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Science 2 December 2005:
Vol. 310. no. 5753, pp. 1477 - 1479
DOI: 10.1126/science.1117824
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Reports

Active Microbial Sulfur Disproportionation in the Mesoproterozoic

David T. Johnston,1*{dagger} Boswell A. Wing,1*{dagger} James Farquhar,1 Alan J. Kaufman,1 Harald Strauss,2 Timothy W. Lyons,3 Linda C. Kah,4 Donald E. Canfield5

The environmental expression of sulfur compound disproportionation has been placed between 640 and 1050 million years ago (Ma) and linked to increases in atmospheric oxygen. These arguments have their basis in temporal changes in the magnitude of 34S/32S fractionations between sulfate and sulfide. Here, we present a Proterozoic seawater sulfate isotope record that includes the less abundant sulfur isotope 33S. These measurements imply that sulfur compound disproportionation was an active part of the sulfur cycle by 1300 Ma and that progressive Earth surface oxygenation may have characterized the Mesoproterozoic.

1 Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA.
2 Geologisch-Paläontologisches Institut und Museum der Westfälischen Wilhelms, Universität Münster, Corrensstraße 24, D-48149 Münster, Germany.
3 Department of Earth Science, University of California, Riverside, CA 92521, USA.
4 Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA.
5 Nordic Center for Earth Evolution and Institute of Biology, Southern Denmark University, Campusvej 55, 5230 Odense M, Denmark.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: dtj{at}geol.umd.edu (D.T.J.); wing{at}essic.umd.edu (B.A.W.)

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