Biological soil crusts as modern analogs for the Archean continental biosphere: insights from carbon and nitrogen isotopes.

Christophe Thomazo (1) , Estelle Couradeau (2, 3) , Anna Giraldo-Silva (4) , Johanna Marin-Carbonne (5) , Arnaud Brayard (1) , Martin Homann (6, 7) , Pierre Sansjofre (7, 8) , Stefan Lalonde (7) , Ferran Garcia-Pichel (4)

1 BGS - Biogéosciences [UMR 6282]
2 LBNL - Lawrence Berkeley National Laboratory [Berkeley]
3 DOE Joint Genome Institute [Walnut Creek]
4 Center for Fundamental and Applied Microbiomics
5 ISTE - Institut des sciences de la terre [Lausanne]
6 Department of Earth Sciences [UCL London]
7 LGO - Laboratoire Géosciences Océan
8 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie

Stable isotope signatures of elements related to life such as carbon and nitrogen can be powerful biomarkers that provide key information on the biological origin of organic remains and their paleoenvironments. Marked advances have been achieved in the last decade in our understanding of the coupled evolution of biological carbon and nitrogen cycling and the chemical evolution of the early Earth thanks, in part, to isotopic signatures preserved in fossilized microbial mats and organic matter of marine origin. However, the geologic record of the early continental biosphere, as well as its evolution and biosignatures, is still poorly constrained. Following a recent report of direct fossil evidence of life on land at 3.22 Ga, we compare here the carbon and nitrogen isotopic signals of this continental Archean biosphere with biosignatures of cyanobacteria biological soil crusts (cyanoBSCs) colonizing modern arid environments. We report the first extended δ13C and δ15N data set from modern cyanoBSCs and show that these modern communities harbor specific isotopic biosignatures that compare well with continental Archean organic remains. We therefore suggest that cyanoBSCs are likely relevant analogs for the earliest continental ecosystems. As such, they can provide key information on the timing, extent, and possibly mechanism of colonization of the early Earth's emergent landmasses.

Mots clés: Archean; Carbon isotope; Early life; Isotope biosignature; Nitrogen isotope

Domaines: Géochimie

Christophe Thomazo, Estelle Couradeau, Anna Giraldo-Silva, Johanna Marin-Carbonne, Arnaud Brayard, et al.. Biological soil crusts as modern analogs for the Archean continental biosphere: insights from carbon and nitrogen isotopes.. Astrobiology, 2020, 20 (7), pp.815-819. ⟨10.1089/ast.2019.2144⟩. ⟨hal-02976854⟩