The radioactive isotopes inside the Earth generate heat. In particular, decays of the daughter nuclei in the decay chains of uranium-238 and thorium-232, and potassium-40 generate most of the radiogenic heat produced. According to the estimated concentrations of these isotopes, the radiogenic heat production rates are 8.0, 8.3, and 3TW for the uranium-238 series, thorium-232 series, and potassium-40 decays, respectively. The sum of the estimated radiogenic heat production rate, ~19TW, is only about the half of the total heat flow measured using borehole measurements. According to some mantle convection models, these two numbers, 44TW (or 31TW) for the total heat dissipation rate from the Earth, and 19TW for radiogenic heat production rate should be similar.
As these radioactive isotopes beta-decay, they produce antineutrinos. So, measuring these antineutrinos may serve as a crosscheck of the radiogenic heat production-rate (image and text: Stanford University).
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