Compressibility change in iron-rich melt and implications for core formation models

Metallic iron, in both solid and liquid states, is the dominant component of Earthʹs core. Density measurements of molten iron containing an appropriate amount of light elements (5.7 wt.% carbon) identified a liquid–liquid transition by a significant compressibility increase in the vicinity of the δ-γ-liquid triple point at 5.2 GPa. This transition pressure coincides with a marked change in the pressure evolution of the distributions of nickel, cobalt and tungsten between liquid metal and silicate melt that form a cornerstone of geochemical models of core formation. The identification of a clear link between molten metal polymorphism and metal–silicate element partitioning implies that reliable geochemical core formation models will need to incorporate the effects of these additional liquid metal transitions.