Which layer of the Earth includes the rigid outer layer consisting of the crust and uppermost mantle?

The lithosphere is the layer of the Earth that encompasses both the crust and the uppermost part of the mantle. It is characterized by its rigidity and solid state, which allows it to behave as a single, cohesive unit. The lithosphere is essential in tectonic processes because it is where tectonic plates are formed and move. These movements can lead to various geological activities, such as earthquakes and the formation of mountains.

In contrast, the asthenosphere, while located just beneath the lithosphere, is semi-fluid and allows for the movement of the rigid plates above. The mesosphere refers to the lower part of the mantle beneath the asthenosphere and is more rigid than the asthenosphere but does not include the crust. The core, which is primarily composed of iron and nickel, lies at the center of the Earth and does not include the crust or upper mantle. Thus, the lithosphere stands out as the correct choice, as it is the layer that integrates these two important elements of the Earth's structure.