The Composition of Air in the Atmosphere
 The elements found in the atmosphere are found as molecules of gas.
 Air is a mixture of gaseous elements and compounds that changes throughout the atmosphere.
78%
Oxygen
21%
Argon
0.9%
Carbon
Dioxide
0.03% water vapor and other gases
0.07%
Air Pressure
 Air pressure decreases as altitude increases.
 When you climb a high mountain, you lose your breath easier because the air pressure decreases.
Temperature
 The layers of the atmosphere are classified according to changes in temperature.

The atmosphere is held in place by gravity.
The five layers of the atmosphere from space down to Earth are:
 Exosphere
- The outer most layer that merges with space.
- Satellites orbit in the exosphere.
- Has the lowest amount of air pressure.
- Contains the fewest particles (hydrogen and helium).
- The Ionosphere reaches into exosphere.
 Thermosphere
- Temperature increases (gets warmer) as altitude increases.
- This is the hottest and the thickest layer of the atmosphere.
- The thermosphere layer of the atmosphere includes part of the ionosphere.
- Radio waves bounce back to earth from the ionosphere.
- Northern and Southern Lights (auroras) occur in the ionosphere.
 Mesosphere
- Temperature decreases (gets colder) as altitude increases.
- Meteors burn up in this layer of the atmosphere.
 Stratosphere
- Temperature increases as altitude increases.
- The jet stream is located here. Jets can fly on this high speed air current that
moves from west to east across the U.S.
- The ozone layer is located here. The chemical formula for ozone is O
3
- The ozone layer provides protection from ultraviolet rays of the sun.
.
 Troposphere
- Temperature decreases as altitude increases in the troposphere.
- Most (75%) of the air that makes up the atmosphere is found in the troposphere.
- Most airplanes fly in the troposphere.
- Most of the Earth's weather occurs in the troposphere.
- The majority of the water vapor in the Earth’s atmosphere is found in the troposphere.
- The troposphere has the greatest amount of air pressure.
Remember to always review all of the notes and handouts in your science binder!