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 crust
- primordial 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.
