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Science 22 October 1993:
Vol. 262. no. 5133, pp. 555 - 557
DOI: 10.1126/science.11539502
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Articles

Science, Vol 262, Issue 5133, 555-557
Copyright © 1993 by American Association for the Advancement of Science

articles

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

H Ohmoto, T Kakegawa, and DR Lowe

Department of Geosciences, The Pennsylvania State University, University Park 16802, USA.

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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Science. ISSN 0036-8075 (print), 1095-9203 (online)