It's important to note that the lithosphere isn't just the mantle. It includes the crust (the outermost layer of Earth) and the uppermost, rigid part of the mantle. This entire rigid layer is what makes up the tectonic plates that move across the Earth's surface.

Here's a breakdown:

* Crust: The outermost layer, thin and brittle, made up of oceanic and continental crust.

* Lithosphere: Includes the crust and the uppermost, rigid portion of the mantle. This layer is about 100 km thick and is broken into tectonic plates.

* Asthenosphere: The layer beneath the lithosphere. It is semi-molten and is where the tectonic plates move.

So, while the lithosphere is the uppermost layer of the mantle, it is more accurately described as the uppermost layer of the Earth, including the crust.