Which layer beneath the lithosphere is characterized as the hot, partially molten region that drives plate motion?

Which layer beneath the lithosphere is characterized as the hot, partially molten region that drives plate motion?

• A. Mantle
• B. Asthenosphere
• C. Core
• D. Crust

Answer: (B)

Plates move because they ride on a weak, partially molten layer below the rigid lithosphere. That layer is the asthenosphere. It sits in the upper mantle and is hot enough to deform easily, flowing slowly like a viscous plastic. This ductile behavior lets the overlying lithospheric plates slide relative to each other and be carried along by convection currents in the mantle, which is what drives plate motion. The other options don’t fit: the crust is the rigid outer shell, the core lies deep inside and isn’t involved in surface plate movement, and the mantle is a broad region—with the key partially molten, deformable portion that enables plate motion being the asthenosphere.

Plates move because they ride on a weak, partially molten layer below the rigid lithosphere. That layer is the asthenosphere. It sits in the upper mantle and is hot enough to deform easily, flowing slowly like a viscous plastic. This ductile behavior lets the overlying lithospheric plates slide relative to each other and be carried along by convection currents in the mantle, which is what drives plate motion. The other options don’t fit: the crust is the rigid outer shell, the core lies deep inside and isn’t involved in surface plate movement, and the mantle is a broad region—with the key partially molten, deformable portion that enables plate motion being the asthenosphere.