Which layer beneath the lithosphere is the hot, plastic region that powers plate tectonics?

• A. Continental Crust
• B. Asthenosphere
• C. Basalt
• D. Body Wave

Answer: (B)

The idea being tested is that plate tectonics is driven by a hot, ductile zone in the upper mantle. This region, called the asthenosphere, behaves plastically due to high temperatures and pressures, so rocks there can flow slowly instead of cracking. That soft, viscous layer lets the rigid lithospheric plates move and even ride on convection currents within the mantle. Continental crust isn’t a separate layer beneath the lithosphere, it’s part of the lithosphere itself. Basalt is a rock type common in the oceanic crust, not a mantle layer. Body waves are seismic waves used to study Earth, not a mantle layer. So, the asthenosphere is the hot, plastic region beneath the lithosphere that powers plate tectonics.