1. The Atmosphere Chapter 17

2. Composition – What’s in the air? Earths atmosphere is a mixture of gases that has changed over time The atmosphere did not contain a significant amount of oxygen until 2.5 billion years ago The atmosphere continuously exchanges gases and particles with the oceans and with earths surface

3. Composition – What’s in the air? Major components of the atmosphere are about the same everywhere on earth Air is mostly nitrogen and oxygen (99%) The remaining 1% is argon 0.04% is carbon dioxide (CO 2 )

4. Composition – What’s in the air? Variable components change from place to place Dust - from smoke, ash, soil, and sea salt Ozone – protects life on Earth by absorbing harmful UV radiation Water vapor – the source of all clouds and precipitation. Absorbs heat from the earth and from the sun Pollution – particles and gases that are harmful to living things

6. Structure of the atmosphere Air is concentrated near Earths surface and thins as you travel away from Earth until the molecules are too spread out to detect. Air is a form of matter, so it exerts pressure on the Earth Air pressure decreases as you go higher in altitude

7. Structure of the Atmosphere The atmosphere is divided into 4 layers based on temperature Terms: Altitude - describes the height of something above the ground vs. Elevation – the height of a landform

8. Structure of the atmosphere Troposphere : 0 – 10 km above Earth All major weather events happen in the troposphere The troposphere has the most air particles The temperature of the air decreases as altitude increases The troposphere ends at the tropopause

9. Structure of the atmosphere Stratosphere: 10 – 50 km above Earth The ozone layer is located in the stratosphere Commercial airplanes travel in the stratosphere Temperatures increase as the altitude increases in the stratosphere This is because the ozone layer absorbs solar radiation The stratosphere ends at the stratopause

11. Structure of the atmosphere Mesosphere: 50 - 80 km above Earth Meteors entering Earth’s atmosphere usually burn up in the mesosphere Temperatures decrease as altitude increases in the mesosphere The mesosphere ends at the mesopause

13. Structure of the atmosphere Thermosphere: 80 – 140 km above Earth Aurora Borealis (The Northern Lights) occur in the thermosphere The thermosphere has the least amount of air particles Temperature increases as altitude increases in the thermosphere

16. What causes the northern lights?