Roland Piquepaille writes: "When we think about alternative sources of energy, we often forget the potential of geothermal energy resources. In fact, it has been estimated that accessible geothermal energy in the U.S. represents 90 quadrillion kilowatt-hours or 3,000 times the country's total annual energy consumption. So far, it has been difficult and expensive to locate good sources of geothermal energy. But now, two U.S. researchers have found a new method which doesn't require drilling. They are using the ratio of helium isotopes in surface waters to point to the best sources of geothermal energy. But read more for additional references and a picture showing how sampling surface water can lead to new sources of geothermal energy."