This proposal documents habitability on the early Earth and at the surface of Mars in the past
and the present. Habitability is commonly understood as “the potential of an environment
(past or present) to support life of any kind”. Having liquid water at the surface of a planet is
probably the minimum condition for habitability. However, several other parameters control
the environmental conditions necessary for a planet to harbor life. Therefore, a
multidisciplinary approach, uniting expertise, from geochemistry to numerical modeling is
proposed to investigate the habitability of Early Earth and Mars; the latter, originally displayed
many similarities to Earth but then evolved along a very different path. First, we study the
effect of planetary differentiation (core formation, large impacts, plate tectonics) on
conditioning habitability. Second, we develop new geochemical biosignatures (Se and Ga)
tracers, test them and then combine them with existing ones (e.g. Zn and Cu) to detect and
characterize early terrestrial life, and its responses to major geological events (impact
cratering, huge magmatic event). To do so, case studies have been selected: A Proterozoic
impact structure in Australia (Acraman) and a major Archean magmatism in Canada (Abitibi).
Finally, data collected by ongoing and future space missions to Mars is used to document the
past and present habitability of the red planet in comparison to Earth.