Phys. Earth Planet. Inter.http://doi.org/htx (2012)

If the solid inner core cooled and grew slowly at the centre of a hot, early Earth, it should be homogeneous, an expectation not borne out by seismic waves that travel through it. Numerical models of the thermal and chemical history of the inner core indicate that an episode of thermal convection could explain seismic observations of heterogeneity.

Sanne Cottaar and Bruce Buffett at the University of California, Berkeley, assessed how the inner core would have evolved under a range of conditions using numerical models. The simulations showed that it is plausible that the early inner core was thermally unstable. This instability could have allowed convection at a range of cooling rates, especially in the early stages of core growth. Convection would persist longer if there was a period of rapid cooling during the initial stages of growth.

The termination of convection at an early stage of the core's evolution may explain the observed heterogeneity of the inner core. Furthermore, the weakening of convection over time could account for stronger heterogeneity in the innermost part of the inner core as compared with the outer regions.