Geothermal energy is cost effective, completely sustainable, and emits virtually no pollution. Because geothermal energy is generated by the internal warmth of the Earth, and is "direct use," its source is endlessly replenishable, and does not have to be transformed before being utilized as energy. Heat from the Earth can simply be used as heat directly, rather than most energy sources, which are often transformed before reaching their intended use.
Geothermal energy comes from the heat stored within the Earth's mantle. The heat from this mantle radiates outward through the planet's thin crust. This can usually be accessed only a dozen or so feet beneath the surface itself. Humans have taken advantage of geothermal energy for a long time, like cellars or early shelters built within the ground itself. Root cellars were used to store food and vegetables, since the temperatures there never fell below freezing and were always cooler than the hottest days of summer.
