Why does air at the top of Everest contain only half the oxygen of air at sea level?

Air is retained on the surface of the Earth due to gravity. At sea level the air is dense and compressed to a breathable level by all the layers of the atmosphere above it. As you go further up there is less pressure pushing down the air, therefore less oxygen is available. Climbers on Everest acclimatise to the lack of oxygen by spending days and even weeks at around 7,925 metres (26,000 feet) in an area called the Death Zone. Once their bodies are used to the low levels of oxygen content in the air they can climb the final 914 metres (3,000 feet) or so to the summit.

Find the answer to more curious questions in How It Works magazine. Order it in printdownload it onto your digital device or subscribe today to ensure you never miss an issue!

Plus, take a look at:

Why does air pressure alter at different altitudes?

When does a hill become a mountain?

Why is it colder at the top of a mountain?