The gaseous envelope surrounding the earth (or other heavenly bodies) its composition varies very slightly in different localities and according to altitude. The atmosphere is separated by gravity, centrifugal force and the influence of the sun on a number of concentric layers or spheres which are troposphere (lowest level), stratosphere, mesosphere, thermosphere (heterosphere), chemosphere (includes ozone layer) and the ionosphere. Air has no color, odor or definite shape, the volume% (composition) of clean air being – Nitrogen – 77.2%, Oxygen – 20.6%, Carbon dioxide – 0.04%, water vapors – varies from place to place, inert gases – 0.94% and other traces – approximately 0.003%.