Which layer has rocks that are plastic-like and flow?

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

Answer: (A)

Rocks that flow in a plastic-like way do so because they are hot and under pressure, which lets them deform gradually rather than crack. This ductile, slow flow characterizes the asthenosphere, the part of the upper mantle just beneath the rigid lithosphere. There, rocks are near their melting temperatures and can glide past one another, allowing the plates above to move. The other layers aren’t like this: the outer core is a liquid metal, not rock, and the inner core is a solid sphere; neither behaves like plastic rock. So the layer where rocks behave plastically and flow is the asthenosphere.