The atmosphere is the gaseous mass surrounding the earth. The earth’s atmosphere is made up of nitrogen (about 78%), oxygen (about 21%), argon (less than 1%) and carbon dioxide (less than 0.05%) along with small amounts of other gases and varying amounts of water vapour. The troposphere is the lowest layer of the earth’s atmosphere, its thickness varying from about 7 km to a maximum of around 16 km at the equator. Air temperature in the troposphere decreases as height increases. It is in this layer that most meteorological phenomena occur. The next layer is the stratosphere reaching up to about 50 km. Temperatures in this layer remain fairly constant as radiation from the sun neutralizes the effect of density decrease. Above the stratosphere is the mesosphere, which extends to around 80 km and in which temperature decreases with height. This is followed by the thermosphere, characterized by an increase in temperature with height and lying within the ionosphere (a region of the uppermost atmosphere that reflects short radio waves). The outermost layer, from about 400 km, is the exosphere. The atmosphere protects the earth from excessive radiation and is a vital factor in maintaining our planet’s heat balance.

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