2. Water and Weather

3. Chapter Five: Earth’s Atmosphere 5.1 The Atmosphere 5.2 Layers of the Atmosphere 5.3 Earth is Just Right

4. Investigation 5A Can you measure atmospheric pressure? The Atmosphere

5. 5.1 The Atmosphere Earth’s atmosphere is a layer of gases surrounding the planet. The atmosphere protects and supports life.

6. 5.1 What's in Earth's atmosphere? Earth’s atmosphere is made of a mixture of gases called air. Nitrogen gas makes up about 78% of Earth’s atmosphere. The second most abundant gas is oxygen, which makes up 21% of Earth’s atmosphere.

7. 5.1 Nitrogen Cycle Nitrogen is important to protein which is found in the body tissues of all living things. Nitrogen is cycled through the soil and into plants and finally when living things die and decay.

8. 5.1 The story of Earth’s atmosphere Earth’s unique atmosphere exists because our planet has the right balance between mass and distance from the Sun.

9. 5.1 Pressure in the atmosphere The gas molecules closest to Earth’s surface are packed together very closely. This means pressure is lower the higher up you go into the atmosphere.

10. 5.1 Pressure changes with altitude

11. 5.1 Pressure in the atmosphere At sea level, the weight of the column of air above a person is about 9,800 newtons (2,200 pounds)! This is equal to the weight of a small car. Why aren’t we crushed by this pressure?

12. 5.1 Measuring Pressure A barometer is an instrument that measures atmospheric pressure. Long ago, mercury barometers were used.

13. 5.1 Measuring Pressure Since mercury is a poisonous liquid, aneroid barometers are used today.