Earth's internal heat budget

[3] It drives mantle convection, plate tectonics, mountain building, rock metamorphism, and volcanism.

[2] Convective heat transfer within the planet's high-temperature metallic core is also theorized to sustain a geodynamo which generates Earth's magnetic field.

This renders solar radiation minimally relevant for processes internal to Earth's crust.

Contrary to the usual representation of Thomson's argument, the observed thermal gradient of the Earth's crust would not be explained by the addition of radioactivity as a heat source.

More significantly, mantle convection alters how heat is transported within the Earth, invalidating Thomson's assumption of purely conductive cooling.

[18] Due to a lack of rock samples from below 200 km depth, it is difficult to determine precisely the radiogenic heat throughout the whole mantle,[18] although some estimates are available.

[19] For the Earth's core, geochemical studies indicate that it is unlikely to be a significant source of radiogenic heat due to an expected low concentration of radioactive elements partitioning into iron.

[22] However, due to the short half-lives the decay of 235U and 40K contributed a large fraction of radiogenic heat flux to the early Earth, which was also much hotter than at present.

[14] Initial results from measuring the geoneutrino products of radioactive decay from within the Earth, a proxy for radiogenic heat, yielded a new estimate of half of the total Earth internal heat source being radiogenic,[22] and this is consistent with previous estimates.

Global map of the flux of heat, in mW/m 2 , from Earth's interior to the surface. [ 1 ] The largest values of heat flux coincide with mid-ocean ridges , and the smallest values of heat flux occur in stable continental interiors.
Cross section of the Earth showing its main divisions and their approximate contributions to Earth's total internal heat flow to the surface, and the dominant heat transport mechanisms within Earth
The evolution of Earth's radiogenic heat flow over time
Earth's tectonic evolution over time from a molten state at 4.5 Ga, [ 11 ] to a single-plate lithosphere, [ 24 ] to modern plate tectonics sometime between 3.2  Ga [ 25 ] and 1.0 Ga [ 26 ]