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Early life signatures in sulfur and carbon isotopes from Isua, Barberton, Wabigoon (Steep Rock), and Belingwe Greenstone Belts (3.8 to 2.7 Ga)

By
N.V. Grassineau
N.V. Grassineau
1
Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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P. Abell
P. Abell
2
Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 02881, USA
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P.W.U. Appel
P.W.U. Appel
3
Geological Survey of Denmark and Greenland (GEUS), Oester Voldgade 10, 1350 Copenhagen, Denmark
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D. Lowry
D. Lowry
4
Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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E.G. Nisbet
E.G. Nisbet
4
Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK
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Published:
January 01, 2006

Carbon and sulfur isotopes have been measured on samples from four Archean greenstone belts dating from 3.8 Ga to 2.7 Ga, in order to trace metabolic changes as life evolved over this one-billion-year period. In the Isua Greenstone Belt (3.8 Ga), Greenland, δ34S in sulfide minerals from sedimentary sequences range from −3.8‰ to +3.4‰. δ13Cred measured in BIFs, turbidites and conglomerates vary from −29.6‰ to −14.7‰; this range permits us to hypothesize the presence of hyperthermophilic and chemotrophic species in transient settings, or possibly pelagic photoautotrophic microbes, or both. In the Barberton Greenstone Belt, South Africa, sulfide minerals show δ34S values from +1.5‰ to +5.6‰. Black shales have δ13Cred values from −32.4‰ to −5.7‰, suggesting that oxygenic photosynthetic and sulfate-reducing bacteria were present by ca. 3.24 Ga. The δ13Cred measured in the stromatolites of Steep Rock Lake (3.0 Ga), Ontario, Canada, are from −30.6‰ to −21.6‰, giving clear evidence for occupation of a shallow water environment by cyanobacteria. The wide isotopic ranges for δ34S in sulfides from −21.1‰ to +16.7‰ and for δ13Cred in carbon-rich cherts and black shales from −43.4‰ to −7.2‰ in the Belingwe Greenstone Belt, Zimbabwe, indicate that photosynthetic microbial mat communities were well established at 2.7 Ga. In these well-preserved Late Archean formations, modern-style biological sulfur and carbon cycles may have been in operation. The δ34S and δ13Cred ranges, respectively 37‰ and 36‰, indicate a great variety of biological processes interacting with each other.

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GSA Memoirs

Evolution of Early Earth's Atmosphere, Hydrosphere, and Biosphere - Constraints from Ore Deposits

Stephen E. Kesler
Stephen E. Kesler
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Hiroshi Ohmoto
Hiroshi Ohmoto
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Geological Society of America
Volume
198
ISBN print:
9780813711980
Publication date:
January 01, 2006

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