Mountains are an elevated portion of the Earth’s crust, generally with steep sides that show significantly exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least 300 metres above the surrounding land. A few mountains are isolated summits, but most occur in mountain ranges. The highest mountain on Planet Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m.