Microbial life and biogeochemical cycling on land 3,220 million years ago

Type Article
Date 2018-09
Language English
Author(s) Homann MartinORCID1, Sansjofre Pierre1, Van Zuilen Mark2, Heubeck Christoph3, Gong Jian2, Killingsworth Bryan1, Foster Ian S.1, Airo Alessandro4, Van Kranendonk Martin J.5, 6, Ader Magali3, Lalonde Stefan1
Affiliation(s) 1 : European Inst Marine Studies, CNRS, UMR6538, Lab Geosci Ocean, Technopole Brest Iroise, Plouzane, France.
2 : Inst Phys Globe Paris, CNRS, UMR7154, Paris, France.
3 : Friedrich Schiller Univ, Dept Geosci, Jena, Germany.
4 : Tech Univ Berlin, Ctr Astron & Astrophys, Berlin, Germany.
5 : Univ New South Wales, Australian Ctr Astrobiol, Sydney, NSW, Australia.
6 : Univ New South Wales, Sch Biol Earth & Environm Sci, Sydney, NSW, Australia.
Source Nature Geoscience (1752-0894) (Nature Publishing Group), 2018-09 , Vol. 11 , N. 9 , P. 665-671
DOI 10.1038/s41561-018-0190-9
WOS© Times Cited 66

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 (delta C-13(org)) from these mats define a narrow range centred on -21 parts per thousand, in contrast to fossil mats of marine origin from nearby tidal deposits that show delta C-13(org) values as low as -34 parts per thousand. Bulk nitrogen isotope compositions (2 < delta N-15 < 5 parts per thousand) are also significantly different from their marine counterparts (0 < delta N-15 < 3 parts per thousand), 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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Homann Martin, Sansjofre Pierre, Van Zuilen Mark, Heubeck Christoph, Gong Jian, Killingsworth Bryan, Foster Ian S., Airo Alessandro, Van Kranendonk Martin J., Ader Magali, Lalonde Stefan (2018). Microbial life and biogeochemical cycling on land 3,220 million years ago. Nature Geoscience, 11(9), 665-671. Publisher's official version : https://doi.org/10.1038/s41561-018-0190-9 , Open Access version : https://archimer.ifremer.fr/doc/00638/74977/