeda Galaxy, 183 Anopheles mosquitoes, 2 anthocyanins, 59-60, 65 antipodes, 91 ants Argentine ants, 12-13 birds nesting close to, 19
breathing process of, 14-15 communication among, 12 eradicating from homes, 12-13 apposition compound eyes, 15 Argentine ants, 12-13 Aristotle, 172 arthropods. See spiders, 1-5 asteroids asteroid deflection, 180 risk of Earth being hit by asteroid, 179-180 astronomical seasons, 162-163 atoms electrons, 95 forces between, 96 motion in, 88-89 auditory system, sensitivity of, 89 average regional and global temperatures, 121-122
B background radiation from big bang, 186 bacteria, Pasteurella multocida, 41 Bad Astronomy (Plait), 190
205
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bags, paper versus plastic, 112-114 Baldocchi, Dennis, 72 banner clouds, 168 bats, echolocation of, 31 bees birds nesting close to, 19 Colony Collapse Disorder (CCD), 17-18 life span of, 16 resource competition with birds, 18-19 visual adaptations for foraging in dim light, 15-16 behavioral constraints and extinction, 46-47 betalains, 65-66 big bang, 186-187, 192-193 bioluminescence in fireflies, 20 biosolids, 115 birds condors, 37-38 echolocation, 31 flocking behavior, 26-28 hummingbirds avoidance of obstacles during flight, 30-31 FFF (flicker fusion frequency), 31 metabolic rate, 31 optokinetic response, 31 resource competition with bees, 18-19 Passenger Pigeon, 46 species nesting close to bees, wasps, and ants, 19 black holes light trapped in, 195-196 maximum size of, 197
bags
mini black holes, 198 warping of space near, 196-197 bleaching of coral, 68-69 of hair in sunlight, 81-82 Bock, Yehuda, 142 boiling water, adding salt to, 75-76 borders, effect of geological changes on, 141-142 Bradbury, Ray, 79, 115 brains of insects, 9-10 similarities between human/animal thinking, 51-52 breathing in ants, 14-15 Bt, insecticide, 68 bubbles, shape of, 81 buoyancy of humans, 49-50 burning of fossil fuels, impact on oxygen concentration, 122-123 butterfly migration and navigation, 7-8
C calculating distance to horizon, 166-167 distance to other galaxies, 183-184 mass of Earth, 147-148 speed of light, 92 velocities of distant objects, 184-185 weight of Earth, 145-148 calendars Calendrier positiviste, 161 Celtic calendar, 162 Gregorian calendar, 159-161 Islamic calendar, 161
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Columbus, Christopher
Jewish calendar, 161 Julian calendar, 159-161 lunar calendars, 161 lunisolar calendars, 161 Calendrier positiviste, 161 California San Andreas Fault system, 143 California Spatial Reference Center (CSRC), 142 camels, water conservation and dehydration tolerance, 24-26 carbon dating, 143-144 carbon dioxide (CO2), increase from greenhouse gas emissions, 123-126 carbon-12, 143-144 carbon-14, 143-144 Caribbean plate movement, 140-141 carotenoids, 65-66 carpenter’s level, 148 cats domestication and breeding of, 38-39 Felis silvestris lybica, 38 CCD (Colony Collapse Disorder), 17-18 Celtic calendar, 162 Cepheids, 184 CERN (European Organization for Nuclear Research), 197 Chicxulub crater, 136-137 China, Three Gorges Dam, 146 chirping of crickets, 21 Chitty, Dennis, 48 chorus-line hypothesis, 28 chromatophores, 50 circadian rhythm, 4
207
