Here's why:

* Continental crust is thicker and less dense than oceanic crust. It forms the landmasses we see on Earth.

* Oceanic crust is thinner and denser than continental crust. It forms the ocean floor.

Tectonic plates are large pieces of Earth's lithosphere, which is the rigid outer layer of the planet. This lithosphere includes both the crust and the uppermost part of the mantle. So, a single tectonic plate can have both continental and oceanic crust on it.

For example, the North American plate includes both the North American continent and a large portion of the Atlantic Ocean floor.

Let me know if you'd like to know more about the different types of tectonic plates or the processes that drive their movement!