Metallic iron, in both solid and liquid states, is the dominant component of Earth's 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. © 2011 Elsevier B.V.