The Earth's Atmosphere

The Atmosphere: "The atmosphere describes all the air surrounding the earth, from the ground all the way up to the edge of deep space. The atmosphere is composed of several layers, each defined because of the various phenomena which occur within the layer. These transitions are gradual, and most heights and measurements mentioned below refer to the average area of transition from one layer to another."

Just because I needed to look it up to answer a question I had.

Link:
http://www.pbs.org/.../science/atmosphere.html#thermosphere