Which layer forms the rigid outer shell that combines the upper mantle and the crust?

• A. Mantle
• B. Lithosphere
• C. Crust
• D. Plate Tectonic Theory

Answer: (B)

The rigid outer shell that combines the crust with the upper part of the mantle is the lithosphere. This layer is characterized by its rigid, brittle behavior, and it includes both continental and oceanic crust along with the rigid portion of the upper mantle. The lithosphere sits atop the partially molten, more ductile asthenosphere, which allows the plates of the lithosphere to move very slowly.

This distinction matters because the mantle by itself isn’t the outer shell and doesn’t include the crust, while the crust alone is the outermost skin without the upper mantle portion. Plate Tectonic Theory is a concept about how these rigid plates move, not a layer of Earth.