climate change, 118 average temperature measurements, 121-122 changes in oxygen concentration due to burning of fossil fuels, 122-123 effect on number and intensity of hurricanes, 99 greenhouse gas emissions, 123-126 impact on precipitation, 108-109 increase in sea water temperature, 68-69 solar cycles and, 120 clothing, recycling, 110-111 clouds, 168 clover, four-leafed, 66 CO2 (carbon dioxide), increase from greenhouse gas emissions, 123-126 coal coal fires, 134-135 formation of, 135 Coats for Cubs (HSUS program), 111 cohesion-tension theory, 60-61 cold-water coral species, 69-70 Colony Collapse Disorder (CCD), 17-18 color color changes in animals, 50-51 color fading in sunlight, 81 in wet fabric, 80 of rainbows, 164-165 of sky, 169 Columbus, Christopher, 152-153
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208
comets lifespan of, 181 Oort cloud, 180 risk of Earth being hit by comet, 179-180 Committee of Inquiry into Calendar Reform, 161 communication among ants, 12 Comte, Auguste, 161 condors, 37-38 conduction of heat, 82-83 conjunctiva, 39 cooling houses, 87 coral bleaching, 68-69 cold-water coral species, 69-70 increasing sea water temperatures and, 68 rising sea levels and, 68-69 Coriolis effect, 104-107 corn development of, 67 genetic engineering, 67 coronae, 163-164 corrosion, 79-80 crickets, chirping of, 21 CSRC (California Spatial Reference Center), 142 curvature of Earth, 149 of universe, 190-191 cyclones, naming conventions for, 100
D dark energy, 188 dark matter, 198-199 Darwin, Charles, 53
comets
dating age of Chicxulub crater, 136-137 age of Earth, 144-145 carbon dating, 143-144 death of stars, 201-202 dehydration tolerance of lichens, 56 delphinidin, 64 dendrochronology, 144 deoxyribonucleic acid. See DNA desert mirages, 163 deuterium, 176 diamonds, 76-77 distance, calculating to horizon, 166-167 to other galaxies, 183-184 DNA (deoxyribonucleic acid) genetic overlap between species, 44-46 of insects, 8-9 Do Lemmings Commit Suicide?: Beautiful Hypotheses and Ugly Facts (Chitty), 48 dodder, 55 dog days of summer, 158 dogs allowing dogs to lick wounds, 40-41 domestication and breeding of, 38-39 saliva, 40-41 tear stains, 39-40 dolphins, sleep in, 34-35 Doppler effect, 184-185 double sun mirages, 156 drain swirl, direction of, 105-107
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expansion of universe
dromedaries, water conservation and dehydration tolerance, 24-26 droughts, 107-108 dusk, color of sky at, 169
E E = mc2, 148 Earth age of, 144-145 alignment with center of Milky Way on December 21, 2012, 203 curvature of, 149 distance to other galaxies, 183-184 effect of moon on, 177-178 magnetic field, 150-152 mass of, 147-148 polarity reversals, 151-152 tilt on axis, 150 weight of, 145-148 wobble on axis, 150 earthquakes, 132 earthquake-induced wobble and change in day length, 139-140 geological changes and country borders, 141-142 long-range effects of, 140 Love waves, 138 magnitude, 137 Modified Mercalli Intensity Scale, 138 and movement of Caribbean plate, 140-141 primary waves, 138 Rayleigh waves, 138 Richter scale, 137 secondary waves, 138
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ecdysone, 8 echolocation, 31 eggs, green color in hard-boiled egg yolks, 75 Einstein, Albert, 93, 186, 195 El Niño, 108-109 El Niño–Southern Oscillation (ENSO), 109 electricity, static, 90-91 electrons, 95 elephants, reputed fear of mice, 26 Elysia chlorotica, 54 Encyclopedia of Natural History (Pliny the Elder), 26 Endangered Species Act (ESA), 44 energy consumption nuclear waste disposal, 126-127 of lights, 116 of TVs, 115-116 Enriquillo–Plantain Garden Fault, 140 ENSO (El Niño–Southern Oscillation), 109 Environmental Protection Agency Indoor Air Quality Information Clearinghouse, 71 epiphragm, 33 equinoxes, 162-163 eruptions of volcanoes, 132-134 ESA (Endangered Species Act), 44 ethylene, 58-59 European Organization for Nuclear Research (CERN), 197 European Space Agency, 180 expansion of universe, 186-189, 195
