2002 Annual Science Report
Pennsylvania State University Reporting | JUL 2001 – JUN 2002
Evolution of Atmospheric O2, Climate, and Biosphere - James F. Kasting
Progress has been made in three different areas. First, Alex Pavlov and I have completed a set of calculations and a paper on the topic of mass-independent fractionation (MIF) of sulfur isotopes in Archean rocks. We have shown that the observation of MIF in rocks older than 2.3 Ga implies that atmospheric O2 levels were < 10-5 times present levels at that time. In combination with the measurements obtained by James Farquhar and others, this essentially resolves the ongoing debate about when atmospheric O2 first rose.
Second, Alex and I have also published two papers on methane photochemistry in anoxic atmospheres. One is a detailed model of the photochemical reactions. We showed that a hydrocarbon haze may have formed, but that it would not have been optically thick enough to provide an effective solar ultraviolet (UV) screen. The second paper argued that the isotopically light (in 13C) kerogens in 2.7-b.y. old Archean sediments may represent the remnants of that haze.
Finally, we have also taken initial steps in modeling Archean ecosystems. Janet Siefert, Pushker Kharecha, and I have been creating a numerical model of an anaerobic, methanogen-based Archean ecosystem. We hope to use this model to predict the methane concentration in the Archean atmosphere both before and after the invention of oxygenic photosynthesis.
PROJECT MEMBERS:James Kasting
RELATED OBJECTIVES:Objective 12.0
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet.