"Plate tectonics" refers to when the outer layer of a celestial body, such as a planet or moon, is made up of a crust of plates that move over time. The only known celestial bodies with plate tectonics are Earth and one of Jupiter's moons, Europa. Earth’s plates are made up of rocky plates that are thought to have shifted throughout history, causing earthquakes and resulting in separate continents, volcanoes and mountains. Europa is thought to have plate tectonics as well, but with a crust made of ice rather than rocks. Some scientists believe that this means that it could be suitable for human habitation.
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