The atmosphere and its layers

In short: The atmosphere is the Earth’s envelope of air. It supplies oxygen to breathe, holds in warmth, protects against harmful radiation and is where weather happens.

In more detail: Dry air is about 78 per cent nitrogen, about 21 per cent oxygen and just under one per cent argon; carbon dioxide makes up only about 0.04 per cent. Based on how temperature changes with height, the atmosphere is divided into several layers.

In detail

• Troposphere: The lowest layer reaches about 8 kilometres high at the poles and about 17 kilometres at the equator. Almost all clouds and weather occur here, and temperature falls with height.
• Stratosphere: Above it, up to about 50 kilometres, lies the stratosphere. It contains the ozone layer, which absorbs UV radiation and warms the air as it does so. Airliners often fly near its lower boundary.
• Mesosphere: Up to about 85 kilometres it gets colder again. This is where the lowest temperatures in the atmosphere are found, and most shooting stars burn up at this height.
• Thermosphere: The very thin air above is strongly heated by solar radiation. Auroras glow in this layer, and the International Space Station orbits here at about 400 kilometres.
• Exosphere: At the outer edge the atmosphere gradually merges into space. Individual particles can escape into space from here.
• Edge of space: There is no fixed boundary. The Kármán line at 100 kilometres is often taken as the start of space.
• Falling pressure: Air pressure roughly halves every five to six kilometres. On high mountains there is therefore less oxygen in each breath.
• Warm blanket: Water vapour, carbon dioxide and other gases hold back heat. Without this natural greenhouse effect the Earth would be hostilely cold.
• Further reading: The ozone layer, spaceflight and weather are closely linked to the atmosphere (ozonschicht-und-ozonloch, satelliten-und-iss, luftdruck-und-wetter).