Crust (geology)

The crusts of Earth, Mercury, Venus, Mars, Io, the Moon and other planetary bodies formed via igneous processes and were later modified by erosion, impact cratering, volcanism, and sedimentation.

[2] This crust was likely destroyed by large impacts and re-formed many times as the Era of Heavy Bombardment drew to a close.

[3] The nature of primary crust is still debated: its chemical, mineralogic, and physical properties are unknown, as are the igneous mechanisms that formed them.

[5] Like Earth, Venus lacks primary crust, as the entire planet has been repeatedly resurfaced and modified.

[8] Secondary crust is formed by partial melting of mostly silicate materials in the mantle, and so is usually basaltic in composition.

Most of the surfaces of Mercury, Venus, Earth, and Mars comprise secondary crust, as do the lunar maria.

On Earth secondary crust forms primarily at mid-ocean spreading centers, where the adiabatic rise of mantle causes partial melting.

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.

[9] The lithosphere is broken into tectonic plates that move, allowing heat to escape from the interior of Earth into space.

Study of the Moon has established that a crust can form on a rocky planetary body significantly smaller than Earth.