Chris Davies , Sam Greenwood

Thermo-chemical interactions at the core-mantle boundary (CMB) play an integral role in determining the dynamics and evolution Earth's deep interior. This review considers the processes in the core that arise from heat and mass transfer at the CMB, with particular focus on thermo-chemical stratification and the precipitation of oxides. A fundamental parameter is the thermal conductivity of the core, which we estimate as k = 70-110 W/m/K at CMB conditions based on consistent extrapolation from a number of recent studies. These high conductivity values imply the existence of an early basal magma ocean (BMO) overlying a hot core and rapid cooling potentially leading to a loss of power to the dynamo before the inner core formed around 0.5-1 Gyrs ago, the so-called ``new core paradox''. Coupling core thermal evolution modelling and calculations of chemical equilibrium between liquid iron and silicate melts suggests that FeO dissolved into the core after its formation, creating a stably stratified chemical layer below the CMB, while precipitation of MgO and SiO2 was delayed until the last 2-3 Gyrs and was therefore not available to power the early dynamo; however, once initiated, precipitation supplied ample power for field generation. We also present a possible solution to the new core paradox without requiring precipitation or radiogenic heating using k = 70 W/m/K. The model matches the present inner core size and heat flow and temperature at the top of the convecting mantle. It predicts a present-day CMB heat flow of 8.5 TW, a chemically stable layer 100 km thick, and a BMO lifetime of 2 Gyrs.