By Arnie Cerny
- Students will describe and compare the layers of the atmosphere.
- Students will explain how to measure the temperature of the atmosphere.
- Students will explain what causes the atmosphere to heat up in some places more than in others.
1/4 glass of limewater or bromothymol blue, straws, overhead projector, styrofoam balls, large posterboard, flashlight, sheet of black paper
The earth is surrounded by a blanket of air that extends to about 1,000 km above its surface. The molecules of gas are trapped by the pull of the earth's gravity. The composition of the gas mixture in our atmosphere has evolved through time to its present values: nitrogen - 79%; oxygen - 20%; water vapor, carbon dioxide, and argon gases constituting the other 1%. Organisms need oxygen to release the energy from their food. This process is called respiration. Plants need carbon dioxide to make food during the process of photosynthesis. Nitrogen is used to make living matter. However, animals and plants cannot use it directly from the atmosphere. Plants absorb nitrates from the soil. Animals obtain nitrogen from the plants they eat becoming part of the animal's body.
Most of the gases were ejected from the earth's crust during long periods of volcanic activity. The atmosphere is separated into distinct layers based on the temperature changes that occur from one layer to the next. The layer of the atmosphere closest to the Earth is the troposphere. This is where we lice and where most weather occurs. As you go higher into the troposphere, the temperature drops. The sun's rays heat the surface of the earth, not the air directly. Therefore, air closest to the ground is the warmest. The thickness of this layer varies from 17.6 km at the equator to 6.4 km at the poles. The stratosphere lies above the troposphere. Air in the stratosphere is thinner than in the troposphere. It contains very little moisture and dust. As a result, practically no weather phenomena exist. Ozone is found in this layer about 15 - 50 km high. It is a form of gas that absorbs most of the harmful ultraviolet rays from the sun. A significant reduction in ozone would cause an unhealthy increase in radiation. The stratosphere contains broad, fast-flowing "rivers" of air circulating around the world. These are called jet streams. The jet streams can change weather patterns in the troposphere. Above the ozone layer of the stratosphere, temperature begins to drop once more. This is the beginning of the mesosphere. Temperatures reach -75 C. to about 80 km above the earth. Then temperatures begin to rise again in the top layer of the atmosphere, called the thermosphere. The gases continue to thin out to an altitude of about 600 km. The temperature may reach 2000 C. due to solar radiation absorption of gases. When solar energy is absorbed directly by air molecules, the atoms gain or lose electrons and become charged particles called ions. Many gas molecules between the altitudes of 80 - 400 km in the mesosphere and the thermosphere have electrically charged particles. This part of the atmosphere is called the ionosphere. The ionosphere is important in communications. It can reflect many types of radio waves allowing them to bounce around the world. To illustrate the atmosphere, picture yourself on top of an ocean of water that is about four hundred miles deep. Assuming one could survive the depths of this ocean, you rapidly descend to the bottom in a submarine. If the sub could dive at the rate of 88 km/hr (55 mph), your journey would take more than seven hours. On the bottom of the ocean you leave your sub to observe the changing ocean above, noticing that it is cooler down here than it was at the top.
Imagine the ocean above as our atmosphere, and you are now on the bottom of the ocean of air. As you gaze upward you are looking through about 500 km (310 miles) of air. In general, the density and temperature of the air decrease with elevation. Phenomena associated with the weather occur in the troposphere. The gases in the air are part of natural earth cycles.
Several factors affect the amount of radiation that is absorbed by the earth at different places. Because the earth is a sphere, the sun's rays strike different places at different angles. Near the equator the sun passes almost directly overhead. North and south of the equator, the surface of the sphere curves away from the sun. As a result, these locations receive less solar energy. Other factors include the tilt of the earth's axis, its day and night periods, and its path around the sun. Unequal absorption of radiation causes unequal heating of the earth's surface. Because the atmosphere is heated by the earth's surface, it too is heated unequally. Air near the equator is heated more than air near the poles. Heated air expands. Thus warm air at the equator is less dense than cold air at the poles. The density of the air determines the force with which it presses down on the earth's surface. This force is measured as air pressure. Cold air presses down on the earth with a greater pressure than warm air. Cold air is said to have a high pressure. Warm air is said to have a low pressure.
