Thermochemical convection in Earth’s inner core

The dynamics of Earth's inner core depends critically on whether it is stably stratified or unstably stratified. We propose here a general analysis of the thermal evolution of the inner core. Whether the geotherm in the inner core is superadiabatic or not depends on the inner core solidification rate, on the thermal diffusivity of iron at inner core conditions, and on the ratio of the Clapeyron slope to the adiabatic gradient in the inner core. The temperature field within the inner core can be destabilizing-and could drive convection-if the growth of the inner core is fast enough. The effect of radiogenic heating is probably small, and, perhaps surprisingly, can even stabilize the inner core against convection. The uncertainties are such that it is not possible at present to conclude about the likelihood of thermal convection in the inner core, but recent estimates of the Core-Mantle Boundary (CMB) heat flux and inner core conductivity favour convection. Thermal convection is more likely early in the inner core history, a consequence of the secular decrease in cooling rate of the core. In addition, solidification-induced partitioning of the light elements may induce a stable density stratification within the inner core.