Seafloor spreading is a geologic process that occurs when tectonic plates—large slabs of Earth's lithosphere—split apart from one another.

The hypothesis is that oceanic crust emerges beneath submarine mountain zones, collectively known as the mid-ocean ridge system, and spreads out laterally away from each other. This concept was crucial in the development of plate tectonics theory, which transformed geologic research in the last part of the twentieth century.

Seafloor spreading takes place between mid-ocean ridges, which are huge mountain ranges that rise from the ocean floor. The East Pacific Rise, for one, is a mid-ocean ridge that divides the Pacific plate from the North American plate, the Cocos plate, the Nazca plate, and the Antarctic plate in the eastern Pacific Ocean.