Session Abstract: During most of the geologic past, life and the surface environments on Earth were profoundly different than they are today. In particular, it is generally accepted that the atmosphere was devoid of O2, or nearly so, until the "Great Oxidation Event" approximately 2.4 billion years ago. However, considerable uncertainty remains about the abundances of O2 and other oxidants during the first half of Earth history, as well as processes that constrained these abundances to seemingly trace levels. Emerging data should allow tighter constraints on Archean free oxygen concentrations, the variability of redox conditions at high temporal resolution, and the evolutionary and biogeochemical consequences of oxygenation. At the same time there is a need to refine existing proxies, assess their limitations, and develop new ones. This session will explore these issues. We encourage abstracts from a variety of areas ranging from analytical and theoretical geochemistry to genomics. For more information see
http://www.agu.org/meetings/fm09/program/scientific_session_search.php?show=detail&sessid=219 Source: NAI Newsletter
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