Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2012 Sep 18;109(38):15146-51. doi: 10.1073/pnas.1207491109. Epub 2012 Sep 4.
The 3.45-billion-year-old Strelley Pool Formation of Western Australia preserves stromatolites that are considered among the oldest evidence for life on Earth. In places of exceptional preservation, these stromatolites contain laminae rich in organic carbon, interpreted as the fossil remains of ancient microbial mats. To better understand the biogeochemistry of these rocks, we performed microscale in situ sulfur isotope measurements of the preserved organic sulfur, including both Δ(33)S and . This approach allows us to tie physiological inference from isotope ratios directly to fossil biomass, providing a means to understand sulfur metabolism that is complimentary to, and independent from, inorganic proxies (e.g., pyrite). Δ(33)S values of the kerogen reveal mass-anomalous fractionations expected of the Archean sulfur cycle, whereas values show large fractionations at very small spatial scales, including values below -15‰. We interpret these isotopic patterns as recording the process of sulfurization of organic matter by H(2)S in heterogeneous mat pore-waters influenced by respiratory S metabolism. Positive Δ(33)S anomalies suggest that disproportionation of elemental sulfur would have been a prominent microbial process in these communities.
澳大利亚西部 34.5 亿年历史的斯特雷利池组地层保存了叠层石，它们被认为是地球上最古老的生命证据之一。在保存完好的地方，这些叠层石含有富含有机碳的纹层，被解释为古代微生物席的化石遗迹。为了更好地了解这些岩石的生物地球化学，我们对保存下来的有机硫进行了微尺度原位硫同位素测量，包括 Δ(33)S 和。这种方法使我们能够将同位素比值得出的生理推断直接与化石生物量联系起来，为理解硫代谢提供了一种方法，这种方法与无机示踪剂（例如黄铁矿）相辅相成，且独立于无机示踪剂。干酪根的 Δ(33)S 值揭示了太古宙硫循环中预期的质量异常分馏，而值则在非常小的空间尺度上显示出很大的分馏，包括低于-15‰的值。我们将这些同位素模式解释为记录了在受呼吸 S 代谢影响的异质席孔隙水中 H(2)S 对有机质的硫化过程。正的 Δ(33)S 异常表明，元素硫的歧化作用将是这些群落中一个突出的微生物过程。
