Earth's crust

Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume.

It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper part of the mantle.

The temperature of the crust increases with depth,[2] reaching values typically in the range from about 700 °C (1,292 °F) to 1,600 °C (2,910 °F) at the boundary with the underlying mantle.

It formed via accretion, where planetesimals and other smaller rocky bodies collided and stuck, gradually growing into a planet.

This process generated an enormous amount of heat, which caused early Earth to melt completely.

None of Earth's primary crust has survived to today; all was destroyed by erosion, impacts, and plate tectonics over the past several billion years.

Consequently, old crust must be destroyed, so opposite a spreading center, there is usually a subduction zone: a trench where an ocean plate is sinking back into the mantle.

The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4.28 billion years [18][19] and have been found in the Narryer Gneiss terrane in Western Australia, in the Acasta Gneiss in the Northwest Territories on the Canadian Shield, and on other cratonic regions such as those on the Fennoscandian Shield.