The effects of a layer of high internal heating in D on the Earth's magnetic history

Recently, it has been proposed that a layer of high internal heating exists in D". Arguments for such a layer have come both from geochemical considerations and from thermal modeling of core evolution. In this contribution, we present the results of numerical modeling of the thermal evolution of the Earth with high degrees of internal heating in the D" region. The models consist of a fluid-mechanical model for convection in the mantle that is coupled to a parameterized model for the thermal evolution of the core. The model includes the effects of inner core freezing and the entropy that is available for ohmic dissipation is calculated as a proxy for the intensity of the geodynamo action. We find that the effects of a layer of high internal heating in D" often include heat flowing from the mantle into the core in early Earth history which would make impossible the existence of an early function geodynamo. We conclude that a layer of high internal heating in D" must be considered unlikely on geodynamical grounds.