Geothermal energy comes from steam (or hot water that has been converted to steam) from deep inside the earth. The word “geothermal” comes from the Greek words geo, for earth, and therme, for heat. So geothermal means “earth heat.” Our planet’s interior is very hot—at its core, 4,000 miles deep, temperatures may reach over 9,000° F. This heat is continuously conducted from the earth’s core to the surrounding layer of rock, the mantle.
There are some places around the earth where magma (hot molten earth from the mantle) pushes up through cracks into the crust near the earth’s surface. Magma can heat nearby rock and water as hot as 700° F. Some of this hot water reaches the earth’s surface as hot springs or geysers, and some stays trapped deep underground in cracks and porous rocks. This hot water can be used directly or converted into steam to turn turbines that generate electricity at geothermal power plants.