Here's why:

* Crust: The Earth's outermost layer, composed of relatively light, solid rock. It's divided into oceanic crust (thinner) and continental crust (thicker).

* Lithosphere: A rigid, outermost layer of the Earth that includes the crust and the uppermost part of the mantle. It behaves as a solid, but can be broken into tectonic plates that move.

Therefore, the lithosphere encompasses the crust and extends down into the upper mantle, making it significantly thicker than the crust alone.