Element partitioning constraints on the light element composition of the Earth's core

Partitioning of sulfur (S), oxygen (O) and silicon (Si) between liquid Fe‐Ni‐alloy (LA) and liquid silicate (LS) was studied with a multi‐anvil apparatus at pressures between 2 and 25 GPa and temperatures between 2073 and 2623 K. We found that S has a strong affinity for liquid Fe‐Ni‐alloy at all the experimental conditions investigated. Partition coefficient of S between liquid Fe‐Ni‐alloy and liquid silicate ( D S LA/LS ) increases with pressure and decreases with temperature. At the proposed pressure and temperature of core‐mantle equilibrium during early Earth differentiation [ Li and Agee , 1996; Righter et al ., 1997], S is highly siderophile ( D S LA/LS ∼ 1000), while Si and O are highly lithophile ( D Si LA/LS , D O LA/LS < 0.03). Our study suggests that if the core composition was largely established by equilibrium partitioning in a deep magma ocean, then S is the most plausible principle light element in the core.