Mountains are like hills, but bigger. A group of mountains close together is called a range of mountains. This map shows the main mountain ranges in the world:

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Mountains are made over millions of years, when parts of the Earth's surface crash into each other and are pushed upwards. In between the tall bits there are lower areas called valleys. These are usually made by rivers (V-shaped valleys) or glaciers (U-shaped valleys).

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Living in mountains can be very difficult because of the climate, but some wildlife manages to survive, and some people like to visit them for their holidays.