Heterosphere

Part of speech: noun

Definitions

1. A segment of the atmosphere identified by distinct layers of gases organized according to their molecular weight
2. An area within the atmosphere where gases are arranged in layers, each layer consisting of gases of different densities
3. A part of the atmosphere where gases separate into layers based on their molecular masses

Etymology: The heterosphere is a compound built from two Greek-derived parts: "hetero-", from Greek "heteros" meaning "other" or "different", and "-sphere", from Greek "sphaira" meaning "ball" or "globe", which English came to use for a spherical region or domain. Put together, the term names a region of the upper atmosphere that is defined by its differences, in contrast to the more uniform layer beneath it. The distinction matters because of how gases behave with height. Lower down, turbulent mixing keeps the air well blended, so its composition stays fairly constant. Above that, the gases stop mixing and separate according to their weight, with the heaviest settling lowest and the lightest rising highest. The heterosphere is the zone where this separation takes hold, which is why its layers differ in density rather than forming one uniform mass.