<P> High elevations on mountains produce colder climates than at sea level . These colder climates strongly affect the ecosystems of mountains: different elevations have different plants and animals . Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, such as mountain climbing . </P> <P> The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m (29,035 ft) above mean sea level . The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m (69,459 ft). </P> <P> There is no universally accepted definition of a mountain . Elevation, volume, relief, steepness, spacing and continuity have been used as criteria for defining a mountain . In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which, relatively to the adjacent elevation, is impressive or notable ." </P> <P> Whether a landform is called a mountain may depend on local usage . Mount Scott outside Lawton, Oklahoma is only 251 m (823 ft) from its base to its highest point . Whittow's Dictionary of Physical Geography states "Some authorities regard eminences above 600 metres (2,000 ft) as mountains, those below being referred to as hills ." </P>

How tall does a hill have to be a mountain
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