What is the lithosphere in plate tectonics?

• A. The rigid outer shell of the Earth that includes the crust and the uppermost mantle, which forms tectonic plates.
• B. The liquid layer of the outer core.
• C. The entire mantle.
• D. The atmosphere above the crust.

Answer: (A)

The lithosphere is the rigid outer shell of the Earth, made up of the crust and the uppermost part of the mantle, and it forms the tectonic plates. This rigid shell sits on the softer, partially molten layer beneath (the asthenosphere), which allows the plates to move slowly over time. The other descriptions point to different parts of Earth: the liquid layer of the outer core is far below and not part of the rigid shell; the entire mantle includes both rigid and more ductile regions and isn’t the distinct brittle shell that makes up plates; and the atmosphere above the crust is a gaseous layer, not rock. So, describing the lithosphere as the rigid outer shell that includes the crust and upper mantle and forms the tectonic plates best captures what the term means.