Here's why:

* Divergent Plate Boundaries: These are areas where tectonic plates are moving apart. As the plates pull away from each other, magma from the Earth's mantle rises to the surface and cools, forming new crust. This process is called seafloor spreading.

Examples of where new crust forms:

* Mid-ocean ridges: These are underwater mountain ranges where new oceanic crust is constantly being formed.

* Rift valleys: These are areas on continents where the crust is being pulled apart, leading to the formation of new crust.

Let me know if you'd like more details about the process of seafloor spreading!