Oceanic crust is the outer layer of the Earth's surface that lies beneath the oceans. It is primarily composed of basalt, a dense volcanic rock, and is generally thinner than continental crust, averaging about 5 to 10 kilometers in thickness. The oceanic crust is formed at mid-ocean ridges, where tectonic plates pull apart, allowing magma to rise and solidify. This crust is constantly being created and destroyed through processes like seafloor spreading and subduction. As tectonic plates move, older sections of oceanic crust can sink back into the mantle at subduction zones, contributing to the dynamic nature of the Earth's geology.