- Describe what happens to the temperature at different times of the day. Why are there changes?
- What causes the air temperature to become warm?
- How do surfaces affect air temperatures?
Describe and compare the layers of the atmosphere. Begin lesson by asking questions to find out what students already know about weather. Example: How did you decide what to wear to school today? Some students may indicate that the temperature had an influence on what they wore. Pursue the idea that weather often determines what we wear and what we do. Ask why we wear different clothing in the winter. Students may respond that the weather changes. Ask them for their own definition of weather. Try to relate that weather is the condition of the air around up and that temperature is one of the factors that effect air causing changes in weather. Continue to point out that the atmosphere is the air, like a blanket, around us.
Explore the composition of air. Draw a pie graph on chalkboard showing the four major gases in the air: nitrogen - 79% - essential to all plants and animal tissue and the most abundant; oxygen - 20% - utilized in respiration; argon, carbon dioxide, and water vapor - 1% make up the other part.
Test for carbon dioxide:
Give each student or group 1/4 glass of limewater or bromothymol blue solution and straws. Have the students blow into the glass for several seconds and note what changes they observe.
Ask students question of what they have observed? Then tell them if the limewater turned milky white, or the bromothymol blue solution turned yellow, carbon dioxide was present.
You may also want to follow this up with a teacher demonstration on the properties of carbon dioxide if you know a recipe for making it. Afterwards, discuss that carbon dioxide is an odorless, colorless gas that does not support burning. Also tell students that they may want to learn more about carbon dioxide and its effects on our environment from searching the WWW for information about the greenhouse effect. You may also point out that carbon dioxide is used by plants in the process of photosynthesis. It is the gas that we exhale into the air.
Also if you have a formula for making oxygen, you may want to demonstrate the properties of it. Or, you may explain that oxygen is necessary for respiration in animals. Organisms need oxygen to release the energy from their food. Oxygen is a gas that supports burning. Also tie in that nitrogen gas is used to make living matter. Plants and animals do not use nitrogen directly from the atmosphere. Plants obtain it from the soil. Animals obtain it from eating plants.
Discuss the concept of the layers of the earth's atmosphere by showing a model of the atmosphere on the overhead projector or by drawing a model on the chalkboard. Relate to them that the earth is surrounded by a blanket of air that extends 1000 km or 100 miles above its surface. The air molecules are trapped by the pull of gravity from the earth's surface. Therefore the air pressure on earth is greater.
Demonstrate how styrofoam balls can represent air molecules. Show high or low pressure of the air molecules by spacing the balls in a glass jar and by compressing them. For example, high pressure can be shown by pressing down on the balls, moving them closer together. Briefly describe each layer of the atmosphere. Point out that the atmosphere is separated into layers based on the temperature changes that occur from one layer to the next. As we go higher into the atmosphere, generally, the temperature drops and the air molecules get thinner. Most weather occurs in the troposphere.
Next have students make their own models, or draw pictures to reinforce the concepts. Have the students paste styrofoam packing pieces onto large oaktag in an arrangement that represents the molecules in each of the four layers of the atmosphere. Students will model how molecules in the bottom layer are tightly packed; whereas molecules higher up spread farther and farther apart.
Next, discuss how several factors affect the amount of radiation that is absorbed by the earth at different places. Begin by relating information about how the rays from the sun heat the earth's surface.
Next ask if students have noticed how the way sunlight hits the earth changes during the day. Have students perform a simple test to demonstrate this concept.
Have students use a flashlight and a sheet of black paper to observe different angles of light hitting the surface of the paper. Have them try different things like taping one end of the paper to the top of a table or desk. Then while holding the sheet of paper straight up and down, shine the flashlight directly at the paper. Then observe the size and brightness of the lighted area on the paper. Next, hold the flashlight in the same place, but slowly move the top of the paper away from the light without bending the paper. The light should hit the paper less directly. Have student notice the size and brightness of the lighted area.
Discuss which angle of light made the biggest lighted area.
