How do the lithosphere and asthenosphere differ?

How do the lithosphere and asthenosphere differ?

• A. The lithosphere is totally rigid, whereas the asthenosphere is not.
• B. The lithosphere is partially molten, whereas the asthenosphere is completely rigid.
• C. The lithosphere lies beneath the asthenosphere.
• D. The lithosphere and asthenosphere have identical properties.

Answer: (A)

The main idea is how these two layers respond to stress: rigidity versus the ability to flow. The lithosphere acts as a rigid, strong shell—made up of the crust and the uppermost mantle—that tends to resist deformation and break rather than flow. The asthenosphere lies beneath it and is hotter and weaker, so rocks there behave in a ductile, slowly flowing way rather than as a rigid solid. This contrast lets tectonic plates (the lithosphere) move around atop the softer, more deformable asthenosphere.

So describing the lithosphere as totally rigid and the asthenosphere as not rigid captures that essential difference, even though in reality the lithosphere isn’t perfectly rigid and the asthenosphere isn’t completely molten. The other statements don’t fit because they misstate the relationship or the properties: the lithosphere isn’t partially molten, the asthenosphere isn’t completely rigid, the lithosphere sits above—not beneath—the asthenosphere, and they do not share identical properties.