The structure of the atmosphere

The atmosphere is the air shell surrounding the Earth; “atmos” means vapour and “sphaira” ball. It rotates with the Earth, protects it from meteors and from the Sun’s harmful ultraviolet rays, and holds heat so that the difference between day and night is smaller; without an atmosphere the Earth, like the Moon, would heat to +120 °C by day and cool to about −170 °C at night. Air consists of 78 % nitrogen, 21 % oxygen and about 1 % other gases (carbon dioxide and others), plus water vapour and dust. The layers of the atmosphere: the troposphere (on average 10–11 km; 8–9 km over the poles and up to 17–18 km over the equator) holds water vapour, clouds, precipitation and weather, and temperature falls by an average of 6 °C for every 1000 m of height; the stratosphere (up to 50–55 km) contains the ozone layer; above it come the mesosphere, thermosphere and exosphere – the air is very thin and polar lights and “shooting stars” occur. The atmosphere has no sharp upper limit; space is taken to begin at about 100 km. Not polluting the air is everyone’s duty.