The very top of the Earth's mantle, combined with the Earth's crust, is called the lithosphere.

Here's a breakdown:

* Mantle: The layer of the Earth between the crust and the core. It's mostly solid rock, but it behaves like a very viscous fluid over long periods.

* Crust: The outermost layer of the Earth. It's relatively thin and composed of igneous, sedimentary, and metamorphic rocks.

* Lithosphere: The rigid, outermost layer of the Earth, encompassing the crust and the uppermost, solid portion of the mantle. It's broken into tectonic plates that move and interact, causing earthquakes and volcanic activity.

So, the lithosphere is essentially the solid, rocky outer shell of the Earth, formed by the combination of the crust and the topmost part of the mantle.