The chemical composition of the early terrestrial atmosphere: Formation of a reducing atmosphere from CI-like material

The chemical composition of Earth's early atmosphere is likely to have played an important role in the origin of life. In particular, the redox state of Earth's early atmosphere may have controlled greatly the efficiency of abiotic synthesis of biologically important organic compounds. However, the chemical composition of the Earth's early atmosphere has not been studied extensively before. In this study, we theoretically estimate the chemical composition of an atmosphere near the end of the completion of planetesimal accretion of the Earth. Our calculation results show that the Earth's early atmosphere is very reducing, rich in H₂ and/or CH₄, regardless of which meteoritic materials accrete and regardless of which chemical reactions control the molecular abundance in the atmosphere. In other words, impact-degassed origin of Earth's atmosphere leads inevitably to a reducing chemical composition, which is very favorable to efficient prebiotic synthesis of organic matter on Earth.