Earth's Interior is extremely hot
Al Gore, NBC "Tonight Show with Conan O'Brien, 12-11-2009.
O'BRIEN: ...Can you, can you tell me, is this a viable solution, geothermal energy?
GORE: It definitely is, and it's a relatively new one. People think about geothermal energy - when they think about it at all - in terms of the hot water bubbling up in some places, but two kilometers or so down in most places there are these incredibly hot rocks, 'cause the interior of the earth is extremely hot, several million degrees, and the crust of the earth is hot ...