Abstract
Abundant graphitized organic matter within 3.7-billion-year-old sediments in the Isua Supracrustal Belt comprises the oldest remnants of life. This organic matter could have provided a favorable substrate for anaerobically respiring microbes, though their existence in the early Archean remains uncertain. Here we assess whether anaerobic respiration, linked to reduction of iron and sulfur, operated within these ancient sediments. We analyzed carbon and sulfur isotope data from pelagic and turbiditic sedimentary rocks, sampled from a rock core, and used petrography and iron concentrations to provide geological context. Carbon isotopic compositions indicate respiration of organic compounds, with lighter values associated with iron-rich samples, consistent with respiration coupled to iron reduction. Sulfide grains in pelagic layers have isotopic compositions consistent with reduction of atmospherically produced elemental sulfur, possibly with minor contributions from sulfate reduction during sedimentary hiatuses. These results suggest that early Archean ecosystems were sustained by multiple, interacting microbial metabolisms.
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Data availability
Sulfur and carbon isotope data, as well as iron, titanium, and aluminum concentrations measured directly on the rock core, are provided in the supplementary data and are also available from the following repository: https://doi.org/10.17894/ucph.62287630-6632-4b1f-9641-ad529d5e8bca.
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Acknowledgements
We are grateful for assistance provided by Nozomi Matsuda during the acquisition of sulfur isotopic data. This project was made possible through financial support provided by the Novo Nordisk Foundation through NERD grant NNF21OC0068372. Research and export permits for rock core materials were granted by the Greenlandic self-government.
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A.J.B. led the writing of the paper, while T.H. provided regular feedback. A.J.B., T.H., M.A.R.H., and M.T.R. contributed to data interpretation. M.T.R. collected the sample material. M.A.R.H., E.A.B., and A.J.B. conducted sample preparation, characterization, and compositional analysis. E.A.B. and A.J.B. carried out data reduction. E.A.B., M.T.R., and T.H. provided analytical equipment and materials. All authors contributed to the editing and review of the paper.
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Boyd, A.J., Harding, M.A.R., Bell, E.A. et al. Evidence for diverse anaerobic metabolisms in 3.7-billion-year-old marine detrital sediments. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03188-6
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DOI: https://doi.org/10.1038/s43247-026-03188-6
