Early Earth's environment: An exobiological perspective

The purpose of this review is to assess the current state of our knowledge of the physico-chemical conditions that prevailed on the early Earth when Life originated. The early Earth environment was subjected to a very peculiar flux of primordial matter and solar energy. It may have therefore displayed physico-chemical conditions very different from today. The terrestrial geological record can potentially provide a lot of information about these ancient times. Their direct study is strongly influenced by the preservation of the oldest terrains and in particular the survival of volcano-sedimentary supracrustal rocks (ie remnants of the outer part of the Earth's surface), formed by a direct interaction with the hydrosphere, atmosphere and, possibly, primitive biosphere. Their study in recent years helped to clarify the existence of a primitive ocean, to study its physico-chemical conditions, but also to use the elemental and isotopic composition of sediments as a tracer of some key atmospheric chemical processes of biotic or abiotic origin. Studying and understanding the primitive terrestrial environment at the most ancient times the geological record allows us to access, possibly as far back as 4.28 billion years, allow us already to glimpse these unique conditions, certainly limited in time, which constituted nevertheless a prelude to, or even fostered, Life and its evolution on our home planet