Abstract:

The inaccessible and enigmatic core of the Earth comprises 1/3 of the planet's mass, gives rise to the magnetic field, and holds clues to the Earth's formation and the nature of its building blocks. It is comprised mainly of an Fe–Ni alloy, plus ~10% lighter elements whose identities and abundances remain unknown. Here we describe several distinct approaches to constraining the core’s composition. A geo-/cosmochemical approach involves comparing the compositions of the bulk silicate Earth and the Earth’s building blocks to determine the core's composition, especially for moderately volatile elements. High pressure–temperature mineral physics data can be used to identify which light elements, at specific abundance levels, are able to match the core's seismic properties (e.g., density, sound velocities, liquidus phase relations). The range of light element contents can also be constrained by incorporating metal–silicate partitioning results into models of Earth’s core formation, which offers insight into not only the Earth's core composition but also the conditions and mechanisms of core formation.