The oceanic crust is the outermost layer of the Earth's surface found beneath the oceans. It is primarily composed of basalt, a dense volcanic rock, and is generally thinner than the continental crust, averaging about 5 to 10 kilometers in thickness. The oceanic crust is formed at mid-ocean ridges through volcanic activity and is continuously being created and destroyed through tectonic processes. This crust is younger than the continental crust, with most of it being less than 200 million years old. It plays a crucial role in the Earth's geology, influencing ocean currents and the formation of ocean basins. The subduction zones are areas where the oceanic crust can sink back into the mantle, leading to geological phenomena such as earthquakes and volcanic eruptions.