Download What Is the Atmosphere?

Page 1 of 4
What Is the Atmosphere?
By Patti Hutchison
1
Earth, air, water, and fire. The ancient Greeks thought these
were the basic elements. They believed these could not be broken
down into parts. Today, we know more about the air around us. It
is made up of many gases. Together these gases make up the
atmosphere. This is a layer of air above the earth. It extends into
outer space.
2
What are the gases that make up the atmosphere? Ninety-nine
percent of air is nitrogen and oxygen. The other one percent is a mixture of water vapor,
argon, carbon dioxide, and other gases. Without the atmosphere, there would be no life
on our planet.
3
It is important that the amounts of nitrogen and oxygen in the atmosphere never
change. If either changed very much, life could not survive. But the amounts of the other
gases do change a little. These changes do not harm us.
4
The amount of water vapor in the air is always changing. It is always different over
different parts of the world. It may change over a certain place within a period of a day or
even a few hours. Water vapor may make up as much as four percent of the atmosphere.
What causes this variation?
5
The percentage of water vapor changes with the seasons. You know that warmer air
can hold more moisture than cooler air. So it makes sense that there is more water vapor
in the air in spring and summer. Likewise, cooler air in fall and winter is dryer. It doesn't
contain as much water vapor.
6
The amount of water vapor also varies over different surfaces. Air is dryer over the
desert than over the ocean. The air on the windward side of a mountain is moister than air
on the leeward side.
7
Our weather changes because of differences in the amounts of water vapor in the air.
Clouds, rain, and snow come from water vapor. Water is the only substance that comes in
three states. It can be frozen (solid), liquid, or gas. When it changes from one state to the
other, heat is soaked up or given off. This makes atmospheric motions that create
weather.
8
There are solid particles in the atmosphere. Dust and salt are left behind during
evaporation. These help clouds to form. This also affects our weather. Ice is another solid
found in the air. This usually comes in the form of hail or sleet.
9
The atmosphere is made up of several layers. The layer closest to the earth is called
the troposphere. This is where most of the water vapor is. Most weather takes place in
http://www.edhelperblog.com/cgi-bin/vspec.cgi?FORMMODE=RC37_146_1&QUI... 11/27/2013
Page 2 of 4
this layer. The air temperature decreases as you go from the bottom to the top of the
troposphere.
10
The next layer is called the stratosphere. Ozone is found here. This is a layer of
special oxygen molecules high above the earth. It absorbs harmful rays of the sun. If
there were no ozone, the sun would badly damage our skin. The stratosphere is warm
because it absorbs much of the radiation from the sun. The top of the stratosphere is
about 50 km above the earth's surface.
11
Above the stratosphere is the mesosphere. This layer is the coldest layer because
there is no ozone here. Beyond the mesosphere is the thermosphere. The temperature in
this layer is more than 1000 degrees Celsius. This layer is very thin. The molecules are
spread out. So it wouldn't feel that hot to you if you were to go through it.
12
Next comes the ionosphere. This is actually part of the thermosphere. It is made of
layers of very light gases. The last layer is the exosphere. Hydrogen and helium are found
here. Beyond this layer is outer space. But you won't "bump into" outer space. There is
no ceiling at the end of the atmosphere. The molecules are just spaced farther apart until
they don't exist anymore.
13
Animals need air to breathe. Plant life needs gases in the air for photosynthesis. Life
on earth could not exist without the atmosphere.
Copyright © 2013 edHelper
http://www.edhelperblog.com/cgi-bin/vspec.cgi?FORMMODE=RC37_146_1&QUI... 11/27/2013
Page 3 of 4
Name _____________________________
Date ___________________
What Is the Atmosphere?
1. Which two gases make up most of the
atmosphere?
Nitrogen and oxygen
Helium and hydrogen
Carbon dioxide and water vapor
3. Name three kinds of solid particles in
the air.
5. The layer of the atmosphere that is
closest to the earth is called:
The stratosphere
The exosphere
The troposphere
2. A change in the amount of water vapor
in the atmosphere will cause a change in
what?
Temperature
Nitrogen
Weather
4. A layer of special oxygen molecules
high above the earth is called:
Ozone
Clouds
Ionosphere
6. Why is the stratosphere warmer than the
upper troposphere?
http://www.edhelperblog.com/cgi-bin/vspec.cgi?FORMMODE=RC37_146_1&QUI... 11/27/2013