Which layer lies directly beneath the lithosphere and allows for plate motion due to its ductile properties?

• A. Asthenosphere
• B. Mantle
• C. Outer Core
• D. Inner Core

Answer: (A)

The mechanism of plate motion rests on a soft, deformable layer beneath the lithosphere. This layer is the asthenosphere, part of the upper mantle. Its rocks are hot and under pressure just enough to behave plastically, so they can flow slowly rather than break rigidly. That ductile, weak behavior lets the rigid lithospheric plates ride and move on top of it, and convection within this layer helps drive their movement. The deeper layers—the outer and inner cores—are far below and do not provide the sliding surface for plates, and while the mantle includes the asthenosphere, the specific layer enabling motion directly under the lithosphere is the asthenosphere.