Double disk dynamos exhibit irregular magnetic polarity reversals. B. Energy sources for driving convection in the outer core. Radioactivity from 40 K, which is the most likely radiogenic element from solar abundances to reside in the Earth's core, but not likely to be in a liquid iron solution at core pressure. Compositional convection, in which heavier iron crystallizes out of solution onto the inner core boundary, i.e., the inner core is growing. Lighter residual element buoyantly rises.
Latent heat is released as the inner core material crystallizes.
A key test of this hypothesis depends on results from high pressure mineral physics, predicting the density of iron at inner core pressures and temperatures, and from seismology, measuring with high accuracy the amplitude of PKiKP waves reflected from the inner core to determine the density contrast at that boundary.