The degree of biogenicity of micrites and terrestrial Mars analogues

A number of indications, as the past presence of water, a denser atmosphere and a mild climate on early Mars, suggest that environmental conditions favorable to the emergence of life must have been present on that planet in the first hundred million years, or even more recently. If life actually existed on Mars, biomarkers could be still preserved with some degree of degradation. In previous laboratory works we have investigated the infrared spectral modifications induced by thermal processing on different carbonate samples, in the form of recent shells and fossils of different ages, whose biogenic origin is indisputable. The goal was to develop a method able to discriminate carbonate biogenic samples from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced carbonates deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed among the oldest traces of biological activity known on Earth. This result is of valuable importance since such carbonates are linked to primitive living organisms which can be considered as good analogues for putative Martian life forms. In this work we show that, studying different parts of the same carbonate rock sample, we are able to distinguish, on the base of the degree of biogenicity, the various micrite types (i.e. detrital vs autochthonous).