Evolution of an Impact-Generated H2O–CO2Atmosphere and Formation of a Hot Proto-Ocean on Earth

Abstract
Due to impact degassing during accretion, a hot H2O-rich proto-atmosphere was possibly formed on the growing Earth. We investigate the evolution of an impact-generated H2O–CO2 atmosphere at the final stage of accretion by using a one-dimensional radiative-convective atmosphere model. Since atmospheric pressure is high (∼200 bar) and close to the critical point of water vapor (647 K, 220 bar), we need to take into account the nonideal behavior of gases in the calculation. It is shown that the surface temperature suddenly decreases when the impact (accretion) energy flux decreases to about 150 W m−2, and that a proto-ocean is formed on the growing Earth. The estimated temperature of a proto-ocean is consistent with that of an archaean ocean estimated from the oxygen isotope data.

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