The internal heat of the planet is from a combination residual heat from planetary accretion (20%) and heat produced through radioactive decay (80%).[60] The major heat-producing isotopes in the Earth are potassium-40, uranium-238, uranium-235, and thorium-232.[61] At the center of the planet, the temperature may be up to 7,000 K and the pressure could reach 360 GPa.[62] Because much of the heat is provided by radioactive decay, scientists believe that early in Earth 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 billion years ago,[60] would have increased temperature gradients within the 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.[63]
| Isotope | Heat release [W/kg isotope] | Half-life [years] | Mean mantle concentration [kg isotpoe/kg mantle] | Heat release [W/kg mantle] |
|---|---|---|---|---|
| 238U | 9.46 × 10-5 | 4.47 × 109 | 30.8 × 10-9 | 2.91 × 10-12 |
| 235U | 5.69 × 10-4 | 7.04 × 108 | 0.22 × 10-9 | 1.25 × 10-13 |
| 232Th | 2.64 × 10-5 | 1.40 × 1010 | 124 × 10-9 | 3.27 × 10-12 |
| 40K | 2.92 × 10-5 | 1.25 × 109 | 36.9 × 10-9 | 1.08 × 10-12 |
Total heat loss from the earth is 4.2 × 1013 Watts.[65] 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.[66] More of the heat in the 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, majority of which occurs in the oceans due to the crust there being much thinner than that of the continents.[65]
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