Here's why:

* Divergent Plate Boundaries: At these boundaries, two tectonic plates move apart.

* Magma Upwelling: As the plates separate, magma rises from the Earth's mantle to fill the gap. This magma cools and solidifies, forming new oceanic crust.

* Ocean Ridge Formation: This continuous process of magma upwelling and crust formation creates the underwater mountain ranges known as ocean ridges.

Therefore, ocean ridges are essentially the physical manifestation of divergent plate boundaries.