Composition of Atmosphere : The atmosphere is mixture (composition) of many types of gases. It consists of 73% nitrogen, 21% oxygen and argon 0.9%. Other gases like carbon dioxide, hydrogen, helium and ozone are present in minute (small) quantities in the atmosphere. The lower layer of the atmosphere contains water vapor. This water is added to the lower layer of atmosphere from oceans, lakes and other water bodies by ways of evaporation. It is hardly 3-4% but it plays an important role in the atmosphere processes. Besides this, the lower layers of the atmosphere also contain dust, salt, pollen grains, etc.