Final answer:
The crust is part of the lithosphere, which also includes the uppermost mantle, both characterized by brittleness and rigidity. The correct answer is that the lithosphere is composed of the crust and part of the upper mantle, while the asthenosphere is a separate, plastically behaving layer beneath it.
Step-by-step explanation:
The relationship between the crust and the lithosphere is commonly misunderstood. The crust is Earth's outer surface, while the lithosphere consists of the crust plus the uppermost brittle portion of the mantle. In contrast, the asthenosphere is the partially molten upper mantle that behaves more plastically. Therefore, the answer is that the lithosphere includes the crust.
Compositional and Mechanical Layers of the Earth
Within Earth's interior, there are layers like the core, mantle, and crust that are defined by their chemical composition. However, when referring to mechanical properties, we divide the Earth into the lithosphere and the asthenosphere. As such, the lithosphere incorporates the compositional element of the crust and adds to it the mechanically similar upper mantle.
Understanding these distinctions is crucial for comprehending plate tectonics, where tectonic plates consist of crust and the rigid upper mantle—collectively referred to as the lithosphere. These plates float atop the more ductile asthenosphere, driving geological processes like earthquakes and volcanic activity.