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210
extinction, behavioral constraints and, 46-47 eye of hurricanes, 99 eyes apposition compound eyes, 15 conjunctiva, 39 superposition compound eyes, 15 eyewall of hurricanes, 99
F fabric color changes in wet fabric, 80 recycling, 110-111 fading in sunlight, 81 Fahrenheit 451 (Bradbury), 115 fata morgana, 164 Felis silvestris lybica, 38 Festival of the Departing Sun, 162 FFF (flicker fusion frequency), 29-31 fire of diamonds, 77 fireflies, 20-21 fires, coal, 134-135 fish adaptations to cold, 36-37 color changes in, 50 largest species of freshwater fish, 35 swimbladder, 49 flicker fusion frequency (FFF), 29-31 flies flight boundary layer, 6 life span of, 5 pain detection by, 11 sleep in, 4 flight boundary layer (insects), 6 flocking behavior of birds, 26-28 flower pigmentation, 63-66
extinction
fogbows, 163-164 forces between particles, 96 fossil fuels coal fires, 134-135 formation of, 135 impact on oxygen concentration, 122-123 four-leafed clover, 66 freeway noise, 89-90 freezing water frost formation, 86-87 icicles on ice cubes, 85 Mpemba effect, 84-85 rapid freezing phenomenon, 85-86 freshwater fish, 35 frost, 86-87 fruit flies pain detection by, 11 sleep in, 4 fruits living nature of, 72-73 ripening process, 58-59 seedless fruits, 57-58 fungi lichens, 56 mold in homes, 70-71 furs, recycling, 111
G galaxies, measuring distance to, 183-184 gemstones diamonds fire, 77 refractive index, 76-77 irradiated gemstones, 78-79 general theory of relativity, 195 genetic diversity, 37-38
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Humane Society
genetic overlap between species, 44-46 genetically modified plants ecological and health risks, 67-68 roses, 64 geodynamo, 150 geological changes and country borders, 141-142 geometry of universe, 190-191 Gernsback, Hugo, 182-183 gibbous phase of moon, 173-174 glacial/interglacial cycles, 117-120 glass recycling, 112 global climate change, 118 average temperature measurements, 121-122 changes in oxygen concentration due to burning of fossil fuels, 122-123 effect on number and intensity of hurricanes, 99 greenhouse gas emissions, 123-126 impact on precipitation, 108-109 rising sea levels, 68-69 solar cycles and, 120 global temperatures, 121-122 gluons, 96 GRACE (Gravity Recovery And Climate Experiment), 146-147 gravity, 94, 146-147, 195 Great Lakes tides, 131 green color in hard-boiled egg yolks, 75 green flash, 170 green sea slug (Elysia chlorotica), 54
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greenhouse gas emissions, 116-117, 123-126 Gregorian calendar, 159-161 Gregory XIII, 159 Griest, Kim, 187, 191, 198 Groundhog Day, 163 gyres, 113
H Hadley Circulation, 104 hair, bleaching by sun, 81-82 hard-boiled eggs, green color in yolk, 75 Hawking, Stephen, 192, 198 heat defined, 88-89 thermal conductivity, 82-83 helium-3, 175-176 helium-4, 176 hemimetabolous insects, 9 hemiparasites, 55 hemolymph, 14 highway mirages, 163 History of the Life and Voyages of Christopher Columbus (Irving), 153 hoar frost, 87 holometabolous insects, 9 holoparasites, 55 Holway, David, 13 honeybees. See bees, 15-19 horizon calculating distance to, 166-167 enlarged appearance of moon near horizon, 172-173 houses, cooling, 87 Hubble, Edwin, 183 Humane Society of the United States (HSUS), Coats for Cubs program, 111
