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this answer is similar:… to what you might want, though not exactly – Neo May 4 '14 at 17:53
I understand "cooking" as "phase transition from liquid to gas". Is that what you mean? – BHF May 4 '14 at 18:13
I took the title question figuratively, interpreting it as if the title was "What keeps the center of the Earth so blazin' hot?" Cooking is just a figure of speech. – David Hammen May 4 '14 at 19:20
Please provide some reference to evidence that only half of Earth's heat flow can be explained by radioactive decay. I expect there's differing options about that. You stated it as if it were a fact. – Mark Rovetta May 4 '14 at 19:42
@BHF: David Hammen is correct, the use of "cooking" is figurative not literal; though to be clear, "cooking" does not even require heat, though that's more of a topic for Cooking.SE or English.SE. – blunders May 4 '14 at 20:39
up vote 6 down vote accepted

If radioactive decay supplies only about half the Earth’s heat, what are the remaining sources of heat?

Mostly it is residual heat energy from when the Earth was very young. The biggest source came from the kinetic energy of all the bodies, big and small, that collided to form the Earth being converted to heat. The differentiation of the Earth added even more heat energy to the Earth.

In addition to radioactive decay, the on-going freezing of the outer core material onto to the inner core adds a bit more heat to the system, but neither one compensates for heat transported through the mantle and crust and then out into space. Note that this heating from below is but a tiny portion of the overall energy budget for the Earth's surface.

Even the Earth's surface was very hot shortly after the formation and differentiation of the Earth. While the surface cooled quickly (geologically speaking), the interior has not. The key reason is that 2,890 km of rock makes for a fairly thick blanket.

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This is an exciting topic of geophysics, because Earth's heat flow represents a classic question for earth science, heat source distribution is critical to modeling mantle convection, and because the application of geoneutrinos is cutting-edge experimental physics. The original publication reporting the use of KamLAND geoneutrino data was in Nature, and well worth reading. An online pdf is available here:

Partial radiogenic heat model for Earth revealed by geoneutrino measurements

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