Energetically Expensive Dynamo Action in Earth’s Basal Magma Ocean

Previous studies, focusing on the electrical conductivity and thermal evolution of an early magma ocean at the base of Earth’s mantle, have found that basal magma ocean (BMO) convection could have produced the ancient geomagnetic field. By advances in high-resolution dynamo modeling, we find that convection in a thin BMO-like spherical shell is able to sustain strong, axially-aligned dipolar magnetic fields. However, integrating our dynamo results with updated thermal evolution and rotating convective turbulence models implies that an Earth-like magnetic field was unlikely to have been generated in the BMO, a finding relevant to the interpretation of ancient paleomagnetic signatures, Earth’s global-scale dynamics, and long-term planetary evolution.