Animation of the internal structure of the Earth, showing the crust opened in the North Atlantic Ocean. Inside the Earth, convection of liquid rock in the mantle drives the movements of overlying tectonic plates. The Atlantic Ocean is bisected by the Mid-Atlantic Ridge, a long fault running north-south, along which new crust is formed by the eruption of magma from the underlying layers. The formation of the new crust means that the North American and Eurasian plates are constantly moving apart. At the other side of the plates, the plates subduct under neighbouring plates, returning to the underlying mantle.