ScienceDaily (July 17, 2011) — What spreads the sea floors and moves the continents? What melts iron in the outer core and enables Earth's magnetic field? Heat. Geologists have used temperature measurements from more than 20,000 boreholes around the world to estimate that some 44 terawatts (44 trillion watts) of heat continually flow from Earth's interior into space. Where does it come from?
http://www.sciencedaily.com/releases/2011/07/110717134819.htm