Which are the three main layers of the Earth, and what drives plate movement?

• A. Core, mantle, and crust; heat from core causes plate motion directly
• B. Crust, mantle, and core; lithosphere above ductile asthenosphere drives motion
• C. Lithosphere, asthenosphere, mesosphere; convection in outer core drives motion
• D. Crust, mantle, and core; mantle convection only in inner core

Answer: (B)

Understanding how Earth's structure relates to plate tectonics: the planet has three main layers—crust, mantle, and core. The plates are part of the rigid lithosphere, which sits atop the more ductile asthenosphere. Heat in the mantle drives convection currents there, and these currents slowly push and pull the lithosphere, causing plate movement. So the best description is crust, mantle, and core, with plate motion driven by the lithosphere moving on the ductile asthenosphere due to mantle convection. It isn’t accurate to say the motion comes directly from heat in the core, nor to credit convection in the outer core, and the mesosphere isn’t the relevant layer for driving plate tectonics.