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212
humans buoyancy, 49-50 pain detection by, 11 similarities between human/animal thinking, 51-52 hummingbirds avoidance of obstacles during flight, 30-31 FFF (flicker fusion frequency), 31 metabolic rate, 31 optokinetic response, 31 resource competition with bees, 18-19 hurricanes development of, 98-99 eye, 99 eyewall, 99 global warming and, 99 strength of, 98 weakening or rerouting, 97-98 hybrid sterility, 42-43 hypothetical hole through center of Earth, 91-92
I ice ages glacial/interglacial cycles, 117-120 Little Ice Age, 118-119 ice cubes, icicles on, 85 images of moon landing sites, 174-175 inferior mirages, 163 infinity of universe, 191 infrared (IR) signals, 88 insecticides, Bt, 68
humans
insects ants Argentine ants, 12-13 birds nesting close to, 19 breathing process of, 14-15 communication among, 12 eradicating from homes, 12-13 bees birds nesting close to, 19 Colony Collapse Disorder (CCD), 17-18 life span of, 16 resource competition with birds, 18-19 visual adaptations for foraging in dim light, 15-16 brains, 9-10 crickets, chirping of, 21 DNA profiles, 8-9 flies fireflies, 20-21 fruit flies, 4, 11 life span of, 5 flight boundary layer, 6 hemimetabolous insects, 9 holometabolous insects, 9 metamorphosis, 8-9 monarch butterfly migration and navigation, 7-8 mosquitoes Anopheles mosquitoes, 2 consumption by spiders, 1-2 pain detection by, 10-11 interglacial periods, 117, 120 International Astronomical Union, 171
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Mapping Time (Richards)
ionizing radiation, 78 IR (infrared) signals, 88 iron corrosion, 79-80 iron sulfide, 75 irradiated gemstones, 78-79 Irving, Washington, 153 Islamic calendar, 161
J jet stream, 103-104 Jewish calendar, 161 Joint Typhoon Warning Center, 100 Julian calendar, 159-161
K Kaku, Michio, 193 kangaroos, pouch hygiene of, 32 Knowlton, Nancy, 69 Kuiper Belt, 181
L lakes, Great Lakes tides, 131 lampyrids, 20 Large Hadron Collider (LHC), 197 leap years, 160 leaves, movement in wind, 71-72 lemmings, 47-48 length contraction, 94 lenticulars, 168 Lentiformis mesencephali (LM), 31 LHC (Large Hadron Collider), 197 lichens, 56
213
life, definition of, 72 life span of bees, 16 of comets, 181 of flies, 5 light black holes and, 195-196 light from quasars, 187 speed of light, 195 calculating, 92 upper limit on speeds, 92-93 light-years, 185 lightning bug fireflies, 20 lights, electric energy consumption, 116 greenhouse gases emitted by porch lights, 116-117 switching on/off, 116 Little Ice Age, 118-119 lizards color changes in, 50 “pushups” and head bobbing, 23-24 LM (Lentiformis mesencephali), 31 Love waves (earthquakes), 138 luciferin, 20 lunar calendars, 161 Lunar Reconnaissance Orbiter, 175 lunisolar calendars, 161
M MACHOs (massive compact halo objects), 198 magnetic field of Earth, 150-152 magnitude of earthquakes, 137 Mapping Time: The Calendar and Its History (Richards), 161
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214
Mariana Trench, 130 Mars, meteorites from, 181-182 marsupials, pouch hygiene, 32 mass of Earth, 147-148 massive compact halo objects (MACHOs), 198 Mayr, Ernst, 43 meibomian glands, 40 meiosis, 42 Mekong giant catfish, 35 melanin, 81 membrane theory, 192 mesocyclones, 101 metabolic rate of hummingbirds, 31 metal corrosion, 79-80 metamorphosis of insects, 8-9 meteorites, 181-182 meteorological seasons versus astronomical seasons, 162-163 mice, elephants and, 26 migration in monarch butterflies, 7-8 mini black holes, 198 mirages, 163-164 mistletoe, 55 Modified Mercalli Intensity Scale, 138 mold in homes, 70-71 molocules, electric charges of, 90-91 moment magnitude of earthquakes, 137 monarch butterfly migration and navigation, 7-8 moon effect on Earth, 177-178 enlarged appearance near horizon, 172-173 gibbous phase, 173-174
