Which is the outermost solid layer of Earth, the top of the lithosphere?

• A. Echo Sounder
• B. Curie Point
• C. Core
• D. Crust

Answer: (D)

Think about Earth's layered structure and how the lithosphere sits on top of the planet. The outermost solid shell you would encounter is the crust, which forms the sea floor and the continents. The lithosphere includes both the crust and the rigid portion of the upper mantle, but its top edge at the surface is the crust itself. So, the topmost solid layer of Earth, the top of the lithosphere, is the crust.

The other options aren’t layers you’d find as a physical shell: an echo sounder is a depth-measuring instrument, the Curie Point relates to magnetic properties of rocks, and the core lies far deeper inside.