<Li> Erosion and sedimentation: sediments derived from primary, secondary, or tertiary crust </Li> <P> The only known example of tertiary crust is the continental crust of the Earth . It is unknown whether other terrestrial planets can be said to have tertiary crust, though the evidence so far suggests that they do not . This is likely because plate tectonics is needed to create tertiary crust, and Earth is the only planet in our Solar System with plate tectonics . </P> <P> The crust is a thin shell on the outside of the Earth, accounting for less than 1% of Earth's volume . It is the top component of 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 that move, allowing heat to escape from the interior of the Earth into space . </P> <P> The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is 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 . </P>

What is the purpose of the earths crust