Melting boundary of Fe‐17%Si up to 5.5 GPa and the timing of core formation

Melting of Fe‐17wt%Si has been investigated at temperatures up to 1600°C and pressures up to 5.5 GPa in a cubic anvil press. The melting temperature, T M , was identified with the discontinuity in temperature and pressure dependence of electrical resistance. Two types of electrode materials, Pt and Fe, were used and gave consistent melting results. T M increases with pressure from 1200°C at 1 atm to 1430°C at 5.5 GPa. dT M /dP decreases with pressure and reaches a value of zero at P∼5 GPa. Combined with the thermal profiles of the proto‐Earth, the pressure independence of the melting boundary of Fe‐17%Si at the highest pressures of this study suggests core formation began early in Earth accretion with a substantial liquid metal phase fraction between 30 Ma and 42 Ma.