Mechanisms and Geochemical Models of Core Formation

This chapter reviews the mechanisms by which metal and silicate segregate to form the cores and mantles of planetary bodies. It also reviews geochemical models of core formation and considers the implications of these for the evolution of mantle and core chemistries. Many studies in recent years have concluded that core formation in Earth involved extensive chemical equilibration between metal and silicate at high pressures. The chapter discusses two mechanisms that are consistent with such equilibration, namely grain-scale percolation and metal-silicate segregation in a magma ocean. Earth's mantle is depleted in siderophile elements, relative to chondritic and Solar System abundances, because of extraction into the core. The degree of depletion depends on the metal-silicate partition coefficient. Accretion and core-mantle differentiation of the terrestrial planets can now be modeled by combining astrophysical simulations of planetary accretion with geochemical models of core formation.