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Craton: Cores of Continents

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December 27, 2012 in Offbeat

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The Foundation of Continents:

“A craton (Greek: κράτος kratos “strength”) is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by younger sedimentary rock. They have a thick crust and deep lithospheric roots that extend as much as a few hundred kilometers into the Earth’s mantle.

The term craton is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons can be described as shields, in which the basement rock crops out at the surface, and platforms, in which the basement is overlain by sediments and sedimentary rock.”

“Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice the typical 60-mile (100 km) thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic isopycnic density. This low density offsets density increases due to geothermal contraction and prevents the craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years.”

“The process by which cratons are formed from early rock is called cratonization. The first large cratonic landmasses formed during the Archean eon. During the Early Archean, Earth’s heat flow was nearly three times higher than it is today because of the greater concentration of radioactive isotopes and the residual heat from the Earth’s accretion.”

en.wikipedia.org

 

“During the Early Archean, Earth’s heat flow was nearly three times higher than it is today”
 

“Io is the most geologically active body in the Solar System, and though it is less than a third of Earth’s size, it generates twice as much heat as the Earth.”

NASA.gov

 

“Archean Eon, also spelled Archaean Eon, [Credit: Encyclopædia Britannica] the earlier of the two divisions of Precambrian time (about 4 billion to 542 million years ago). The Archean Eon began about 4 billion years ago with the formation of the Earth’s crust and extended to the start of the Proterozoic Eon 2.5 billion years ago; the latter is the second division of Precambrian time.”
 

4 billion years ago = Io #1 Proto-Earth

*Original Astronomical Planet Infowars Discovery


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