The Composition of the Atmosphere

The atmosphere is made up of many different gases. 78% of it is nitrogen, 20% of it is made up of oxygen, and the last 1% is mainly carbon dioxide, argon, and water vapor.

http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html

The Layers of the Atmosphere

There are four main levels of the atmosphere:thetroposphere, the stratosphere,the mesosphere, and the thermosphere. These layers are separated by changes in the temperature.At the end of each layer there is a pause like the tropopause or the mesopause.

http://www.uwsp.edu/geo/faculty/ritter/glossary/S_U/troposphere.html.

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