Geochemical data show that radioactive heat production in the crust plus upper mantle (which is defined seismically to terminate at a depth of 415 km) cannot account for the heat escaping from the Earth. Deeper sources must be invoked, and a number of qualitative models of the variation of radioactive heat generation with depth are suggested. Preferred models involve a narrow zone of high heat production about halfway between the crust and the core.
INFLUENCE OF NON-RADIOGENIC COSMIC HEAT GENERATION IN THE BOWELS OF THE EARTH AND PLANETS ON MUTUAL DISPLACEMENTS OF PLANETARY SHELLS Article 1. The Earth