Which term describes the rigid layer of the Earth composed of the crust and upper mantle?

The term that describes the rigid layer of the Earth composed of the crust and upper mantle is "lithosphere." This layer is characterized by its solid and relatively rigid nature, which allows it to maintain structural integrity compared to the underlying layers. The lithosphere includes both the continental and oceanic crust as well as the uppermost part of the mantle, which together form the outer shell of the Earth.

In geological terms, the lithosphere is distinct from layers such as the asthenosphere, which lies just beneath it. The asthenosphere is more ductile and behaves plastically, allowing for the movement of tectonic plates that rest on the lithosphere. The mesosphere refers to the part of the mantle located beneath the asthenosphere, which is also more solid but under higher pressure and temperature conditions. The core, which consists of the outer and inner core, is a separate, much deeper layer composed mainly of iron and nickel, and does not include the crust or upper mantle. Understanding these distinctions is crucial for grasping the structure and dynamics of Earth's layers.