Energy from sources other than fossil and nuclear fuels is, to a large extent, free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. This free course, Understanding deep geothermal energy, considers one of these alternative sources, geothermal energy, derived from the interior heat of the Earth, and the potential for this alternative to supplant fossil and nuclear fuel to power social needs fast enough to avoid the likelihood of future global warming and other kinds of pollution.