Peering into the Cradle of Life: multiple sulphur isotopes reveal insights into environmental conditions and early sulphur metabolism some 3.5 Ga ago
Final Report Abstract
The Archean world was much different from today. The atmosphere contained no free oxygen, yet abundant carbon dioxide and methane. The oceans contained abundant dissolved iron, but sulfate was low. Life was entirely microbial and is believed to have exclusively inhabited the marine realm. Reconstructing environmental conditions, but also tracing ancient metabolic pathways have substantially benefited from the application of stable isotopes. With respect to the Archean sulfur cycle, sources and processes can be identified through characteristic mass-dependent and mass-independent sulfur isotopic signatures. As part of the multinational and multidisciplinary research project “Peering into the Cradle of Life” under the auspices of the International Continental Scientific Drilling Program (ICDP), multiple sulfur isotopes (i.e. 32S, 33S, 34S, and 36S) were determined for sulfide and sulfate from Paleoarchean (ca. 3.5 – 3.2 billion years old) sedimentary and volcanic rocks from the Barberton Greenstone Belt, South Africa. Key results reveal important insights into sulfur cycling on the early Earth: Sulfur in near-surface environments is largely of atmospheric origin, following UV-driven photochemical reactions of volcanogenic sulfur dioxide in an essentially oxygen-free atmosphere. - The sulfur isotopic composition of volcanic rocks suggests the interaction between seawater and oceanic crustal rocks. - Sulfur isotopes clearly reveal different forms of microbial sulfur cycling, notably sulfate reduction, elemental sulfur disproportionation, and sulfide oxidation.
Publications
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(2015) Paleoarchean sulfur cycling: multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa. Precambrian Research 267:311-322
Montinaro, A., Strauss, H., Mason, P.R.D., Roerdink, D., Münker, C., Schwarz-Schampera, U., Arndt, N., Farquhar, J., Beukes, N.J., Gutzmer, J., Peters, M.
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(2016) Sulphur Tales from the Early Archean World. International Journal of Astrobiology 15, 177-185
Montinaro, A., Strauss, H.
