The origin and chemical composition of the earth's core

The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.