The young Sun and the atmosphere and photochemistry of the early Earth

Abstract

The origin and evolution of the Earth's early atmosphere depend crucially on the dissipation time t_N of the primitive solar nebula, SN. Using different theories of turbulence, we estimate that for a 0.1 M_solar SN, t_N is 2.5-8.3Myr. Because accretion times are usually much longer, we conclude that most planetary accretion must have occurred in a gas-free environment. Using new IUE data, a wavelength-dependent UV flux is constructed for the young Sun which is then used to study the photochemistry and concentrations of O, O₂, O₃, OH, H, HCO and formaldehyde H₂CO in the Earth's early prebiological atmosphere.