The Atmosphere

The atmosphere is defined as the layer of gases that surrounds the earth.

Air is the mixture of gases that make up the atmosphere.

Air is approximately:

• 78% nitrogen
• 21% oxygen
• 1% carbon dioxide, water vapor, methane, other gases

The earth's atmosphere is often said to be about 100 miles thick, but it really has no upper boundary. It just gets thinner and thinner until there are hardly any molecules of air left.

The earth's atmosphere is divided into 4 layers. Since air is invisible, there is no visible boundary between the layers. But the composition of the gases and temperature trends are different in the different layers.

The following are the 4 layers from bottom to top:

1. Troposphere - the layer we live in
2. Stratosphere - contains the ozone layer
   • The ozone layer absorbs and protects us from ultraviolet light. The formula for ozone is O₃.
3. Mesosphere - "Shooting Stars" or meteors usually burn up in this layer.
4. Thermosphere - outer layer, contains the ionosphere, tapers off to nothing in outer space
   • The Ionosphere is a layer of charged ions that reflects short-wave radio waves.