Sedimentary Organic Matter Preservation and Atmospheric O2 Regulation
The global cycles of organic carbon (OC) and molecular oxygen (O2) are inextricably linked by the fact that both substances are uniquely produced and destroyed in equimolar amounts by photosynthesis and respiration. These oppos1ng processes have been balanced on the geochemical equivalent of a knife’s edge for at least the last 600 million years, over which 02 dependent metazoans are continuously represented in the geologic record. Throughout this period, 02 release from the preservation of organic matter (~50 wt% OC) in marine sediments has been closely compensated for by simultaneous uptake of O2 during weathering of organic matter (and reduced inorganic minerals) in continental rocks. In this way, the atmospher1c reservoir of O2 has been maintained within the relatively narrow concentration range (±50%), above which runaway vegetation fires occur and below which anoxia becomes deadly to multicellular life (Berner 1989). Given that the mean residence time of atmospheric O2 is four million years with respect to contemporary sedimentary OC bur1al, over the last 600 million years the Earth’s global O2 control system has had roughly 30o chances to fail on either the side of conflagration and anoxia — and has not (Walker 1974; Watson et al. 1978; Garrels et al. 1976; Jones and Chaloner 1991). Such an extended planetary winning streak, at least from a human perspective, suggests the existence of an effective control system for global-scale cycling of bioactive elements for at least the most recent eighth of Earth history (Van Valen 1971; Petsch and Berner 1998).
KeywordsSulphide Geochemistry Fractionation Biodegradation Petrol
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