Heat Sources in the EarthYou know already, from our previous discussion, that the Earth's interior is hot -- indeed, the deep core of the Earth is hotter than the face of the sun. Students often assume that this is because the material down there is under such enormous pressure. This is actually not correct. If left on its own for long enough, the Earth would eventually lose all its interior heat and become stone cold, but the central pressure, caused by the inward pull of gravity and the tremendous weight of the overlying layers, would persist.In short, the presence of high pressure alone does not necesarily imply heat. But the two are closely related. Think back to the formation of the Earth, with particles, pebbles, and planetesimals colliding and coalescing to build up a larger and larger planet. The conversion of potential energy to kinetic (infall) energy to thermal energy (on impact) yields heat, and the buildup
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radioactive elements, small cometary bodies, occasional hyperenergetic collisions, deep interior