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( Article Type: Explanation )

The atmosphere is the thin layer around the globe upon which all living things on earth depend for their survival. As a comparison, the thickness of the atmosphere around the Earth is the same as the thickness of the skin of an apple compared to its diameter.

The atmosphere consists of two main layers: the troposphere, which extends from sea level to about 17 kilometres up (about 95% of the mass of all the gases and 90% of water vapour are in this layer) and the stratosphere, which extends from 17 kilometres up to about 48 kilometres upwards. The ozone layer is in the upper part of the stratosphere. Above the stratosphere are two further layers called the ionosphere (which reflects radio waves between distant ground radio stations) and the exosphere (a zone of rarefied helium and hydrogen gases, which merges with ‘outer space’). A controlled environment is created by the atmosphere, which enables living beings of all kinds to survive.

The atmosphere acts as a shield against dangerous ultra- violet radiation and also forms an insulating layer, which raises the temperature to levels where life can comfortably exist. Without the insulating layer of the atmosphere, the temperature on earth would fall to –240º C at night.