Coupled Fe and S isotope evidence for Archean microbial Fe(III) and sulfate reduction
- 1Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK, and Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK
- 2Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK
Abstract
Direct fossil evidence for early microbial life on Earth is rare. Microbiological data indicate that sulfate and iron reduction are both among the earliest forms of microbial respiration, and direct evidence for the early origin of sulfate reduction comes from sulfur isotopic anomalies in ancient sediments. Fe isotope geochemistry potentially provides a new way of identifying microbial iron reduction early in Earth's history. We present Fe isotopic data for sedimentary pyrite from the 2.7 Ga Belingwe sedimentary basin in Zimbabwe. Isotopically light Fe and a remarkable covariation between Fe and S isotopes provide strong evidence for coexisting Fe and S reduction. Our results are consistent with an early origin for sulfate reduction and provide direct geochemical evidence for the antiquity of bacterial Fe reduction. The covariation of Fe and S isotopes may provide a useful new tracer of microbial evolution early in Earth history.
Footnotes
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↵GSA Data Repository item 2006030, Table DR1, Fe isotopic compositions, and Appendix, is available online at www.geosociety.org/pubs/ft2006.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
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- Accepted 31 October 2005.
- Received 20 July 2005.
- Revision received 27 October 2005.
- Geological Society of America
