Here's why:
* Separation: The plates move apart, creating a gap.
* Magma Upwelling: Magma from the Earth's mantle rises to fill the gap.
* New Crust Formation: The magma cools and solidifies, creating new oceanic crust.
* Ridge Formation: Over time, the process of magma upwelling and crust formation builds up a long, underwater mountain range called a mid-ocean ridge.
These ridges are often marked by:
* Volcanic Activity: Active volcanoes along the ridge create new crust.
* Hydrothermal Vents: Hot springs called hydrothermal vents release chemicals and heat from the Earth's interior.
* Shallow Earthquakes: The separation of the plates causes frequent, shallow earthquakes.
The Mid-Atlantic Ridge is a classic example of a mid-ocean ridge formed at a divergent boundary between the North American and Eurasian plates.
