The origin and chemical composition of the earth's core

Abstract

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 sim||pre|129 Xe produced from the extinct radioactivity of sim||pre|129 I with a half life of 17.6 × 10 6 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 sim||pre|40 K radioactive heat production in the liquid core, estimated at about 10 19 erg/s at the present time. This energy is more than adequate to produce convective motions in the outer core to generate the geomagnetic field.