crustcontinentaloceanicmantle,core

lithosphereasthenospheretransitionmesospherelower mantleouter coreinner core

Earth's crustMohorovičić (Moho) discontinuity.

Oceanic crust2

Oceanic crust is young relative to the age of the Earth (~4.55 Ga = 4550 Ma). The oldest ocean crust in the major ocean basins, less than 190 million years old (190 Ma), occurs along the western and eastern borders of the Atlantic Ocean and in the Western Pacific Ocean. Recently, still older oceanic crust that may be 340 Ma has been discovered in the eastern Mediterranean Sea (Granot 2016). Still older oceanic crust has largely been destroyed by subduction, but fragments of such crust are preserved on land in the form of ophiolites. Ophiolites contain slices of ocean crust thrust onto continental margins and provide evidence for the existence of Precambrian oceanic crust. The age of the oldest true ophiolites of Precambrian age remains controversial (ssss1).