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World map showing the tectonic plates that make up the Earth’s crust. The place where the Eurasian and African plates meet the North and South American plates is known as the Mid-Atlantic Ridge. Earthquakes and volcanic activity are common in the places where tectonic plates meet.

water and solidifies to form submarine mountain chains called mid-ocean ridges . The longest of these, the Mid-Atlantic Ridge, is 43,500 miles (70,000 km) long, running from Spitzbergen in the Arctic almost to Antarctica. The two sides of the ridge are steadily moving apart, and this is pushing the Americas away from Europe and Africa. The same thing is happening to the Red Sea between North Africa and the Middle East, which is getting one inch wider every year. In a hundred million years’ time, the Red Sea could be an ocean as big as the Atlantic.

What Are Oceans? 13