  The formation of the Earth's core is a consequence of planetary accretion and
processes in the Earth's interior. The mechanical process of planetary
differentiation is likely to occur in large, if not global, magma oceans
created by the collisions of planetary embryos. Metal-silicate segregation in
magma oceans occurs rapidly and efficiently unlike grain scale percolation
according to laboratory experiments and calculations. Geochemical models of the
core formation process as planetary accretion proceeds are becoming
increasingly realistic. Single stage and continuous core formation models have
evolved into multi-stage models that are couple to the output of dynamical
models of the giant impact phase of planet formation. The models that are most
successful in matching the chemical composition of the Earth's mantle, based on
experimentally-derived element partition coefficients, show that the
temperature and pressure of metal-silicate equilibration must increase as a
function of time and mass accreted and so must the oxygen fugacity of the
equilibrating material. The latter can occur if silicon partitions into the
core and through the late delivery of oxidized material. Coupled dynamical
accretion and multi-stage core formation models predict the evolving mantle and
core compositions of all the terrestrial planets simultaneously and also place
strong constraints on the bulk compositions and oxidation states of primitive
bodies in the protoplanetary disk.
