Evolution of an impact-induced atmosphere and magma ocean on the accreting Earth

Early rapid formation of the atmosphere and hydrosphere on the terrestrial planets has recently been proposed1,2. Here we present a quantitative study of this process during accretion by planetesimal impacts. These impacts increase the surface temperature and thus affect the formation of either a proto-atmosphere or a proto-hydrosphere by degassing of volatiles. We show that an impact-induced H2O atmosphere increases the surface temperature of the Earth to a stage where a magma ocean is possible, with the total amount of H2O in the proto-atmosphere clustering around 1021kg, this number is rather insensitive to variations in the input data. We suggest that the apparent coincidence of the H2O abundance in the proto-atmosphere with the present mass (˜1.4 × 1021kg) of the ocean is evidence for an impact origin for the atmosphere and hydrosphere.