Where do convection currents that move tectonic plates originate?

• A. In Earth's core
• B. In the mantle
• C. In the atmosphere
• D. In the oceans

Answer: (B)

Mantle convection is the motion that drives plate tectonics. Heat from deep inside Earth causes mantle rock to circulate: hot material near the bottom becomes buoyant and rises, then cools as it moves upward and sinks again. This slow churning creates a conveyor-like flow that the rigid lithospheric plates ride on, causing them to move, collide, and spread at the surface. The heat source includes core heat and long-lived radioactive decay, but the convection that moves the plates happens in the mantle itself. The atmosphere and oceans have their own convection from solar heating, but they do not move tectonic plates.