The part of the Earth's structure that is about 100 km thick is the crust.

There are two types of crust:

* Oceanic crust: This is thinner, about 5-10 km thick, and is composed mainly of basalt and gabbro.

* Continental crust: This is thicker, ranging from 30 to 70 km, and is composed mainly of granite and other felsic rocks.

While the average thickness of the crust is around 100 km, it varies significantly depending on location and type.