Journal
PLOS ONE
Volume 11, Issue 1, Pages -Publisher
PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0147629
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Funding
- Deutsche Forschungsgemeinschaft (DFG Priority Programme 1833, Building a Habitable Earth) [DU 1450/3-1]
- Courant Research Centre of the University Gottingen (DFG, German Excellence Program)
- Gottingen Academy of Sciences and Humanities
- University of New South Wales
- Sloan Foundation
- National Institute for Mathematical and Biological Synthesis (NIMBioS)
- National Science Foundation
- U.S. Department of Homeland Security
- U.S. Department of Agriculture through NSF Award [EF-0832858]
- University of Tennessee, Knoxville
- University of Gottingen
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Paleoarchean rocks from the Pilbara Craton of Western Australia provide a variety of clues to the existence of early life on Earth, such as stromatolites, putative microfossils and geo-chemical signatures of microbial activity. However, some of these features have also been explained by non-biological processes. Further lines of evidence are therefore required to convincingly argue for the presence of microbial life. Here we describe a new type of microbial mat facies from the 3.4 Ga Strelley Pool Formation, which directly overlies well known stromatolitic carbonates from the same formation. This microbial mat facies consists of laminated, very fine-grained black cherts with discontinuous white quartz layers and lenses, and contains small domical stromatolites and wind-blown crescentic ripples. Light-and cathodoluminescence microscopy, Raman spectroscopy, and time of flight-secondary ion mass spectrometry (ToF-SIMS) reveal a spatial association of carbonates, organic material, and highly abundant framboidal pyrite within the black cherts. Nano secondary ion mass spectrometry (NanoSIMS) confirmed the presence of distinct spheroidal carbonate bodies up to several tens of mu m that are surrounded by organic material and pyrite. These aggregates are interpreted as biogenic. Comparison with Phanerozoic analogues indicates that the facies represents microbial mats formed in a shallow marine environment. Carbonate precipitation and silicification by hydrothermal fluids occurred during sedimentation and earliest diagenesis. The deciphered environment, as well as the delta C-13 signature of bulk organic matter (-35.3 parts per thousand), are in accord with the presence of photoautotrophs. At the same time, highly abundant framboidal pyrite exhibits a sulfur isotopic signature (delta S-34 = +3.05 parts per thousand;Delta S-33 = 0.268 parts per thousand; and Delta S-36 = -0.282 parts per thousand) that is consistent with microbial sulfate reduction. Taken together, our results strongly support a microbial mat origin of the black chert facies, thus providing another line of evidence for life in the 3.4 Ga Strelley Pool Formation.
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