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Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).[50] The major heat-producing isotopes in Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[51] At the center, the temperature may be up to 6,000 °C (10,830 °F),[52] and the pressure could reach 360 GPa.[53] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth's history, before isotopes with short half-lives had been depleted, Earth's heat production would have been much higher. This extra heat production, twice present-day at approximately 3 byr,[50] would have increased temperature gradients within Earth, increasing the rates of mantle convection and plate tectonics, and allowing the production of igneous rocks such as komatiites that are not formed today.[54] Present-day major heat-producing isotopes[55] The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42 × 1013 W.[56] A portion of the core's thermal energy is transported toward the crust by mantle plumes; a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts.[57] More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs in the oceans because the crust there is much thinner than that of the continents.[58] |
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