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illustration of mountain climber

Tenzig Norgay at the top of Mount Everest.

After weeks of climbing, Hillary and Norgay could only stay at the summit for 15 minutes, before they needed to begin their descent.

THE DEATH ZONE
One of the trickiest challenges of climbing Mount Everest is surviving the lack of oxygen at higher elevations. The summit, or top, of Everest sits 29,035 feet above sea level. At 20,000 feet up the mountain there is only half as much oxygen in the air as there is at sea level. At the very top there is only a third of the oxygen that people are used to at sea level. By the time climbers reach 26,000 feet, they enter “The Death Zone.” There is so little oxygen at that altitude that humans and animals cannot survive for more than a day or two.