Here's why:

* Seafloor Spreading: Mid-ocean ridges are where new oceanic crust is formed. Magma rises from the Earth's mantle, cools, and solidifies, creating new crust. This process is called seafloor spreading.

* Continuous Creation: As the plates move apart, new crust is constantly being formed at the ridge.

* Age Gradient: As you move away from the ridge, the crust gets older. This is because the older crust is pushed further away from the ridge as new crust forms.

Therefore, the rock directly at the mid-ocean ridge is the youngest oceanic crust on Earth.