Molecular and organic carbon isotopic evidence for the evolution of key metabolic pathways during the Archean-Proterozoic transition

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A sequence of events defines Earth’s irreversible oxygenation some 2.35 Ga ago: the first substantial rise in atmospheric oxygen abundance and a subsequent increase in oxidative continental weathering and corresponding riverine delivery of dissolved oxidized compounds (e.g. sulphate) into oxic marine surface waters. In contrast, deep waters remain anoxic; they were either ferruginous or even sulphidic. As a consequence of these profound changes in the redox structure of the sedimentary realm, the entire microbial network from autotrophic carbon fixation to heterotrophic carbon recycling must have changed as well, both in respect to diversity and position in the environment. Characteristic carbon isotope values archive the operation of respective biologically mediated processes. Even more diagnostic are organic molecules, biomarkers for individual organisms, metabolic pathways or environmental conditions. Temporal and spatial changes in biogeochemical carbon turnover across the Archean-Proterozoic transition and as a result of Earth’s oxygenation will be reconstructed via a systematic survey of organic carbon isotopes and detailed biomarker work for selected stratigraphic intervals.