Here's why:

* Divergent Plate Boundaries: These are areas where tectonic plates are moving apart.

* Magma Upwelling: As plates pull away, the gap created allows magma from the Earth's mantle to rise to the surface.

* New Crust Formation: This magma cools and solidifies, forming new oceanic crust, which pushes the plates further apart.

* Mid-Ocean Ridge Creation: This continuous process of magma upwelling and new crust formation builds up underwater mountain ranges called mid-ocean ridges.

So, the process of plate divergence is the key factor in the formation of mid-ocean ridges.