What are two sources of heat in the earths interior

The flow of heat from Earth's interior to the surface is estimated at terawatts (TW) and comes from two main sources in roughly equal amounts:

radiogenic heat produced by the radioactive decay of isotopes in the mantle and crustprimordial heat left over from the formation of the Earth.                                                                        The other main sources of heat in the deep earth are:Heat from when the planet formed and accreted, which has not yet been lost; Frictional heating, caused by denser core material sinking to the center of the planet Heat from the decay of radioactive elements.

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