Structure and gas composition of the atmosphere

The atmosphere is not just the air breathed by people, animals and plants. It is also a gaseous substance enveloping the earth, protecting it from abrupt changes in temperature (without the atmosphere, daily variations in the temperature on the planet would reach 200 C) and protecting all living things from harmful solar and cosmic radiation. The direct and indirect influences of the atmosphere on man are varied.

The atmosphere consists of the following basic strata:

1. The troposphere reaches to a height of 8 to 17 kilometres; it contains 80 per cent of the atmospheric mass and water vapour; the weather phenomena develop in it.
2. The stratosphere is the layer above the troposphere and reaches to an altitude of about 40 kilometres. The greatest concentration of ozone (O) is observed in the stratosphere’s upper level.. The ozone absorbs most of the ultraviolet radiation and protects life from its harmful effect.
3. The ionosphere is the layer above the stratosphere containing highly ionised gas molecules. This layer protects the biosphere from the harmful effect of cosmic radiation and influences the reflection and absorption of radio waves; the northern lights originate here.
4. The exosphere is located above the ionosphere and is also known as the dispersal sphere, because the gas molecules of this layer are disposed into outer space.

It is impossible to exactly determine the upper limit of the earth’s atmosphere. The higher the altitude the less dense the air. At sufficiently high altitudes, the air density is higher than that of the interplanetary space. Up to 250 kilometres, the atmosphere is composed of the following gases: nitrogen 78.09 per cent (by volume), oxygen 20.95 per cent, argon 0.93 per cent, carbon dioxide 0.03 per cent, as well as small quantities of neon, helium, krypton, xenon, hydrogen and ozone. According to Soviet space research, the principal component of the atmosphere at a height of 250 to 300 kilometres is atomic oxygen. Even higher, beginning at a height of 500 to 600 kilometres, the atmosphere becomes a mixture of helium and hydrogen, and its very outer layer consists of atomic hydrogen.

Besides gases, the atmosphere always contains a certain amount of water vapours and various admixtures.