<p>Earth’s Crust Moves</p><p>Earth’s surface is not a single piece of rock. Instead, it is made up of many plates. Plates are rigid blocks of crust and upper mantle rock. Most of North America, Greenland, and the western half of the North Atlantic Ocean are on the North American Plate. Part of California and most of the Pacific Ocean make up the Pacific Plate. There are about 20 plates in all. Earth’s plates fit together like the pieces of a jigsaw puzzle. Although these plates are enormous, they actually float on the soft, mushy rock of the mantle. Pressure and heat within the Earth produce currents in the soft rock of the mantle. As the mantle moves, the plates floating on it move, too. Some of the plates move up to two inches a year. That’s about as fast as a fingernail grows. But because plates are right next to each other, the movement of one plate affects other plates. Some plates push together. Some pull apart. Other plates slide past each other. As plates move around, they cause great changes in Earth’s landforms. Where plates collide, energy is released, and new landforms are produced. On land, mountains rise and volcanoes erupt. South America’s Andes Mountains are a result of the Nazca and South American plates colliding. On the ocean floor, deep trenches form. As plates pull apart on land, valleys dotted with volcanoes develop. Africa’s Great Rift Valley was formed by the African and Arabian plates pulling apart. The rift, or crack, will one day result in a complete separation of part of eastern Africa from the rest of the continent. Where plates pull apart under the sea, ridges and volcanoes form. This spreading forms new sea floor at the ridges. When plates scrape and slide past each other, they shake Earth’s surface. Along the San Andreas fault in California, the Pacific plate is moving past the North American plate. The plates rub and shake as they grind past each other causing earthquakes.</p><p>√What are Earth’s plates?</p>