1. Atmosphere Layers of the atmosphere A. Layers of the Atmosphere
1. Troposphere Stratosphere
3. Mesosphere
4. Thermosphere*
* split into the Ionosphere and the Exosphere 1 2
Stratopause 3
Mesopause 4
Tropopause

2. Atmosphere B. Description of Atmosphere Layers 1. Troposphere
a. Tropo means “turning” or changing
b. extends from the earth’s surface from 12 kilometers in altitude
c. weather changes
d. COOLING TREND - temperature drops/cools as you go up
2. Stratosphere
a. extends from the Tropopause to an altitude of 50 kilometers (32 kilometers thick)
b. strong, steady winds
c. few weather changes
d. WARMING TREND - warms as you go up
e. contains the ozone layer – oxygen molecules that absorb ultraviolet radiation

3. Atmosphere 3. Mesosphere (Middle Layer) Thermosphere (Outermost layer)
a. rises from the Stratopause to 80 kilometers (30 kilometers thick)
b. COOLING TREND - temperature falls/drops as you go up
c. Protects Earth from meteors – they burn up here
d. Coldest part of the atmosphere
Thermosphere (Outermost layer)
rises from Mesopause to 300+ kilometers
WARMING TREND - temperature rises as you go up (hottest layer)
Splits into the Ionosphere ( km) and the exosphere (above 550 km)
d. Meteors Enter here

4. Atmosphere Gases in the Atmosphere (DRY AIR) 1. Nitrogen 78%
2. Oxygen 21%
3. Argon 0.9%
4. Carbon Dioxide 0.03%
5. All Others 0.01%

5. Atmosphere II. Air Quality
A. Sources of Pollutants – some occur naturally, but many are the results of human activity 
1. Natural Sources – forest fires, soil erosion, dust storms, wind carries mold and pollen, and volcanic eruptions
Human Activities – most pollutants occur from the burning of fossil fuels (cars and factories), farming, and construction
B. Smog and Acid Rain – caused by burning of fossil fuels
C. Improving Air Quality – state and federal governments have passed laws to reduce air pollution