Here's why:

* Plate Tectonics: The Earth's outer layer is made up of massive plates that move slowly over time.

* Divergent Boundaries: At mid-ocean ridges, two plates are moving apart from each other.

* Magma Upwelling: This separation allows magma (molten rock) from the Earth's mantle to rise to the surface.

* New Crust Formation: As the magma cools and solidifies, it creates new oceanic crust, pushing the plates further apart.

This process is known as sea floor spreading. It's a continuous process that helps create new ocean floor and contributes to the movement of the continents.