THE ORIGIN OF TERRESTRIAL HEAT-FLOW

A theory of the origin of the Earth's heat which agrees with all observations is presented. The radiogenic heat production from the decay of U and Th was computed from their abundances in ordinary chondrites from which the Earth accreted and from the abundance of potassium in the mantle plus crust. The total radiogenic heat production is 1.14 x 10(13) W. Because U and Th are incompatible in the silicates, they have migrated upward into the continental rocks. The sediments eroded from the continents are returned to the continents on subducting oceanic slabs. Therefore, about 90 per cent of U and Th are concentrated in the continents. This is confirmed by a worldwide survey of helium in the oceans which found only 5 per cent of the helium that should have been there, had the heat come from radioactive decay. Subtracting the radiogenic heat production of 1.14 x 10(13) W from the total heat loss of 4.2 x 10(13) W, yields 3.06 x 10(13) W to be supplied by the non-radioactive sources in the mantle. It is proposed that non-radiogenic heat originates from secular cooling and from the release of gravitational potential energy by the absorption of FeO from the mantle into the core. This reaction has been produced in the laser-heated diamond anvil cell at temperatures and pressures of the core-mantle boundary layer. As the molten iron extracts most of the FeO out of the perovskite of the mantle, a light residue consisting of an iron-depleted perovskite and stishovite, a form of silica, rises in the form of plumes and megaliths generating heat by viscous friction. If the oxygen now present in the core got there by this process, 10(27) g of FeO have descended into the core, generating energy at an average rate of twice the present rate of loss of non-radiogenic heat. Adding the contribution of secular cooling, an average rate of non-radiogenic heat production of 10(14) W could have been sustained for the last 4.6 billion yr.