Here's why:

* Constant Motion: Tectonic plates are huge slabs of Earth's crust and upper mantle that are constantly moving, driven by heat from the Earth's core. This movement is known as plate tectonics.

* Change the Forms of Crust: The movement of tectonic plates causes a variety of geological phenomena that change the forms of the Earth's crust. These include:

* Volcanoes: When plates collide or separate, magma rises to the surface, creating volcanoes.

* Earthquakes: The movement of plates along fault lines causes earthquakes.

* Mountain Ranges: When plates collide, they can push up mountains.

* Ocean Basins: When plates separate, new ocean floor is created.

Let me know if you'd like to learn more about any of these processes!