View source for Geothermal gradient

[[Category:Done 2018-12-10]] 
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[[File:Blender3D_EarthQuarterCut.jpg|thumb|300px|Figure 1. The Earth gets hotter as one travels towards the core, known as the geothermal gradient.<ref>Wikimedia Commons [Online], Available: https://commons.wikimedia.org/wiki/File:Blender3D_EarthQuarterCut.jpg</ref>]]

<onlyinclude>The '''geothermal gradient''' is the amount that the Earth’s [[temperature]] increases with depth. It indicates [[heat]] ﬂowing from the Earth’s [[cross section of the Earth|warm interior]] to its surface.</onlyinclude><ref name=IPCC_SRREN> Verbruggen, A., W. Moomaw, J. Nyboer, 2011: Annex I: Glossary, Acronyms, Chemical Symbols and Preﬁxes. In IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation [O. Edenhofer, R. Pichs- Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer, C. von Stechow (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.</ref> '''On average''', the temperature increases by about '''[[celsius|25°C]]''' for every [[kilometer]] of depth.<ref name=wolf>R. Wolfson, "Energy from Earth and Moon" in ''Energy, Environment, and Climate'', 2nd ed., New York, NY: W.W. Norton & Company, 2012, ch. 8, pp. 204-224</ref> This difference in temperatures drives the flow of [[geothermal energy]] and allows humans to use this energy for [[geothermal district heating|heating]] and [[geothermal electricity|electricity generation]]. There are a number of places on the planet where the temperature changes quite a bit faster though, and those locations are almost always where [[geothermal energy]] is the most viable.

The [[cross section of the Earth|interior of the Earth]] is extremely hot, and reaches [[temperature]]s over [[celsius|5000°C]] near the core, which is not much colder than the surface of the [[Sun]] (the [[Nuclear fusion in the Sun|interior of the sun]] however is ''much'' hotter).<ref>D. Alfè; M. Gillan & G. D. Price (January 30, 2002). "Composition and temperature of the Earth's core constrained by combining ab initio calculations and seismic data" (PDF). Earth and Planetary Science Letters (Elsevier) 195 (1–2): 91–98. Bibcode:2002E&PSL.195...91A. doi:10.1016/S0012-821X(01)00568-4.</ref>

==Where is the heat from?==

It was discovered in the early 20th century that the Earth's underground heat is from [[radioactive]] elements. Specifically, geothermal heating is caused by the [[radioactive decay|decay]] of [[element]]s such as [[potassium]], [[uranium]] and [[thorium]]. These elements are not found in the core however, with the most popular model suggesting that they are found in the '''lithosphere''' and '''mantle'''. This form of heating is said to account for 50% of the Earth's heat, with the other heat coming from the primordial heat of the Earth (heat from the Earth's formation that has been trapped in the planet).<ref>Physics World. (2011). ''Radioactive decay accounts for half of Earth's heat'' [Online] Available:  http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decay-accounts-for-half-of-earths-heat</ref>

Figures 2 and 3 below shows how temperature decreases as it approaches Earth's surface, along with the mechanisms of heat flow. Overall, temperature changes are gradual except near the base of the mantle where drastic compositional changes occur, and in the lithosphere where the presence of fluids has a large effect. 

<gallery mode="packed" caption="Earth's Temperature Gradient" widths="250px" heights="320px" >
File:Temperature_schematic_of_inner_Earth.jpg|Figure 2. Temperature profile of the Earth's layers. Temperature increases with depth.<ref>Wikimedia Commons [Online], Available: https://commons.wikimedia.org/wiki/File:Temperature_schematic_of_inner_Earth.jpg#/media/File:Temperature_schematic_of_inner_Earth.jpg</ref>
File:Heat_flow_of_the_inner_earth.jpg|Figure 3. Heat transfer mechanisms within the Earth, along with the % amount of heat flow in each layer.<Ref>Wikimedia Commons [Online], Available: https://commons.wikimedia.org/wiki/File:Heat_flow_of_the_inner_earth.jpg#/media/File:Heat_flow_of_the_inner_earth.jpg</ref>
</gallery>

==For Further Reading== 
*[[Geothermal electricity]]
*[[Geothermal energy]]
*[[Ground source heat pump]]
*[[Geothermal district heating]]
*Or explore a [[Special:Random|random page]]

==References==
{{Reflist}}[[Category:Uploaded]]