Geothermal energy — using the natural heat beneath the Earth’s surface to generate electricity — is a vast, largely untapped resource with the potential to meet the nation’s power needs many times over. Today, two-thirds of the electricity generated in the U.S. comes from fossil fuels, including 39 percent from coal. Geothermal energy offers one of the most promising alternatives to fossil fuels for reducing carbon dioxide emissions while providing a stable baseload energy supply. It is renewable, has a small environmental footprint and emits no greenhouse gases.