Mariana Trench
helium-3 on, 175-176 moon landing sites, 174-175 name of, 171 rotation and revolution, 171-172 mosquitoes Anopheles mosquitoes, 2 consumption by spiders, 1-2 Mount Pinatubo, 133 Mount St. Helens, Washington, 133 Mpemba effect, 84-85 Mpemba, Erasto, 84 mucus in snails, 32-33 mules, 42 Murphy, Tom, 147 mushroom bodies of insect brains, 10 The Mystery of the Moon Illusion (Ross and Plug), 172
N naming cyclones, 100 moons, 171 tropical depressions, 100 near Earth objects (NEOs), 179-180 neurobiology of plants, 54 neutrons, 95 Newton’s law of gravitation, 94 nociceptors, 11 Nosema ceranae, 17 Nuclear Regulatory Commission (NRC), 79 nuclear waste disposal, 126-127 nucleus of atoms, 95 nudibranches, 51
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plastic
O oceans formation of new oceans, 129-130 gyres, 113 maximum depth, 130 Southern Ocean, 129 oil, formation of, 135 Olividae, 33-34 Oort cloud, 180 optic lobes of insect brains, 10 optokinetic response, 31 orbit of planets, 201 orographic lift, 168 oxygen concentration and burning of fossil fuels, 122-123
P P waves (earthquakes), 138 Pacific Northwest, precipitation in, 102 Pacific Plate movement, 143 pain detection in humans, 11 in insects, 10-11 pansies, pigmentation in, 65-66 paper paper versus plastic bags, 112-114 recycling, 111 parallel universes, 191-193 parasitic plants, 55-56 Passenger Pigeon, 46 Pasteurella multocida, 41 Pelean eruptions, 133 phases of moon, 173-174 photons, 96, 195 photos of moon landing sites, 174-175
215
photosynthesis, 54 Physics of the Impossible (Kaku), 193 A Piece of Wood (Bradbury), 79 pigmentation fading in sunlight, 81 of flowers, 63-66 of leaves, 59-60 Plait, Philip, 190 planets orbit of, 201 rotation of, 199-200 plants anthocyanins, 59-60 dodder, 55 flower pigmentation, 63-66 four-leafed clover, 66 fruits living nature of, 72-73 ripening process, 58-59 seedless fruits, 57-58 genetic modification of, 67-68 leaves, movement in wind, 71-72 mistletoe, 55 parasitic plants, 55-56 plant neurobiology, 54 relationship between plant/animal life, 53-54 trees roots, 62-63 water ascent in, 60-61 xylem, 60 Venus flytrap, 53 walking palm, 53 plasma universe theory, 192 plastic paper versus plastic bags, 112-114 recycling, 112
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216
plate tectonics. See also earthquakes, 132, 137-142 and formation of oceans, 130 Caribbean plate movement, 140-141 Enriquillo–Plantain Garden Fault, 140 Pacific Plate movement, 143 San Andreas Fault system, 143 Plinian eruptions, 133 Pliny the Elder, 26 ploidy, 57 Plug, Cornelis, 172 polar day, 156-157 polar night, 156-157 polarity reversals, 151-152 Poles polar night/day, 156-157 viewing sun setting and rising at same time, 156 Polo, Marco, 134 porch lights, greenhouse gases emitted by, 116-117 Potts, Wayne, 28 pouch hygiene in marsupials, 32 precipitation droughts, 107-108 impact of climate change on, 108-109 U.S. precipitation patterns by geographic area, 102-103 predicting time of sunrise, 155 primary waves (earthquakes), 138 Project Cirrus, 97 Project Stormfury, 97 protons, 95 Proxima Centauri, 185 Pythagorean theorem, 166
plate tectonics
