ANR Atmofossil

Résumé du projet

The timing of the emergence and the early evolutionary stages of life on Earth remains enigmatic. Organic matter preserved in Archean (4.0-2.5 Ga) sedimentary rocks may record these early evolutionary stages, but organic traces of life in such ancient rocks are challenging to distinguish from non-biological (abiotic) organic structures that may display similar morphological and geochemical features. An important source of abiotic organic matter on the Archean Earth, not yet investigated, could come from atmospheric synthesis. Yet, very little is known about the geochemical fate of such Archean abiotic aerosols during geological burial, hence, about their geochemical signatures in Archean rocks. Therefore, I propose to tackle this issue by combining laboratory experiments to synthesize analogues of Archean organic aerosols and to submit them to simulated geological burial processes. Analogues of Archean organic aerosols will be synthesized through cold plasma discharge experiments in gaseous mixtures thought to compose the Archean atmosphere (N2, CO2, CH4). The synthesized organic aerosols will then be submitted to simulated geological burial processes in sapphire anvil cells coupled with UV-resonant Raman spectromicroscopy to investigate the morphological and molecular transformations of both organic and mineral phases during the experiments. The morphology and the elemental and molecular compositions of the experimental products will be further characterized using SEM, TEM, and XANES microspectroscopy. Such experimental constraints on the morphological, elemental and molecular signals that may have been left by abiotic atmospheric synthesis in the Archean geological record of organic matter are mandatory to further distinguish biotic from abiotic Archean organics, and mitigate controversies about traces of early life activity on Earth.

Liste des membres du LGL-TPE impliqués :

• Julien Alleon
• Felicia Haase
• Hervé Cardon
• Gilles Montagnac
• Clémentine Fellah
• Isabelle Daniel