ACCRETION AND PRIMARY DIFFERENTIATION OF THE EARTH: A PERSONAL JOURNEY

Abstract

The accretion of the Earth was a violent series of events dominated by the addition of objects one third to one tenth of the mass of the growing planet. During the later stages of accretion, these collisions deposited enough energy to at least partly melt the Earth, possibly multiple times. The result was an ocean of magma. Metal sank through this magma ocean and ponded at its base at roughly the depth of the base of the current upper mantle for some period of time before transiting diapirically through the lower mantle to the center of the planet. Metal appears to have equilibrated with silicate at the base of the magma ocean. The primitive atmosphere and ocean appear to have outgassed from the magma ocean. Core formation, magma ocean solidification, ocean and atmospheric outgassing were essentially complete by 4.45 Ga ago.