Page - 135 - in Water, Energy, and Environment - A Primer

8.6.2 Manifestationsofgeothermalenergy Initially, the core of theEarthwas a hot liquid but it has cooled over geological time, and the core is now seen as an anisotopic high-temperaturemass of solid iron created under conditions of extremelyhighpressure. Somewhat above the core some rock is stillmolten, formingmagmawhich convects upwards since it is lighter than rock. Themagma heats rock andwater in the crust, creating hot water and steam at various points on and near the Earth’s surface. It is estimated that the amount of heat in hot rock and water within 6 miles of the Earth’s surface is more than 50,000 times as much as all the energy stored in the planet’s oil andnatural gas resources. 8.6.3 Usesofgeothermalenergy Howhasthisheatbeenusedinthepast,howisitbeingusedtoday, andhowmight it be used in the future?Historically, hot springs have been used for bathing by humans since the StoneAge and Figure8.14 Schematic crosssectionof theEarth. Renewableenergy 135