Magma heats nearby rocks and underground aquifers. Magma exists in the mantle and lower crust, and sometimes bubbles to the surface as lava. If underground rock formations are heated to about 700-1,300° C (1,300-2,400° F), they can become magma. Magma is molten (partly melted) rock permeated by gas and gas bubbles. In most parts of the world, the geothermal gradient is about 25° C per 1 kilometer of depth (1° F per 77 feet of depth). This gradual change in temperature is known as the geothermal gradient. Heat from the core is constantly radiating outward and warming rocks, water, gas, and other geological material.Įarth’s temperature rises with depth from the surface to the core. Temperatures there rise to more than 5,000° Celsius (about 9,000° Fahrenheit). Radioactive decay is a continual process in the core. Potassium-40 most often decays to isotopes of calcium (calcium-40) and argon (argon-40). As potassium-40 decays, its nucleus changes, emitting enormous amounts of energy (radiation). Potassium, for instance, has 20 neutrons in its nucleus. Isotopes are forms of an element that have a different number of neutrons than regular versions of the element’s atom. However, the vast majority of Earth’s heat is constantly generated by the decay of radioactive isotopes, such as potassium-40 and thorium-232. A small portion of the core’s heat comes from the friction and gravitational pull formed when Earth was created more than 4 billion years ago. ( Geo means “earth,” and thermal means “heat” in Greek.) It is a renewable resource that can be harvested for human use.Ībout 2,900 kilometers (1,800 miles) below the Earth’s crust, or surface, is the hottest part of our planet: the core. Geothermal energy is heat that is generated within the Earth.
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