Mount Everest is the highest mountain in the world. It is 8,850 metres above sea level. It was formed about 50 million years ago when the Eurasian and Indian continental plates collided. For local Tibetans and Sherpas, it was called Chomolungma, the Goddess Mother of the World. In 1856, it was declared the highest mountain. In 1865, it was renamed Everest after Sir George Everest. The first expeditions in the 1920s failed. Finally, on 29 May 1953, Edmund Hillary and Tenzing Norgay became the first to reach the summit. Since then, over 4,000 climbers have tried to reach the top, but more than 160 have died. Climbers face dangers such as avalanches, ice falls, and extreme weather.