The colonization of emergent continental landmass by microbial life was an evolutionary step of paramount importance in Earth history. Here we report direct fossil evidence for life on land 3,220 million years ago (Ma) in the form of terrestrial microbial mats draping fluvial conglomerates and gravelly sandstones of the Moodies Group, South Africa. Combined field, petrographic, carbon isotope and Raman spectroscopic analyses confirm the synsedimentary origin and biogenicity of these unique fossil mats as well as their fluvial habitat. The carbon isotope compositions of organic matter (δ13Corg) from these mats define a narrow range centred on −21‰, in contrast to fossil mats of marine origin from nearby tidal deposits that show δ13Corg values as low as −34‰. Bulk nitrogen isotope compositions (2 < δ15N < 5‰) are also significantly different from their marine counterparts (0 < δ15N < 3‰), which we interpret as reflecting denitrification in the terrestrial habitat, possibly of an atmospheric source of nitrate. Our results support the antiquity of a thriving terrestrial biosphere during the Palaeoarchaean and suggest that a complex and microbially driven redox landscape existed during the deposition of the Moodies Group, with distinct biogeochemical cycling occurring on land by 3,220 Ma.

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This work was greatly supported by LabexMER ANR-10-LABX-19 and Prestige COFUND-GA-2013-609102 to M.H., and Deutsche Forschungsgemeinschaft (DFG) grant He2418/13–1 to C.H. S.V.L. and M.V.Z. acknowledge support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement n° 716515 for S.V.L. and grant agreement n° 646894 for M.V.Z.). We thank N. and D. Oosthuizen for access to the private Mountainlands nature reserve, S. Bläsing and M. Grund for assistance with sample collection, J.-P. Oldra for thin section preparation, and O. Lebeau, C. Tanvet, C. Liorzou, M.-L. Rouget and B. Gueguen for assistance with isotopic and elemental analysis.

Author information


  1. European Institute for Marine Studies, CNRS-UMR6538 Laboratoire Géosciences Océan, Technopôle Brest-Iroise, Plouzané, France

    • Martin Homann
    • , Pierre Sansjofre
    • , Bryan Killingsworth
    • , Ian S. Foster
    •  & Stefan V. Lalonde
  2. Institut de Physique du Globe de Paris, CNRS-UMR7154, Paris, France

    • Mark Van Zuilen
    •  & Jian Gong
  3. Department of Geosciences, Friedrich-Schiller-Universität, Jena, Germany

    • Christoph Heubeck
    •  & Magali Ader
  4. Center of Astronomy and Astrophysics, Technische Universität Berlin, Berlin, Germany

    • Alessandro Airo
  5. Australian Centre for Astrobiology, and School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia

    • Martin J. Van Kranendonk


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M.H. and C.H. carried out fieldwork and collected samples in South Africa. P.S., M.A. and S.V.L. helped with the acquisition and interpretation of elemental and isotopic data. M.V.Z. and J.G. performed Raman analysis. B.K., I.S.F., A.A. and M.J.V.K. contributed to the discussion of the data. M.H. wrote the manuscript with contributions from all co-authors.

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The authors declare no competing interests.

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Correspondence to Martin Homann.

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