Geothermal (main)
From The Encyclopedia of Earth
Geothermal
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Geothermal Electric Power PlantsTemperatures from the surface to the center of the Earth warm by 17° to 30°C for every kilometer in depth, reaching 5100°C in the inner core (nearly the temperature... More »
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Geothermal Electric Power Plants Last Updated on 2010-11-25 00:00:00 Temperatures from the surface to the center of the Earth warm by 17° to 30°C for every kilometer in depth, reaching 5100°C in the inner core (nearly the temperature of the sun). [1] The energy that heats Earth’s interior derives from several sources. First is the decay of radioactive isotopes, especially 238uranium, 235uranium, 232thorium, and 40potassium. Second, because the Earth first formed regardless of density, heavy metals (like iron, nickel, and copper) are continually sinking towards the center of the Earth, displacing lighter elements (like aluminum, sulfur, and silicon), creating friction and heat. Third, the Earth’s interior still retains some of the energy from its formation 4.5 billion years ago. Earth’s crust varies in thickness from about 5 km to 75 km. Locations with thinner crust, such as at boundaries of tectonic plates, fault... More » 
