2024-03-05 08:28:48
The chert volcanic sediments of Kitty’s Gap (Pilbara, Australia), a 3.45 billion year old rock formation, were deposited in a shallow water environment. They were thus able to provide an ideal habitat for certain types of microorganisms on early Earth, such as chemolithotrophs, which use the oxidation of inorganic substrates as a source of energy. Formed in conditions similar to those of Mars, the volcanic sediments of ancient rocks should make it possible to test different analytical techniques which will be necessary for the search for traces of life in their counterparts, deposited on the red planet during the Noachian more than 3.5 billion years. However, the small cell size of the microorganisms that lived on the surface and inside these terrestrial sediments combined with the diffuse nature of these fossilized colonies makes the identification and characterization of potential biosignatures in these types of organisms particularly difficult. rocks.
Scientists from the Center for Molecular Biophysics (CNRS/University of Orléans) implemented a battery of spectroscopic techniques (optical microscopy, Raman spectroscopy, LA-ICP-MS, etc.) to establish syngenicity and biogenicity fossil remains preserved in these sediments.
The results show that the sediments were deposited in a semi-enclosed basin, influenced by tides, rivers and hydrothermal fluids, whose conditions are compatible with the colonization and development of microbial life. Elementary and molecular morphological analyzes of the carbonaceous material associated with the degraded remains of potential microfossils confirmed its syngenicity and biogenicity. In particular, the researchers carried out elementary (X-ray fluorescence and photon-induced X-ray emission–PIXE) and molecular (UV and IR fluorescence) analyses. These analytical techniques revealed an enrichment in trace metals (vanadium, chromium, iron, cobalt, etc.) as well as in aromatic and aliphatic molecules associated with carbonaceous matter, which supports the hypothesis of a biological origin. Transmission electron microscopy observations also made it possible to identify amorphous nanostructures which were interpreted as degraded remains of microorganisms and their by-products (e.g. extracellular polymeric substances, filaments).
The study highlights the need to use a wide range of complementary analyzes at multiple scales to search for life in extraterrestrial samples brought back to Earth. These results, to which the Physics of Two Infinitys Laboratory (CNRS/University of Bordeaux), the Archaeomaterials Research Institute (CNRS/University of Orléans) as well as the Natural History Museum of London and the University of Bologna, have just been published in the journal Astrobiology.
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