Here's why:

* Crust: The Earth's crust is the outermost layer, composed of solid rock. This is where we see the landforms that are directly affected by erosion and weathering.

* Erosion: The process of moving weathered material from one place to another (like wind blowing sand or water carrying away soil).

* Weathering: The breakdown of rocks, soil, and minerals through physical and chemical processes (like freezing water cracking rocks or acid rain dissolving limestone).

While the other layers of the Earth (mantle and core) are also involved in geological processes, they are not directly exposed to the forces that drive erosion and weathering.