Water-induced mantle overturn explains high Archean paleointensities

As a consequence of the evolution of the water-bearing basal magma ocean, water-induced mantle overturn can suitably explain many puzzling observations in the Archean, including the formation of continents and the Archean-Proterozoic boundary. The upwelling of the hot basal magma ocean during mantle overturn drastically affects the thermal state of the core-mantle boundary and geomagnetic field. We model the thermal evolution of the core-mantle boundary to investigate the effects of mantle overturn on the geomagnetic field. Our results demonstrate that mantle overturn substantially accelerates core cooling and increases heat flow across the core-mantle boundary. Such enhanced heat flow would have strengthened the geomagnetic field, which explains well the high paleointensity records from ∼3.5 to 2.5 Ga. The strong geodynamo and formation of Archean continents generate a concordant picture of the evolution of water-induced mantle overturn.