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The Earth and the Moon The Earth and the Moon Linda T. Elkins-Tanton The Earth and the Moon Copyright © 2006 by Linda T. Elkins-Tanton All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Elkins-Tanton, Linda T. The Earth and the moon / Linda T. Elkins-Tanton. p. cm. — (Solar system) Includes bibliographical references and index. ISBN 0-8160-5194-1 (acid-free paper) 1. Earth—Popular works. 2. Moon—Popular works. I.Title. QB631.2.E45 2006 525—dc22 2005014189 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Chelsea House on the World Wide Web at http://www.chelseahouse.com Text and cover design by Dorothy M. Preston Illustrations by Richard Garratt Printed in the United States of America VB CH 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. To Tim Grove, Brad Hager, Maria Zuber, Sam Bowring, and my other friends at the Massachusetts Institute of Technology who worked at turning me into a scientist, with special appreciation for the research we did about the Moon. Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii PART ONE: THE EARTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. The Earth: Fast Facts about a Planet in Orbit . . . . . . . . . . . . . . . . . . 3 Fundamental Information about the Earth . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. The Interior of the Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Moment of Inertia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 The Brittle Crust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 The Solid but Moving Mantle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 High-Pressure Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Rheology, or How Solids Can Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 The Solid and Liquid Cores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Magnetic Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 Temperatures, Pressures, and Compositions . . . . . . . . . . . . . . . . . . . . . . . 51 What Is Pressure? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3. The Early Evolution of the Planet Earth . . . . . . . . . . . . . . . . . . . . . 57 Elements and Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4. The Visible Planet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 How Old Is the Earth’s Surface? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Surface Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Determining Age from Radioactive Isotopes . . . . . . . . . . . . . . . . . . . . . . . . 76 Volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Earthquakes . . . . . . . . . . . . . . . . . . . . . . . . . . .