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Transcript of Chapter 3
There is a layer of air around Earth. This air is made up of different gases. These gases are important to Earth's living things.
Carbon dioxide is a gas that helps hold heat close to Earth. It has no color or odor. People give off carbon dioxide when they breathe. Animals give off carbon dioxide when they breathe. Plants use carbon dioxide to make food. When plants make food, they give off oxygen.
1. List four gases that make up air.
On a cold night, it is good to have a blanket. Earth has a blanket, too. It is a layer of gases called the
. The Sun heats Earth. The atmosphere holds the heat close to Earth's surface.
3. Circle the point at which air pressure would be lowest. Draw a box around the point at which air pressure would be highest.
If you have ever been in a greenhouse, you know it is warm inside. The air in a greenhouse is usually warmer than the air outside. The glass walls and roof of a greenhouse let in light and heat from the Sun. The glass traps the heat. It lets little heat out. This keeps the plants inside warm.
The atmosphere has four layers. The lowest layer is called the troposphere. This layer begins at Earth's surface. Earth's weather occurs in this first layer.
is the conditions of the atmosphere at a certain place and time.
Chapter 3-Lesson 1
What Is Air?
Gases in Air
Did you ever wonder what is in the air you breathe? Air is made up of gases that have no color or smell. Air is all around Earth. The largest part of air is a gas called nitrogen. The next largest part of air is a gas called oxygen. Living things need oxygen to live. Your body needs oxygen to use the fuel in the food you eat. Most living things get oxygen they need from air.
Nitrogen and oxygen are not the only gases that make up air. Small amounts of other things are found in air too. Two of these things are carbon dioxide and water.
c. carbon dioxide
2. Label the arrows. Show how oxygen and carbon dioxide move between plants and animals.
Like all matter, air take up space. Air also has weight. The weight of air presses down on Earth all the time. This weight is called
High in the mountains there is less air pressing down on Earth. This means air pressure on a mountaintop is lower than it is at the bottom of the mountain.
Air is thin high in the mountains. Climbers carry oxygen with them to breathe.
Top of a mountain
Bottom of a mountain
Air pressure changes as you climb up a mountain. What do you think would happen if you climbed down into a deep canyon?
If I were to go down into a canyon, there would be more air above me than at the rim of the canyon, so air pressure would increase.
The next layer of the atmosphere is the stratosphere. Airplanes travel in this layer. This layer keeps a lot of the harmful part of the Sun's rays from reaching Earth.
The mesosphere is the next layer of the atmosphere. The coldest temperatures in the atmosphere are found here.
The top layer of the atmosphere is called the thermosphere. Space shuttles travel in this layer.
4. Read the clues. Then identify the layer of the atmosphere that is being described.
Layer of the Atmosphere
a. coldest layer
b. the layer in which weather occurs
c. the layer in which space shuttles orbit
d. the layer that keeps some harmful rays of the Sun from reaching earth
A greenhouse keeps plants warm on cold days.
The atmosphere keeps Earth warm in the same way. Earth's atmosphere lets in light and heat from the Sun. Some of the heat escapes into space. But the atmosphere holds most of the heat in.
This natural heating of Earth is called the greenhouse effect. The
is the process by which heat from the Sun builds up near Earth's surface. The atmosphere then traps the heat there. In recent years, carbon dioxide and other harmful gases have begun to build up in the atmosphere. Some scientists warn that this build up of gases will cause Earth's air to become warmer. This is called global warming.
5. The warming of air in a greenhouse is like the greenhouse effect in the atmosphere. Complete the chart to compare these processes.
In a greenhouse...
In the atmosphere...
let in heat and light.
traps the heat.
lets in heat and light.
in the atmosphere trap most of the heat.
Earth is surrounded by a layer of air that is made up of different gases. How are these gases important to living things?
Plants use nitrogen to grow.
Animals use oxygen to get energy from food.
c. Carbon dioxide:
Plants use carbon dioxide in air to make food.
Use the diagram to explain the greenhouse effect.
Heat from the Sun passes through the atmosphere. Some of the heat returns to space, but much of it is trapped by the gases in the atmosphere.
The diagram is on page 63 in your book.
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