1. The Atmosphere
Chapter 6

2. About the Photo Imagine climbing a mountain and taking only one out of three breaths! As altitude increases, the density of the atmosphere decreases. At the heights shown in this picture, the atmosphere is so thin that it contains only 30% of the amount of oxygen found in the atmosphere at sea level. So, most mountaineers carry part of their atmosphere with them—in the form of oxygen tanks.

3. Characteristics of the Atmosphere
The atmosphere is a mixture of gases that surrounds Earth. In addition to containing the oxygen you need to breathe, the atmosphere protects you from the sun's damaging rays. The atmosphere is always changing. Every breath you take, every tree that is planted, and every vehicle you ride in affects the atmosphere's composition.

4. Composition of the Atmosphere

5. Water is also found in the atmosphere.
Liquid water (water droplets) and solid water (snow and ice crystals) are found in clouds. But most water in the atmosphere exists as an invisible gas called water vapor. When atmospheric conditions change, water vapor can change into solid or liquid water, and rain or snow might fall from the sky.

6.  Describe the three physical states of water in the atmosphere.1. 2. 3.

7. Atmospheric Pressure and Temperature
What would carrying a column of air that is 700 km high feel like? You may be surprised to learn that you carry this load every day. While air is not very heavy, its weight adds up. At sea level, a square inch of surface area is under almost 15 lb of air. Carrying that much air on such a small surface area is like carrying a large bowling ball on the tip of your finger!

8.                                                                                                                                                    
As in a human pyramid, air pressure increases closer to the Earth's surface. 

9. Atmospheric Pressure and Temperature
The atmosphere is held around the Earth by gravity. Gravity pulls gas molecules in the atmosphere toward the Earth’s surface, causing air pressure.
As altitude increases (distance from the earth’s surface), air pressure decreases.
Air temperature decreases as altitude increases too. Lower parts of the atmosphere are warmer because they contain a high percentage of gases that absorb solar energy.

10. Atmospheric Composition Affects Air Temperature
Air temperature also changes as altitude increases. The temperature differences result mainly from the way solar energy is absorbed as it moves through the atmosphere. Some parts of the atmosphere are warmer because they contain a high percentage of gases that absorb solar energy. Other parts of the atmosphere contain less of these gases and are cooler.

11. Layers of the Atmosphere
                                                                                                                                                   
The layers of the atmosphere are defined by changes in temperature.

12. Which layer of the atmosphere is closest to Earth?

13. Troposphere

14. -sphere means "ball," which suggests that each layer of the atmosphere surrounds the Earth like a hollow ball.
Tropo- means "turning" or "change," and the troposphere is the layer where gases turn and mix.
Strato- means "layer," and the stratosphere is the sphere where gases are layered and do not mix very much.
Meso- means "middle," and the mesosphere is the middle layer. Finally,
thermo- means "heat," and the thermosphere is the sphere where temperatures are highest.

15. What does the name of each atmospheric layer mean?
-sphere
Tropo-
Strato-
Meso-
thermo-

16. The Troposphere: The Layer in Which We Live
The lowest layer of the atmosphere, which lies next to the Earth's surface, is called the troposphere.
the densest atmospheric layer and contains almost 90% of the atmosphere's total mass.
Has almost all of the Earth's gases, weather, and life-forms.
Temperatures vary greatly here
Differences in air temperature and density cause gases in the troposphere to mix continuously.

17. As altitude increases in the troposphere, temperature decreases
As altitude increases in the troposphere, temperature decreases. Snow remains all year on this mountain.
                                                                           
Figure 4 As altitude increases in the troposphere, temperature decreases. Snow remains all year on this

18. The Stratosphere: Home of the Ozone Layer
The atmospheric layer above the tropo sphere is called the stratosphere.
Gases in the stratosphere are layered and do not mix as much as gases in the troposphere.
The air is also very thin in the stratosphere and contains little moisture.
The lower stratosphere is extremely cold.
Unlike the troposphere temperature rises as altitude increases in the stratosphere. This rise happens because ozone in the stratosphere absorbs ultraviolet radiation from the sun, which warms the air.
Almost all of the ozone in the stratosphere is contained in the ozone layer.
The ozone layer protects life on Earth by absorbing harmful ultraviolet radiation.

