Physical State of the Earth's Core

Abstract

The physical state of the Earth's core depends on its thermal regime. In any discussion of the Earth one begins with the simplest possible model, introducing additional complexities and sophistication later if necessary. I gave a possible evolution of the Earth leading to a solid mantle and inner core with a liquid outer core in 1953 based on two assumptions1. First, the mantle consists of silicates and the core of pure iron; second, in the core, the adiabatic temperature gradient is less than the melting point gradient. Higgins and Kennedy2 re-estimated these gradients and found that in the outer core the adiabatic gradient was steeper than the melting point gradient, that is, my second assumption was not satisfied. If the actual temperature followed the adiabatic temperature of ref. 2 the outer core would also be solid. They thus concluded that the actual temperature gradient is much less than the adiabatic gradient in the outer core which would then be thermally stably stratified, thereby inhibiting radial convection which is necessary to drive the geomagnetic dynamo.