Earth’s energy budget and the “New Core Paradox”

Earth’s magnetic field has existed for billions of years, sustained by a hydromagnetic dynamo operating in the liquid iron core. The fundamental question of how the dynamo has been powered over geological timescales has received renewed interest in recent years owing to advances in experimental and computational mineral physics. Much debate has surrounded the core’s thermal conductivity, which could be high enough to pose significant problems for the classic model of core evolution where the dynamo is assumed to be powered by secular cooling before the growth of the solid inner core. The “New Core Paradox” refers to the failure of the classic model to predict sufficient power for the dynamo over geological time, in conflict with paleomagnetic observations. Here I review the basis for the “New Core Paradox” and then consider 4 proposed resolutions to the paradox that augment the classic model: radiogenic heating in the core; a hot initial core and low melting point; precipitation of light elements at the core-mantle boundary; and coupled thermo-chemical interactions between the core and a basal magma ocean. Finally I discuss the observations that might distinguish these different scenarios.