6533b86dfe1ef96bd12c92a3

RESEARCH PRODUCT

Molecular preservation of organic microfossils in Paleoarchean cherts

subject

description

International audience; Fossilization processesandthe increase of temperature and pressure conditions associated withburialinevitably alter the original biochemical signatures of organic molecules.At a certain stage, biogenic and abiotic organic structures may become undistinguishable [1].Cherts (i.e.silica-rich rocks)are well known forthe morphologicalpreservationof fossilized microorganisms.Recently,spatially resolvedinvestigations usingsynchrotron-based XANESmicrospectroscopyrevealedthatmolecular information about the organic precursor of3.4 Gamicrofossils, was preservedintheStrelley Pool chert(Pilbara, Western Australia),despite a metamorphichistory so far believed to be incompatible with such preservation(lower greenschist facies-peak temperature ≅300 °C;[2]).Laboratory experiments showed that silica-organic interactions are likely to play a key rolein the molecular preservation of microorganismsfossilized in cherts[3].Altogether,these resultsdemonstratethat ancient organic microfossils may exhibit a high level of chemical preservation in appropriate settings independent of a long and complex geological history.Here, weusespatially resolvedmicrospectroscopy techniques, includingSTXM-based XANES spectroscopy,to investigate the chemical nature andmolecularpreservation ofindividualmicrofossils from the3.4 GaBuck Reef chert(Barberton, SouthAfrica). The latter experiencedslightly higherpeaktemperatureconditions(≅360 °C)during their geological historycompared to the Strelley Pool chert.These molecular data providekeyconstraintsto understandingthe impactof increasing metamorphic temperatureon thepreservation of theorganic moleculescomposing some of the oldest microbial fossils on the Earth.