By then the Earth's molten interior had begun to settle into its current layer cake form: a dense, solid inner core surrounded by an outer liquid core — both rich in iron and metals such as gold, platinum, ruthenium and others that tend to form alloys with iron. (sciencenews.org)
Deep inside Earth, slow - motion convection of rocky minerals in the mantle and heat loss from the cooling solid inner core cause convection in the liquid outer core. (discovermagazine.com)
One side of Earth's solid inner core grows slightly while the other half melts. (newscientist.com)