3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence

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Science  22 Oct 1993:
Vol. 262, Issue 5133, pp. 555-557
DOI: 10.1126/science.11539502


Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.

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