interactive student edition Visit our Web site at www.macmillanmh.com Program Authors Dr. Dorothy J. T. Terman Dr. Jay K. Hackett Science Curriculum Development Consultant Former K–12 Science and Mathematics Coordinator Irvine Unified School District, CA Professor Emeritus of Earth Sciences University of Northern Colorado Dr. Richard H. Moyer Professor of Science Education and Natural Sciences University of Michigan–Dearborn Dr. Gerald F. Wheeler Executive Director National Science Teachers Association Bank Street College of Education Dr. JoAnne Vasquez New York, NY Elementary Science Education Consultant NSTA Past President Member, National Science Board and NASA Education Board Contributing Authors Mulugheta Teferi, M.A. Principal, Gateway Middle School St. Louis Public Schools St. Louis, MO Dinah Zike, M.Ed. Dinah Might Adventures LP San Antonio, TX Kathryn LeRoy, M.S. Dr. Sally Ride Sally Ride Science San Diego, CA Lucille Villegas Barrera, M.Ed. Elementary Science Supervisor Houston Independent School District Houston, TX Dr. Stephen F. Cunha Professor of Geography Humboldt State University Arcata, CA Executive Director Division of Mathematics and Science Education Miami-Dade County Public Schools, FL Students with print disabilities may be eligible to obtain an accessible, audio version of the pupil edition of this textbook. Please call Recording for the Blind & Dyslexic at 1-800-221-4792 for complete information. A Published by Macmillan/McGraw-Hill, of McGraw-Hill Education, a division of The McGraw-Hill Companies, Inc., Two Penn Plaza, New York, New York 10121. Copyright © 2008 by Macmillan/McGraw-Hill. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, network storage or transmission, or broadcast for distance learning. is a tradema