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Anomalous Fractionations of Sulfur Isotopes During Thermochemical Sulfate Reduction

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Science  17 Apr 2009:
Vol. 324, Issue 5925, pp. 370-373
DOI: 10.1126/science.1169289

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Abstract

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: Δ33S = +0.1 to +2.1 per mil and Δ36S = –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.

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