* Plate Tectonics: The Earth's crust is constantly moving and interacting through a process called plate tectonics.

* Seafloor Spreading: At mid-ocean ridges, new oceanic crust is formed as magma rises from the Earth's mantle and cools. This process pushes older oceanic crust away from the ridge, creating a continuous "conveyor belt" of new crust.

* Subduction: Oceanic crust is denser than continental crust. When they collide, the oceanic crust gets pushed beneath the continental crust in a process called subduction. This process recycles the older oceanic crust back into the mantle.

Therefore, because ocean crust is constantly being created and recycled, it is much younger than the ancient continental crust.