From the actual transcript of the show mentioned, Al Gore said:

"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 'cause the interior of the earth is extremely hot, several million degrees aces there are these incredibly hot rocks, , and the crust of the earth is hot ..."

Priceless.