An Etymological Dictionary of Astronomy and Astrophysics

Based on chemical composition, the atmosphere is divided into two broad layers: the → homosphere and the heterosphere. The heterosphere has heterogeneous chemical composition, with layered structure, of nitrogen, oxygen, helium, and hydrogen, respectively.
The heterosphere begins from about 90 km from the Earth’s surface and extends to space.

See also: → hetero-; → shere.