Which of the following is NOT part of the lithosphere?

• A. Asthenosphere
• B. Oceanic crust
• C. Continental crust
• D. Uppermost mantle

Answer: (A)

This question tests the distinction between the rigid outer shell and the underlying mantle. The lithosphere is the rigid outer layer that includes the crust (both continental and oceanic) and the uppermost part of the mantle. It behaves as a rigid shell that supports and interacts with the tectonic plates.

The oceanic crust and continental crust are clearly part of the lithosphere, as is the uppermost mantle, which together form the rigid shell that participates in plate tectonics. The asthenosphere, located beneath the lithosphere, is a weaker, more ductile layer that can flow slowly. Because of this plastic behavior, it is not considered part of the lithosphere.

So the correct idea is that the asthenosphere is not part of the lithosphere, while the crusts and the uppermost mantle are.