The “New Core Paradox”: Challenges and Potential Solutions

The “new core paradox” suggests that the persistence of the geomagnetic field over nearly all of Earth history is in conflict with the core being highly thermally conductive, which makes convection and dynamo action in the core much harder prior to the nucleation of the inner core. Here we revisit this issue by exploring the influence of six important parameters on core evolution: upper/lower mantle viscosity ratio, core thermal conductivity, core radiogenic heat rate, mantle radiogenic heating rate, central core melting temperature, and initial core-mantle boundary (CMB) temperature. Each parameter is systematically explored by the model, which couples mantle energy and core energy-entropy evolution. A model is “successful” if the correct present-day inner core size is achieved and the dynamo remains alive, as implied by the paleomagnetic record. In agreement with previous studies, we do not find successful thermal evolutions using nominal parameters, which includes a core thermal conductivity of 70 Wm−1K−1, zero core radioactivity, and an initial CMB temperature of 5,000 K. The dynamo can be kept alive by assuming an unrealistically low thermal conductivity of 20 Wm−1K−1 or an unrealistically high core radioactive heat flow of 3 TW at present-day, which are considered “unsuccessful” models. We identify a third scenario to keep the dynamo alive by assuming a hot initial CMB temperature of ∼6,000 K and a central core liquidus of ∼5,550 K. These temperatures are on the extreme end of typical estimates, but should not be ruled out and deserve further scrutiny.