Thermal structure of the lower mantle and core

The low thermal diffusivity of Earth’s rocks and its large size signify that even today, thermal transport in the lower mantle and core are independent of that in the outer layers. This situation permits construction of thermal profiles of the deep Earth from internal constraints: namely, the two-phase metallic core follows the solidus of iron alloy, and the top of the lower mantle lies below the dry peridotite solidus. Thermal conductivity of the core is irrelevant. Without samples, mantle thermal conductivity is estimated considering data and models for dense solids, leading to “hot silicate” and “cold oxide” geotherms. Temperatures are reasonably constrained, except for the height and position of the local maximum in the lower mantle. Meteoritic values for radionuclide contents of the lower mantle are consistent with present-day temperatures and progressive melting of the core.