A theory of the origin of the Earth's internal heat

Abstract

A gravitational source of heat is added to secular cooling and the heat from the decay of radioactive elements to close the gap between heat loss and heat production for whole mantle convection. This unrecognized source of heat comes from viscous friction in sheet-like mantle plumes rising from the core-mantle boundary to create oceanic plates, cause earthquakes and raise mountains and volcanoes. The frictional heat generated in the plumes is equal to the gravitational potential energy lost because their heavy fraction, FeO, was absorbed by the molten iron at the top of the core. When mantle material is subjected to the temperature and pressure prevailing at the 670 km seismic discontinuity in the laser-heated diamond cell, it is transformed into a magnesium iron silicate perovskite and magnesiowuestite that remain stable to the temperature and pressure of the core-mantle boundary, where they lose their FeO to the core. The energy that had been expended by this process during the life of the Earth, has come from the composition Fe 2O of the outer core, as required by the seismic speeds and the moment of inertia of the Earth. This energy is 7.07 × 10 30 J, 2.3 times what would have been expended by plate creation at the present rate. Secular cooling does not originate from the primordial high temperature, but from the decay of the radioactivity and the decrease of the amount of FeO in the mantle (Schubert et al., 1980). At present plate creation by mantle plumes provides 47.5% of the heat of 44.2 TW. The larger part of this heat comes from viscous friction in the plumes, the remainder coming from the cooling of the core. Radioactivity gives 41%, and 11% comes from secular cooling that takes no part in plate creation. In apportioning the heat from these sources between land and sea, it is assumed that in very old oceans only 15% of the heat comes from plate creation and that the remaining 85% comes from radioactive elements uniformly disseminated in the mantle and secular cooling. The last two sources being world-wide, we extend this heat of 32.0 mW/m 2 over the 510 × 10 6 km 2 of the Earth's surface, 16.3 TW in all. At sea, where the heat flow is greater than 32.0 mW/m 2, the additional heat comes from plate creation, while on land the extra amount is from radionuclides concentrated in the crust. The measured losses on land and sea are 30% and 70% of 44.2 TW, respectively. On land, the total measured loss is 13.26 TW, 86% of it is radiogenic, and 14% is from cooling. At sea, the heat loss is 30.9 TW, 22% of it is radiogenic, 10% from cooling and 68% from plate creation. Table 2 lists the measured and computed quantities.