Final answer:
The lithosphere is defined as the crust and the upper mantle. It is the outermost mechanical layer of the Earth that behaves as a brittle, rigid solid.
Step-by-step explanation:
The lithosphere is defined as the crust and the upper mantle. It is the outermost mechanical layer of the Earth that behaves as a brittle, rigid solid. The lithosphere is about 100 kilometers thick and includes both the crust and the portion of the upper mantle that exhibits brittle behavior.