2. The Engine: Mantle Convection

Wegener's missing piece was a force big enough to move continents. The answer is heat — the same internal heat (from Earth's formation and from radioactive decay) that keeps the core molten.

That heat sets the mantle in motion. The mantle is solid rock, but it is so hot that over millions of years it flows very slowly, like incredibly stiff putty. Hot rock near the bottom rises, spreads out near the top, cools, and sinks again — a slow loop called a convection cell.

The rigid plates sit on top of these flowing currents and get carried along. Scientists now think two forces matter most:

• Ridge push — new, elevated crust at a mid-ocean ridge slides downhill, pushing the plate away.
• Slab pull — where a cold, dense plate edge sinks into the mantle, it pulls the rest of the plate along behind it. Slab pull is thought to be the strongest driver.

How fast? Only a few centimeters per year — about as fast as your fingernails grow. Tiny, but over millions of years it moves continents across the globe.

⚠️ Common misconception: the mantle is not boiling liquid lava. It is solid rock that flows in extreme slow motion. One convection loop can take tens of millions of years.

💡 Tip: heat → convection in the solid mantle → ridge push + slab pull → plates creep along at a few cm/year.