The current theory of the earth's core is that it is composed on metallic iron and nickel. The question I have is, with the amount of oxygen present in the mantle and on the surface of the earth, i.e., water, oxides, ionized oxygen, etc., where did the reduction potential come from to allow so much metallic iron to phase separate from the other atoms?
In other words, if one took the average composition of the earth and heated and pressured it, the iron would not phase separate without a very significant source of reduction potential. We could add maybe carbon or hydrogen to iron/oxygen and make metallic iron. The early earth would have needed a very high concentration of hydrogen, carbon, etc., to allow an iron core. Yet there is not enough carbon plus hydrogen within the earth to account for the size of the iron core.