Editing Convection (section)

===Mantle convection===
{{main|Mantle convection}}
[[File:Accretion-Subduction.PNG|thumb|right|250px|An [[oceanic plate]] is added to by upwelling (left) and consumed at a [[subduction]] zone (right).]]

'''Mantle convection''' is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface.<ref name="University of Winnipeg">{{cite web | date = 2002-12-16 | last1 = Kobes | first1 = Randy | first2 = Gabor | last2 = Kunstatter | url = http://theory.uwinnipeg.ca/mod_tech/node195.html | title = Mantle Convection | publisher = Physics Department, University of Winnipeg | access-date = 2010-01-03 | url-status = dead | archive-url = https://web.archive.org/web/20110114151750/http://theory.uwinnipeg.ca/mod_tech/node195.html | archive-date = 2011-01-14 }}</ref> It is one of 3 driving forces that causes tectonic plates to move around the Earth's surface.<ref name=Condie>{{cite book |title=Plate tectonics and crustal evolution |first=Kent C. |last=Condie |url=https://books.google.com/books?id=HZrA6OQzsvgC&pg=PA5 |page=5 |isbn=978-0-7506-3386-4 |year=1997 |edition=4th |publisher=Butterworth-Heinemann |url-status=live |archive-url=https://web.archive.org/web/20131029161501/http://books.google.com/books?id=HZrA6OQzsvgC&pg=PA5 |archive-date=2013-10-29 }}</ref>

The Earth's surface is divided into a number of [[tectonic]] plates that are continuously being created and consumed at their opposite plate boundaries. Creation ([[Accretion (geology)|accretion]]) occurs as mantle is added to the growing edges of a plate. This hot added material cools down by conduction and convection of heat. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction at an ocean trench. This subducted material sinks to some depth in the Earth's interior where it is prohibited from sinking further. The subducted oceanic crust triggers volcanism.

Convection within [[Earth's mantle]] is the driving force for [[plate tectonics]]. Mantle convection is the result of a thermal gradient: the lower mantle is hotter than the [[upper mantle (Earth)|upper mantle]], and is therefore less dense. This sets up two primary types of instabilities. In the first type, plumes rise from the lower mantle, and corresponding unstable regions of [[lithosphere]] drip back into the mantle. In the second type, subducting oceanic plates (which largely constitute the upper thermal boundary layer of the mantle) plunge back into the mantle and move downwards towards the [[core-mantle boundary]]. Mantle convection occurs at rates of centimeters per year, and it takes on the order of hundreds of millions of years to complete a cycle of convection.

Neutrino flux measurements from the Earth's core (see [[kamLAND]]) show the source of about two-thirds of the heat in the inner core is the [[radioactive decay]] of [[potassium|<sup>40</sup>K]], uranium and thorium.  This has allowed plate tectonics on Earth to continue far longer than it would have if it were simply driven by heat left over from Earth's formation; or with heat produced from [[gravitational energy|gravitational potential energy]], as a result of physical rearrangement of denser portions of the Earth's interior toward the center of the planet (that is, a type of prolonged falling and settling).
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