Sea-Floor Spreading

In the middle of the Atlantic ocean is a submerged mountain range called a mid-ocean ridge. It is part of a worldwide system of mid-ocean ridges formed by sea-floor spreading.

Sea-floor spreading occurs when two tectonic plates pull away from each other, and a crack forms in the ocean floor. Magma from the Earth's mantle pours onto the ocean floor through the crack and creates new oceanic crust.

A mid-ocean ridge is formed along the crack where magma is emerging. As the sea floor spreads, new oceanic crust pushes the older crust away from the ridge.

Sea-floor spreading is part of the plate tectonics theory. In the Atlantic, the plates move away from the mid-ocean ridge at a rate of about one centimeter per year. As the sea floor spreads, the Earth's crust is changing and moving the continents as well.