Revisiting the Thermal Conductivity of Iron at Earth’s Core-Mantle Boundary

The thermal conductivity of Earth’s core is a key parameter to investigate thermal evolution of the Earth, as well as the characteristics of the dynamo which drives Earth’s magnetic field, however it has been the subject of intense controversy. At the heart of this controversy are the persistent discrepancies between direct measurements of iron thermal conductivity, ab initio calculations of thermal and electrical conductivity and experimental electrical conductivity measurements.  Here we present new data on the thermal conductivity of hcp-Fe up to 135 GPa and 3000 K, combined with direct X-ray based methods for the in situ measurement of sample geometry – the largest source of uncertainty in thermal conductivity measurements. Our results reaffirm a ‘low’ thermal conductivity for iron at the conditions of Earth’s core-mantle boundary, but revise this value upwards to between 60 W/m/K and 80 W/m/K which can be reconciled with the lower end of values reported using ab initio theory and electrical experiments.