Found this article about some scientists that think the earth's inner core is actually a monstrous breeder reactor putting out millions of megawatts of power per day over the past 4.5 billion years. The theory explains all the wonky things that the earth's magnetic field has done over the years, like shut off and reverse polarity. And the theory's already passed a few experimental tests, so this is looking more and more solid (as it were). Extremely cool.