<P> Earth 's internal heat budget is fundamental to the thermal history of the Earth . The flow of heat from Earth 's interior to the surface is estimated at 47 terawatts ( TW ) and comes from two main sources in roughly equal amounts : the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust , and the primordial heat left over from the formation of the Earth . </P>
where does earth 's internal heat come from
the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust the primordial heat left over from the formation of the Earth