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Science 17 April 2009:
Vol. 324. no. 5925, pp. 370 - 373
DOI: 10.1126/science.1169289
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Reports

Anomalous Fractionations of Sulfur Isotopes During Thermochemical Sulfate Reduction

Yumiko Watanabe,1* James Farquhar,2 Hiroshi Ohmoto1

Anomalously fractionated sulfur isotopes in many sedimentary rocks older than 2.4 billion years have been widely believed to be the products of ultraviolet photolysis of volcanic sulfur dioxide in an anoxic atmosphere. Our laboratory experiments have revealed that reduced-sulfur species produced by reactions between powders of amino acids and sulfate at 150° to 200°C possess anomalously fractionated sulfur isotopes: {Delta}33S = +0.1 to +2.1 per mil and {Delta}36S = –1.1 to +1.1 per mil. These results suggest that reactions between organic matter in sediments and sulfate-rich hydrothermal solutions may have produced anomalous sulfur isotope signatures in some sedimentary rocks. If so, the sulfur isotope record of sedimentary rocks may be linked to the biological and thermal evolution of Earth in ways different than previously thought.

1 The NASA Astrobiology Institute and Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA.
2 Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.

* To whom correspondence should be addressed. E-mail: yumiko{at}geosc.psu.edu

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