Scientists are always looking for safe, practical, efficient, cheap forms of energy. One such form of energy may lie just a few miles below the earth's surface, and it's not oil, says Discover magazine.

The source of energy is the earth's mantle, which is as close as six miles to the earth's surface. The mantle still retains residual heat from the creation of the planet.This potentially limitless source of energy could be tapped by a heat exchanging system. Over the next four years, a geological team will drill an exploratory well in Long Valley Caldera Water would then be pumped down and returned to the surface as either steam or superheated water. It would be used to drive turbines to produce electricity.