About 200 million years ago, a supercontinent split apart, and the Atlantic Ocean was born. Last year, the Atlantic widened by about this much: . In another 200 million years, it may be twice as wide as it is today. Slowly but relentlessly, powered by Earth's internal heat engine, plate tectonics rearranges land and sea. Our planet's surface has been changing for 4.6 billion years...and it's still happening today.

• Plate Tectonics 101