Résumé
The evidence is increasingly strong that microorganisms developing around marine hydrothermal systems (thermophilic prokaryotes) were the first living community on Earth. Owing to the delicate nature of fossil microorganisms and inherent difficulties for discriminating between true fossils from artifacts, an important challenge for microbiologists and geochemists is to extract unequivocal beogenic information from individual microfossils using high-resolution and non-destructive techniques. Here, we report sub-micron scale mapping of transition metals (Fe, Zn and Cu) and sulfur oxidation states in individual filamentous microfossils using micro- PIXE (Proton Induced X-ray Emission) and synchrotron micro-XANES (X-ray Absorption Near Edge Structure) techniques. The sample studied consists of branching iron-oxide filaments encapsulated with amorphous silica from a fragment of an inactive chimney of the East Pacific Rise. Our results suggest that the original microorganisms were actively metabolising sulfur, and show the potential of the approach used for tracking microbial markers exploiting the full range of the sulfur-redox spectrum in fossilized hydrothermal systems.