Documentation of primitive terrestrial life signatures and the methods
used to characterize them will be relevant to identify signatures of
biological origin at the surface of Mars. In this respect, fossils of
chemolithotrophic microorganisms found in ancient volcanic rocks on
Earth are used as analogues for the kinds of microorganisms that could
be found on Mars. Indeed, chemolithotrophs are the ancient forms of life
thought to inhabit the first habitats on Earth and potentially on Mars
when the two planets had similar conditions in their early history, i.e.
an atmosphere, geological activity and enough liquid water in specific
habitable localities for a prolonged period of time.