34.6 The Atmosphere

34.6.2 State the percentage of the two main gases in the atmosphere.

The two main gases in Earth's atmosphere are nitrogen and oxygen.

Nitrogen                    - 78%

Oxygen                      - 21%

34.6.4 Describe the variation of pressure as altitude increases.

As altitude increases, atmospheric pressure decreases.

This means that the air pressure becomes lower the higher you go in the atmosphere.

As you ascend in altitude, atmospheric pressure decreases at a rate of about 1 hPa roughly every 30 feet.

The decrease in pressure is due to the decreasing density of the air molecules as you move further away from the Earth's surface.