23 Jul 2003 20:28 AR AR194-AA41-11.tex AR194-AA41-11.sgm LaTeX2e(2002/01/18) P1: GCE 10.1146/annurev.astro.41.071601.170049 Annu. Rev. Astron. Astrophys. 2003. 41:429–63 doi: 10.1146/annurev.astro.41.071601.170049 Copyright c 2003 by Annual Reviews. All rights reserved First published online as a Review in Advance on June 4, 2003 EVOLUTION OF A HABITABLE PLANET James F. Kasting1 and David Catling2 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802; email:
[email protected] 2Department of Atmospheric Sciences and Astrobiology Program, University of Washington, Seattle, Washington 98195-1640; email:
[email protected] Key Words climate history, habitable zones, planetary volatiles, rise of atmospheric oxygen, biosignature gases ■ Abstract Giant planets have now been discovered around other stars, and it is only a matter of time until Earth-sized planets are detected. Whether any of these planets are suitable for life depends on their volatile abundances, especially water, and on their climates. Only planets within the liquid-water habitable zone (HZ) can support life on their surfaces and, thus, can be analyzed remotely to determine whether they are inhabited. Fortunately, current models predict that HZs are relatively wide around main-sequence stars not too different from our sun. This conclusion is based on studies of how our own planet has evolved over time. Earth’s climate has remained conducive to life for the past 3.5 billion years or more, despite a large increase in solar luminosity, probably because of previous higher concentrations of CO2 and/or CH4.