19. How does temperature change within the stratosphere?

20. For the first few kilometers, the temperature remains fairly constant
For the first few kilometers, the temperature remains fairly constant. Then, the temperature begins rising steeply and levels off again toward the top of the layer.

21. This photograph of Earth's atmosphere was taken from space
This photograph of Earth's atmosphere was taken from space. The troposphere is the yellow layer; the stratosphere is the white layer.

22. The Mesosphere: The Middle Layer
Above the stratosphere is the mesosphere. The mesosphere is the middle layer of the atmosphere.
It is also the coldest layer.
Like the troposphere, the temperature decreases as altitude increases in the mesosphere.

23. The Thermosphere: The Edge of the Atmosphere
The uppermost atmospheric layer is called the thermosphere. In the thermosphere, temperature again increases with altitude. Atoms of nitrogen and oxygen absorb high-energy solar radiation and release thermal energy, which causes temperatures in the thermosphere to be 1,000°C or higher. Although the thermosphere has very high temperatures, it does not feel hot. Temperature is different from heat. Temperature is a measure of the average energy of particles in motion. The high temperature of the thermosphere means that particles in that layer are moving very fast. Heat, however, is the transfer of thermal energy between objects of different temperatures. Particles must touch one another to transfer thermal energy. The space between particles in the thermosphere is so great that particles do not transfer much energy. In other words, the density of the thermosphere is so low that particles do not often collide and transfer energy.

24. Temperature in the Troposphere and the Thermosphere

25. Which atmospheric layer has the greatest temperature range?

26. Thermosphere.
Why doesn’t it feel hot?

27. The Ionosphere: Home of the Auroras
Charged particles in the ionosphere cause auroras, or northern and southern lights. 

28. Explain how density affects the transfer of thermal energy.

29. The less dense the air is, the less effective it is at transferring thermal energy. Particles must collide with one another to transfer energy. Particles farther apart are less likely to collide with other particles than particles that are close together.

30. Section Summary
Nitrogen and oxygen make up most of Earth's atmosphere. •
Air pressure decreases as altitude increases. •
The composition of atmospheric layers affects their temperature. •
The troposphere is the lowest atmospheric layer. It is the layer in which we live. •
The stratosphere contains the ozone layer, which protects us from harmful UV radiation. •
The mesosphere is the coldest atmospheric layer. •
The thermosphere is the uppermost layer of the atmosphere.

31. Section Quiz
Write the letter of the correct answer in the space provided.
_____ 1. Which answer best describes Earth’s atmosphere?
a. mostly oxygen with about 21% nitrogen
b. mostly nitrogen with about 21% oxygen
c. mostly carbon dioxide with about 21% oxygen
d. mostly nitrogen with about 21% carbon dioxide
_____ 2. What causes differences in air temperatures at different altitudes?
a. mainly the way air radiates solar energy
b. mainly the way gases radiate light
c. mainly the way gases absorb solar energy
d. mainly the way moisture moves through the atmosphere
_____ 3. What are the two highest layers of the atmosphere?
a. troposphere, mesosphere
b. thermosphere, mesosphere
c. stratosphere, thermosphere
d. troposphere, stratosphere
_____ 4. Auroras are caused by electrically charged particles in the
a. mesosphere.
b. troposphere.
c. hemisphere.
d. ionosphere.

32. Match the correct definition with the correct term
Match the correct definition with the correct term. Write the letter in the space
provided.
_____ 5. layered gases, thin air, little moisture
_____ 6. coldest layer, temperature decreases as
altitude increases
_____ 7. lack of particle density, little thermal
energy transfer
_____ 8. densest layer, contains almost 90% of
the atmosphere’s mass
a. troposphere
b. thermosphere
c. stratosphere
d. mesosphere