Geothermal energy or earth heat has the potential of becoming the foremost source of energy during the next few decades just as the fossil fuels have been for the past 75 years. This source is so great that it is limitless, unlike the fossil or nuclear fission fuels. Yet there are formidable problems in the application of geothermal energy for useful work.
Turner, George M., "Energy in Agriculture: Energy Resource Series for Youth and Adult Energy Programs: 11. Geothermal" (1981). Agricultural Engineering Energy Series. 6.