Ask: If the light were sunlight, which direction would heat the paper the most? The angle that sunlight hits the earth causes different temperatures. Direct sunlight causes higher temperatures. Relate the concepts of how unequal absorption of radiation causes unequal heating of the earth's surface. Because the atmosphere is heated by the earth's surface, it too is heated unequally. Have students refer to the world map. Ask which places in the world would have higher temperatures? Why? Relate to them that places near the equator would have higher temperatures because the air near the equator is heated more than air near the poles.
Ask what other factors might affect the amount of radiation that is absorbed by the earth at different places? Relate to them that because the earth is a sphere, the sun's rays strike different places at different angles. Similar to what we observed with the flashlight experiment. Also, tie in that the tilt of the earth's axis brings day and night periods and its path around the sun.
Allow students to go outside to collect data to determine how surfaces affect air temperature. Hand out a thermometer to each group of four students if you need to economize. Have them prepare the thermometer by taping it to a meter stick so that the thermometer bulb is 10 cm above the bottom. Remind them to stand the stick straight up at each location and hold for two minutes or long enough for the liquid in the thermometer to stop moving. Afterwards, take a reading and record the temperature on the chart. Have them measure the temperature of the air over as many different surfaces as possible. Have them first make a prediction of the air temperatures. Then record the actual temperatures over surfaces such as the following: concrete, in the shade of a tree, in the shade of a building, grass, soil, etc.
Students can make a chart with the headings: location, surface, prediction of air temperature, and actual air temperature.
Students should record the temperatures of the air early in the morning, at midday, and in the evening for several days at the same time each day.
Create a discussion after each data collection period. Compare which surface air temperature was greatest, lowest, etc.
Optional: Students can make bar graphs of the air temperatures measured to show comparison at each location.
Have students use the internet and other sources to find as much information as possible to support the following question: What factors cause air temperature to increase in some places more than in others? Next, to economize, you may need to divide students into groups of four. Have students use the internet to find real time data in which to compare their area to at least five other areas spread out across the U.S. or the world. Examples of things to compare may include: Comparing the angle of sunlight by looking at a map, the temperature, number of daylight hours, type of ground cover, water sources, etc. Next have them chart their findings.
Keeping the same students in groups of four, have them choose a planet to compare its atmosphere to that of the earth's.
Students can construct a chart to record the types of gases, mean temperature, and mean pressure.
Have students use the information charted from the WWW and other sources to write a report describing what factors affect the amount of radiation that is absorbed by the earth at different places. They should be able to draw conclusions on what factors cause air temperature to increase in some places more than in others.
The Earth's Atmosphere And Temperature
Waverly High School
Waverly, NE atmosphere.
Key concepts: Layers and temperatures of the Earth's Radiant energy and the tilt of the Earth.
I began this activity by presenting the background information the previous day in a class lecture/discussion format. Throughout the laboratory we tried to reinforce the "Key Questions". The concepts of the atmosphere layers and temperatures can be very abstract but this series of activities seemed to really help the students out. The proverbial "lightbulb" went on for a number of students during this activity.
I have listed a couple of follow up activities in the write up if anyone would like to carry these concepts further. I hope others can get some good useage out of this laboratory.
This activity went pretty much like expected. We did not seem to have any trouble with students grasping the concepts and seeing the connections. The only modification was to let students work at their own pace. I originally had planned to do the carbon dioxide part of the lab in the first ten minutes but some students took three minutes and others took over fifteen minutes. So we had some students doing different activities at different times but it worked out just fine because those that finished early helped out the students that were taking a little longer.
Students seemed to enjoy the air temperature part of the lab the best. They enjoyed working with the tilting of the earth, how different surfaces had different temperatures, etc. Maybe they liked that best because they could go outside.
This activity worked real well so it was well worth the time and effort I had developing it. To see the expression on a students face when the "lightbulb" went on made it all worthwhile.
The students met the learning objectives I had set before the activity began. The papers they wrote on radiant energy from the Web showed this to me. I am very confident that they benefited from this because we did this activity in September and I still hear comments about the weather - this or that about the temperature, why they get hot in dark clothes on sunny days, etc.
This activity did not differ too greatly from the way I have taught it in the past. But I did include the internet this time because I had the capability to have the entire class get on the internet at one time.