What causes convection currents in the mantle?

• A. Movement caused by radioactive decay heat in the core.
• B. Rotation of the Earth.
• C. Cooling of the mantle from the surface.
• D. Tidal forces from the Moon.

Answer: (A)

Mantle convection happens because heat from inside the Earth makes parts of the mantle buoyant. When mantle material is heated by energy coming from the interior (including heat produced by radioactive decay in the core region), it becomes less dense and starts to rise. As it rises, cooler, denser mantle moves in to take its place and then cools, becomes denser, and sinks, forming a looping flow. This internal heat is the energy source that sustains the convection currents.

Rotation of the Earth can influence the path of the flow but doesn’t supply the driving force. Cooling from the surface can contribute to some near-surface movement, but the deep mantle convection is powered by internal heat—primarily from radiogenic processes in the interior—making the heat source in the core and mantle the key driver. Tidal forces from the Moon are far too weak to drive this process.