A Very Weakly Reducing Atmosphere Prior to the Rise in Atmospheric Oxygen

Details A Very Weakly Reducing Atmosphere Prior to the Rise in Atmospheric Oxygen A Very Weakly Reducing Atmosphere Prior to the Rise in Atmospheric Oxygen

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmpp21a..06c&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #PP21A-06

Biology

0325 Evolution Of The Atmosphere (1610, 8125), 1022 Composition Of The Hydrosphere, 4912 Biogeochemical Cycles, Processes, And Modeling (0412, 0414, 0793, 1615, 4805), 5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5225 Early Environment Of Earth

Scientific paper

We describe the photochemistry of stable anoxic atmospheres in response to declining fluxes of reducing gases. The goal is to understand the atmospheric consequences of increases in the oxidation state of the surface ocean prior to the Great Oxidation Event, when Earth's atmosphere first transitioned from weakly reducing to weakly oxidizing on a global scale approximately 2.4 billion years ago (Ga). Drill cores of the 2.5 Ga Mt. McRae shale reveal evidence for free oxygen availability in Earth's surface ocean, and perhaps require the presence of a trace amount of surficial free oxygen to induce oxidative weathering of the continents (Anbar et al., 2007 ; Kaufman et al., 2007). Simultaneous co-detection of a mass-independent sulfur isotope (MIF S) signal indicates generally reducing conditions must have existed throughout the troposphere (Zahnle et al., 2006) at this time. Using a simple box model, we had previously predicted (Claire et al., 2006) that such an atmosphere might exist as a result of likely evolutionary models of planetary fluxes. This work will use detailed photochemical models to investigate the vertical dependence of methane photolysis, OH production, SO2 photolysis, and S8 deposition in very weakly reducing atmospheres that may have proceeded the Great Oxidation Event. Anbar et al."A Whiff of Oxygen Before the Great Oxidation Event?" Science, 2007, in press Claire et al."Biogeochemical modelling of the rise in atmospheric oxygen." Geobiology, 4, 239-269, 2006. Kaufman et al."Late Archean biospheric oxygenation and atmospheric evolution." Science, 2007, in press. Zahnle et al."The loss of mass-independent fractionation in sulfur due to a Paleoproterozoic collapse of atmospheric methane." Geobiology, 4, 271-283, 2006.

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