Q-R quarks, 95 quasars, light from, 187 radiation from big bang, 186 ionizing radiation, 78 irradiated gemstones, 78-79 radio signals, 88 radiometric dating, 144 rain droughts, 107-108 impact of climate change on, 108-109 rainwater, 82 U.S. precipitation patterns by geographic area, 102-103 rainbows, 163-165 rainwater, 82 rapid freezing phenomenon, 85-86 Rayleigh waves (earthquakes), 138 recycling aluminum, 111 environmental soundness of, 111-112 glass, 112 paper, 111 plastic, 112 textiles, 110-111 refractive index, 76-77 regional temperatures, 121-122 relativity, theory of, 93, 195 remote controls, 88 rerouting hurricanes, 97-98 retired storm names, 100 revolution of moon, 171-172 ribonucleic acid (RNA), 45 Richards, E. G., 161
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species
Richter, Charles, 137 Richter scale, 137 rime frost, 87 ripening process (fruits), 58-59 RNA (ribonucleic acid), 45 Roddenberry, Gene, 183 Rømer, Ole, 92 roots of trees, 62-63 rose pigmentation, 63-64 Ross, Helen, 172 rotation of planets, 171-172, 199-200 of vortexes, 105-106 Russell, Jeffrey Burton, 153 Rutherford, Ernest, 96 Ryder, Oliver, 37
S S waves (earthquakes), 138 saliva (canine), 40-41 salt, adding to boiling water, 75-76 salt water, metal corrosion in, 79-80 San Andreas Fault system, 143 sap sweetness of trees, 60 satellites, GRACE (Gravity Recovery And Climate Experiment), 146-147 Schwarzchild radius, 196 sea levels, rise in, 68-69 sea water chemicals in, 82 metal corrosion in, 79-80 temperature, increase in, 68 seasons meteorological seasons versus astronomical seasons, 162-163 seasonal color changes in animals, 50-51 secondary waves (earthquakes), 138
217
seeding hurricanes, 97 seedless fruits, 57-58 sewage treatment, 114-115 Shapiro, Ascher, 107 sky, color of, 169 sleep defined, 4 in dolphins, 34-35 in fruit flies, 4 in spiders, 4-5 in whales, 34-35 snails adhesive mucus, 32-33 Olividae family, 33-34 soap bubbles, shape of, 81 solar cycles, 120 solar flares, 152 solar nebula, 200 solstices seasons and, 162-163 summer solstice, 158-159 winter solstice, 157-160 songs of crickets, 21 sounds freeway noise, 89-90 songs of crickets, 21 speed of sound, impact of air temperature on, 90 Southeast, precipitation in, 103 Southern Ocean, 129 Southwest droughts in, 108 precipitation in, 103 space burials, 182-183 spacetime, 94-95 species behavioral constraints and extinction, 46-47 definition of, 43-44 genetic overlap, 44-46
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218
speed of light, 195 calculating, 92 upper limit on speeds, 92-93 of sound, impact of air temperature on, 90 spiders circadian rhythm, 4 consumption of mosquitoes, 1-2 sleep in, 4-5 webs, 2-3 spiracles, 14 stars, death of, 201-202 static electricity, 90-91 sterility, hybrid sterility, 42 strength of hurricanes, 98 stridulation, 21 string theory, 192 Strombolian eruptions, 133 subatomic particles, forces between, 96 subsidence, 131-132 summer dog days of summer, 158 summer solstice, 158-159 sun alignment with center of Milky Way on December 21, 2012, 203 sunlight colors fading in, 81 hair bleaching in, 81-82 sunrise, predicting time of, 155 sunset, green flash at, 170 viewing sun setting and rising at same time, 156 sundials, 158 sunlight colors fading in, 81 hair bleaching in, 81-82
speed
supercooled water, 86 superior mirage, 164 superposition compound eyes, 15 swimbladder, 49 switching on/off lights, 116 syrup making, 60
T tears, 39-40 telescopes, 194 temperature. See also freezing water, 84-87 absolute zero, 89 average regional and global temperatures, 121-122 cooling houses, 87 estimating from crickets’ chirp rates, 21 heat, 88-89 impact of air temperature on speed of sound, 90 relationship with solstices, 157-158 thermal conductivity, 82-83 teosinte, 67 textiles, recycling, 110-111 theory of relativity, 93 theory of special relativity, 195 thermal conductivity, 82-83 Thiemens, Mark, 136 13-month calendar systems, 161 Three Gorges Dam, 146 tides, 178 in Great Lakes, 131 tilt of Earth on axis, 139, 150 time spacetime, 94-95 time dilation, 94 time of sunrise, predicting, 155
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Wallace, Alfred Russel
219
toilets direction of toilet flush, 105-107 water usage, 114 tomatoes, ripening process, 58-59 Torino scale, 179 tornadoes, causes of, 101-102 towels, recycling, 110-111 trachea in ants, 14 tracheoles in ants, 14 trees anthocyanins, 59-60 roots, 62-63 sap sweetness, 60 water ascent in, 60-61 xylem, 60 tropical cyclones, naming, 100 tropical depressions, naming, 100 Tschinkel, Walter, 15 TVs energy consumption, 115-116 remote controls, 88
mini black holes, 198 warping of space near, 196-197 calculating distance from Earth to other galaxies, 183-184 calculating velocities of distant objects, 184-185 dark energy, 188 dark matter, 198-199 death of stars, 201-202 expansion of, 186-189, 195 geometry of, 190-191 infinite or finite, 191 membrane theory, 192 origins of, 192-193 parallel universes, 191-193 planets orbit of, 201 rotation of, 199-200 plasma universe theory, 192 quasars, light from, 187 upper limit on speeds, 92-93
U
V
U.S. Naval Oceanography Portal, 155 Union of Concerned Scientists, 67 United States precipitation patterns drought, 107-108 impact of climate change on, 108-109 patterns by geographic area, 102-103 universe big bang, 186, 192 black holes light trapped in, 195-196 maximum size of, 197
velocities of distant objects, measuring, 184-185 Venus flytrap, 53 vision flicker fusion frequency (FFF), 29-31 in bees, 15-16 optokinetic response, 31 volcanic eruptions, 132-134 vortexes, rotation of, 105-106 Vulcanian eruptions, 133
W walking palm, 53 Wallace, Alfred Russel, 149
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220
warp drive, 189 water. See also oceans, 113, 129-130 boiling water, adding salt to, 75-76 color changes in wet fabric, 80 freezing frost formation, 86-87 icicles on ice cubes, 85 Mpemba effect, 84-85 rapid freezing phenomenon, 85-86 rainwater, 82 sea water chemicals in, 82 metal corrosion in, 79-80 supercooled water, 86 toilet water use, 114 water ascent in trees, 60-61 watermelons, seedless, 57-58 weakening hurricanes, 97-98 weakly interacting massive particles (WIMPs), 198 weather Hadley Circulation, 104 hurricanes development of, 98-99 eye, 99 eyewall, 99 global warming and, 99 strength of, 98 weakening or rerouting, 97-98 ice ages glacial/interglacial cycles, 117-120 Little Ice Age, 118-119
warp drive
jet stream, 103-104 mesocyclones, 101 tornadoes, causes of, 101-102 tropical cyclones, naming, 100 tropical depressions, naming, 100 webs (spider) construction of, 3 movement of spiders in, 2-3 weight of Earth, 145-148 whales, sleep in, 34-35 White Wilderness (documentary), 48 WIMPs (weakly interacting massive particles), 198 wind, leaf movement in, 71-72 winter solstice, 157-160 WMO (World Meteorological Organization), 100 wobble of Earth on axis, 150 World Meteorological Organization (WMO), 100
X-Y-Z xylem, 60 yolks, green color in hard-boiled egg yolks, 75 Yucca Mountain, 126 zooxanthellae, 69
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