The atmosphere is made up of different gas molecules. As altitude decreases, air molecules are more densely packed together, creating higher air pressure. Airplanes without pressurized cabins can only fly in the lower troposphere where there is enough air pressure, while pressurized jet airplanes and satellites in orbit are able to operate in areas with less air pressure.

1. Atmosphere ES5 10.08

3. Troposphere Airplanes without pressurized cabins. Satellites orbiting in space (no atmosphere). Jet airplanes with pressurized cabins. The highest clouds

5. The atmosphere is a mixture of different molecules of gas.

6. The lower we go into the atmosphere the more densely the molecules of gas are pressed together.

7. Air molecules have weight. At lower elevations there is more air pressure.

14. (mostly CO2)