Mountain
A mountain is a landform that extends above the surrounding terrain in a limited area. A mountain is generally steeper than a hill, but there is no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable summit. Mountains cover 54% of Asia, 36% of North America, 25% of Europe, 22% of South America, 17% of Australia, and 3% of Africa. As a whole, 24% of the Earth's land mass is mountainous. Also, 1 in 10 people live in mountainous regions. Most of the world's major rivers are fed from mountain sources,and more than half of humanity depends on mountains for water.[1][2]
The adjective montane is used to describe mountainous areas and the things associated with them.
Heights
Mountains are generally given as heights above mean sea level. The Himalayas average 5 km above sea level, whilst the Andes average 4 km. Most other mountain ranges average 2 – 2.5 km. The highest mountain on Earth is Everest, 8,848 m (29,029 feet), set in the world's most significant mountain range, the Himalayas.
Other definitions of height are possible. The peak that is farthest from the center of the Earth is Chimborazo in Ecuador. At 6,267 m above sea level it is not even the tallest peak in the Andes, but because Chimborazo is very close to the equator and the Earth bulges at the equator, it is 2,150 m further away from the Earth's center than Everest. The peak that rises farthest from its base is Mauna Kea on Hawaii, whose peak is over 9,000 m above its base on the floor of the Pacific Ocean.
Even though Everest is the highest mountain on Earth today, there have been much taller mountains in the past. During the Precambrian era, the Canadian Shield once had enormous mountains 12,000 m in height that are now eroded down into rolling hills. These enormous mountains formed by the collision of plate tectonics much like the Himalaya and the Rocky Mountains.
At 26 km (Fraknoi et al., 2004), the tallest known mountain in the solar system is Olympus Mons, located on Mars.
