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Concept
Earth's crust
Summary
Earth's crust is Earth's thick outer shell of rock, referring to less than 1% of the Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The lithosphere is broken into tectonic plates whose motion allows heat to escape from the interior of the Earth into space.
The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and is therefore significantly denser than the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.
The temperature of the crust increases with depth, reaching values typically in the range from about to at the boundary with the underlying mantle. The temperature increases by as much as for every kilometer locally in the upper part of the crust.
Abundance of elements in Earth's crust and Goldschmidt classification
File:Elemental abundances.svg|Abundance (atom fraction) of the chemical elements in Earth's upper continental crust as a function of the atomic number.The rarest elements in the crust (shown in {{background color|#ffde54|yellow}}) are not the heaviest, but are rather the siderophile (iron-loving) elements in the [[Goldschmidt classification]] of elements. These have been depleted by being relocated deeper into Earth's core. Their abundance in [[meteoroid]] materials is higher. Additionally, tellurium and selenium have been depleted from the crust due to formation of volatile hydrides.
The crust of Earth is of two distinct types:
Oceanic: to thick and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.
Continental: to thick and mostly composed of less dense, more felsic rocks, such as granite. In a few places, such as the Tibetan Plateau, the Altiplano, and the eastern Baltic Shield, the continental crust is thicker ( to ).
The average thickness of the crust is about to .
Official source
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