How did the inner core nucleate without implausible supercooling?

Classical homogeneous nucleation of hcp Fe at the center requires supercooling of order 1000 K, whereas thermal histories permit at most a few hundred K. Identify a pathway (metastable bcc two-step nucleation, Ni, C, Si or O effects on the liquid, heterogeneous seeds) that yields at least one critical nucleus in the core volume within about 1 Gyr at supercooling consistent with thermal models. An answer is a computed nucleation rate versus supercooling for a realistic core composition.

Molecular dynamics or free-energy calculations of nucleation rates for realistic Fe alloys at inner-core-boundary pressure, reproducing an allowed supercooling.