Sulfur Chemistry and Sulfate Reducing Bacteria of Archean Oceans

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Analyses of the published sulfur isotopic data on bulk rock samples of Archean sediments have led to a new model for the Archean atmosphere-ocean-biosphere system: the oceans, as far back as about 3.8-3.2 billion years ago, were already sulfate rich with a sulfate concentration of about 1/3 of the present level, were 30- 40 oC warmer than modern oceans, and supported a very high activity of sulfate reducing bacteria world wide; the early Archean atmosphere already contained appreciable amounts of free oxygen. The objective of the proposed research is to test the above and other models for the Archean atmosphere-ocean-biosphere by examining the sulfur-carbon-iron chemistry and the microscopic- scale variation in the sulfur, carbon and oxygen isotopic compositions of sediments from the Warrawoona Group, Australia; the Isua Group, Greenland; and the Fig Tree Group, South Africa, using a state-of-the-art stable isotope ratio mass spectrometer equipped with a laser ablation system.