Powering Earth's Ancient Dynamo With Silicon Precipitation

Earth's core has produced a global magnetic field for the last 4 Gyrs, presently sustained by inner core growth.Models of the core with high thermal conductivity suggest potentially insufficient power available for the geodynamo prior to inner core formation ~1 Ga.Precipitation of SiO2 from the liquid core might offer an alternative power source for the magnetic field before inner core growth, however, no estimates of partition coefficient exist for conditions of the early core.We present the first determination of the silicon partition coefficient at core-mantle boundary conditions and use these results to build a thermodynamic model that is integrated into a model of coupled core-mantle thermal evolution.We show that models including precipitation of silicon can satisfy constraints of inner core size, mantle convective heat flux, mantle temperature and a persistent ancient geodynamo whilst those excluding fail.Successful power from precipitation favours an oxygen poor initial core composition.