NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This study was supported by Contract/Grant No. SB 1341-06-Z-0011, TO #2 between the National Academy of Sciences and the Technology Administration of the U.S. Department of Commerce; Contract/Grant No. SLON 2005-10-18 between the National Academy of Sciences and the Alfred P. Sloan Foundation; and Contract/Grant No. P116Z05283 between the National Academy of Sciences and the U. S. Department of Education. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.

Library of Congress Catalog Card Number: 2008926521

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Cover: The cover design depicts a possible far distant future configuration bringing nearly all of the earth’s land mass into a single supercontinent, including merging the Americas into Asia.