Earth’s atmosphere

You’re standing at the edge of a small airfield, looking up at the blue sky. Suddenly, you spot a colourful dot above you, then another and another. Something is falling from the sky and getting bigger and bigger. Soon the colourful dots turn into paragliders, with people hanging beneath them. A short while later, they land safely and fold up their gliders. The canopies are very light and made from a special fabric. After a jump from an aircraft, they open up to form a bowl that is open at the bottom and fills with air. The trapped air slows the skydiver’s fall. Without air, the parachute would not open, and the skydiver would hit the ground at high speed and die. But of course, no one would jump then. In fact, there would be no one able to jump, because without air there would be no people at all.

We need this air to live—or, more precisely, we need the oxygen it contains. Air is all around us. It is made up of tiny particles called molecules. There are especially many of them close to the ground. High up on a mountain, there are far fewer air particles, and therefore less oxygen. That is why breathing is harder at high altitudes, and moving around takes much more effort than at lower elevations. When mountaineers climb the highest mountains on Earth, most can only make it if they bring oxygen and breathe it in as well. The layer of air surrounding our planet is very thin. One way to picture this is to imagine shrinking Earth to the size of a child—about 1.30 meters tall. The layer of air would then be just over 1 centimeter thick.

Only in the lowest layer, which would be about half a millimetre thick, would people get enough oxygen. In the layers above, the air is so thin that we would suffocate. There is much less air and hardly any oxygen. We call the Earth's envelope of air the atmosphere. It is divided into several layers. The lowest layer is called the troposphere. It extends up to an altitude of 15 km and contains 90 per cent of all the air particles surrounding the Earth. Weather occurs in the troposphere because the air can mix. Warm air rises, while cold air flows down. There are clouds, precipitation, winds and storms. Aircraft can fly only here, because only here is there enough air to support them. The higher a plane flies, the colder it gets outside. The plane in the next picture is flying at almost 12 kilometres. At this altitude, it is -50° Celsius, and there are hardly any clouds.

It is warmest right at ground level. Heat in the lower layers of the troposphere also helps keep the Earth from cooling down at night. Above the troposphere lies the stratosphere . This layer contains a particularly large amount of ozone. This gas filters UV radiation from sunlight. Without the ozone layer, we would not be able to withstand the sun’s rays. Our skin would constantly suffer severe sunburn. 

The stratosphere reaches an altitude of about 50 kilometres. Above it lies the mesosphere, beyond which outer space begins. Above that is the thermosphere, which contains very few air particles. In this layer, the temperature rises sharply. It extends to an altitude of about 500 kilometres. Beyond it lies the exosphere, which contains almost no air particles.