Geothermal_(geology)

For other uses see Geothermal (disambiguation)

Earth cutaway from core to exosphere. Partially to scale.

In geology, geothermal refers to heat sources within the planet. Strictly speaking, geo-thermal necessarily refers to the Earth but the concept may be applied to other planets.

Geothermal is technically an adjective (e.g., geothermal energy) but in U.S. English the word has attained frequent use as a noun (otherwise expressed as g. heat, g. source, or geotherm).

The planet\'s internal heat was originally generated during its accretion, due to gravitational binding energy, and since then additional heat has continued to be generated by the radioactive decay of elements such as uranium, thorium, and potassium. The heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the Sun.

Sources

Temperature within the Earth increases with increasing depth. Highly viscous or partially molten rock at temperatures between 1,200 and 2,200 °F (650 to 1,200 °C) is postulated to exist everywhere beneath the Earth\'s surface at depths of 50 to 60 miles (80 to 100 kilometers), and the temperature at the Earth\'s center, nearly 4,000 miles (6,400 kilometers) deep, is estimated to be 5650 ± 600 kelvins. Alfe, D.; M. J. Gillan, G. D. Price (2003-02-01). "Thermodynamics from first principles: temperature and composition of the Earths core" (PDF). Mineralogical Magazine 67 (1): 113-123. doi:10.1180/0026461026610089. Retrieved on 2007-03-01. Steinle-Neumann, Gerd; Lars Stixrude, Ronald Cohen. "New Understanding of Earth’s Inner Core", Carnegie Institution of Washington, 2001-09-05. Retrieved on 2007-03-01. 

• Much of the heat is believed to be created by decay of naturally radioactive elements. An estimated 45 to 90 percent of the heat escaping from the Earth originates from radioactive decay of elements within the mantle.Anuta, Joe. "Probing Question: What heats the earth\'s core?", physorg.com, 2006-03-30. Retrieved on 2007-09-19. 
• Heat of impact and compression released during the original formation of the Earth by accretion of in-falling meteorites.
• Heat released from the sinking of abundant heavy metals (iron, nickel, copper) as they descended to the Earth\'s core.
• Some heat may be created by electromagnetic effects of the magnetic fields involved in Earth\'s magnetic field.
• Heat generated within the Earth\'s core may be in the range of 4–10 TW. Hollenbach, D. F.; J. M. Herndon (2001-09-25). "Thermodynamics from first principles: temperature and composition of the Earths core". PNAS 98 (20): 11085-11090. doi:10.1073/pnas.201393998. Retrieved on 2007-03-01. 
• Heat may be generated by tidal force on the Earth as it rotates, since land cannot flow like water it compresses and distorts, generating heat.

Heat flow

Heat flows constantly from its sources within the Earth to the surface. Global terrestrial heat flow is about 45 TW (1 TW = 10¹² watts).

Hot spots

Geothermal heat at the surface is highly concentrated where magma is close to the surface. This primarily occurs in volcanic and hotspot areas and at spreading ridge areas.

References

Geothermal Resources. DOE/EIA-0603(95) Background Information and 1990 Baseline Data Initially Published in the Renewable Energy Annual 1995. Retrieved on May 4, 2005.

See also

• Geothermal power
• Hydrothermal circulation

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