Oceanic Crust   The uppermost layer of the earth beneath the ocean basins. Oceanic crust is constantly forming at mid-ocean ridges and is constantly being destroyed at subduction zones, thus the oldest oceanic crust on the earth is about 160 million years old. Oceanic crust is composed of basalt and is 5-7 km thick.

Used in the following modules: Earth Structure, Plate Tectonics II