^1,2James Badro, ³John P. Brodholt, ^1,2Hélène Piet, ¹Julien Siebert, ⁴Frederick J. Ryerson
¹Institut de Physique du Globe de Paris, Sorbonne Paris Cité, UMR CNRS 7154, 75005 Paris, France
²Earth and Planetary Science Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
³Department of Earth Sciences, University College London, London WC1E 6BT, United Kingdom;
⁴Lawrence Livermore National Laboratory, Livermore, CA 94550

We combine, for the first time to our knowledge, two approaches to study Earth’s core composition: a geochemical approach based on trace element depletion in the mantle and a geophysical approach based on a seismically lighter and faster (than pure iron−nickel) core. The joint approach allows making strong statements; first of all, as opposed to the current belief, Earth must have accreted material that is more oxidized than the present-day mantle, similar to that of planetesimals such as 4-Vesta, and got reduced to its present state during core formation. Secondly, core light-element concentrations in those conditions are 2.7% to 5% oxygen alongside 2% to 3.6% silicon; the oxygen concentrations in the core are higher than previously thought, and, conversely, silicon concentrations are lower than previous estimates.

Reference
Badro J, Brodholt JP, Piet H, Siebert J, Ryerson FR (2015) Core formation and core composition from coupled geochemical and geophysical constraints. Proceedings of the National Academy of Sciences 112, 12310-12314
Link to Article [doi:10.1073/pnas.1505672112]