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Molecular Evidence of Late Archean Archaea and the Presence of a Subsurface Hydrothermal Biosphere

Gregory T. Ventura, Fabien Kenig, Christopher M. Reddy, Juergen Schieber, Glenn S. Frysinger, Robert K. Nelson, Etienne Dinel, Richard B. Gaines and Philippe Schaeffer
Proceedings of the National Academy of Sciences of the United States of America
Vol. 104, No. 36 (Sep. 4, 2007), pp. 14260-14265
Stable URL: http://www.jstor.org/stable/25436659
Page Count: 6
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Molecular Evidence of Late Archean Archaea and the Presence of a Subsurface Hydrothermal Biosphere
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Abstract

Highly cracked and isomerized archaeal lipids and bacterial lipids, structurally changed by thermal stress, are present in solvent extracts of 2,707- to 2,685-million-year-old (Ma) metasedimentary rocks from Timmins, ON, Canada. These lipids appear in conventional gas chromatograms as unresolved complex mixtures and include cyclic and acyclic biphytanes, C₃₆-C₃₉ derivatives of the biphytanes, and C₃₁-C₃₅ extended hopanes. Biphytane and extended hopanes are also found in high-pressure catalytic hydrogenation products released from solvent-extracted sediments, indicating that archaea and bacteria were present in Late Archean sedimentary environments. Postdepositional, hydrothermal gold mineralization and graphite precipitation occurred before metamorphism (≈2,665 Ma). Late Archean metamorphism significantly reduced the kerogen's adsorptive capacity and severely restricted sediment porosity, limiting the potential for post-Archean additions of organic matter to the samples. Argillites exposed to hydrothermal gold mineralization have disproportionately high concentrations of extractable archaeal and bacterial lipids relative to what is releasable from their respective high-pressure catalytic hydrogenation product and what is observed for argillites deposited away from these hydrothermal settings. The addition of these lipids to the sediments likely results from a Late Archean subsurface hydrothermal biosphere of archaea and bacteria.

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