In modern view regarding the structure of atmosphere, the atmosphere is divided into two broad spheres on the basis of composition.
I. Homospheres
Homosphere means zone of homogenous composition height-up to 88 km. The proportions of the component gases of the sphere are uniform at different levels. It is sub-divided into:
• Troposphere – Very shallow transition layer – Tropopause
• Stratosphere – Stratopause
• Mesosphere – Mesopause
II. Heterosphere
The atmosphere above the homosphere is not uniform in composition. Different layers of the atmosphere in this part differ from one another in their chemical and physical properties. In this sphere, gases are said to be arranged into the following four roughly spherical shells, each of which has its own distinctive composite.
(a) Nitrogen layer – 200 km above earth’s surface -molecular N.
(b) Oxygen layer – Average height 1120 km. – atomic oxygen
(c) Helium layer – 3520 km
(d) Hydrogen layer – Arranged based on the weight of the gases.
