LESSON 1 - THE EARTH'S ATMOSPHERE
Objectives
Materials
Background Information
Key Questions
Vocabulary
Procedure
Evaluation
Objectives
- Students will define and compare the 5 layers of the atmosphere.
- Students will explain how the temperature of our atmosphere is measured.
- Students will explain what causes temperature differences in the atmosphere.
Materials
- bromthymol blue or limewater
- straws
- overhead projector
- foam packing peanuts
- large posterboard
- sheets of black construction paper
- flashlight
Background Information
Earth's atmosphere is the layer of gases surrounding the planet Earth and retained by Earth's gravity. It contains about four-fifths (78.084%) nitrogen and one-fifth (20.946%) oxygen, with trace amounts of other gases,
Minor (ppm):
Argon (Ar) - 9340
Carbon Dioxide (CO2) - 350
Neon (Ne) - 18.18
Helium (He) - 5.24
Methane (CH4) - 1.7
Krypton (Kr) - 1.14
Hydrogen (H2) - 0.55
Aerobic organisms use oxygen to release energy from food in a process called cellular respiration. Plants use carbon dioxide gas and water to produce sugars and oxygen gas during photosynthesis. Nitrogen is essential to nucleic and amino acids making nitrogen vital to life. Animals and most plants can not use nitrogen that is in the air. Legumes, soybean plants for example, recover nitrogen from the air because of nodules in their roots that convert ammonia to nitrogen during nitrogen fixation. Legumes then convert ammonia to amino acids and nitrogen oxides to form proteins. Animals get nitrogen from eating plants.
The atmosphere has no abrupt cut-off. It slowly becomes thinner and fades away into space. There is no definite boundary between the atmosphere and outer space. The temperature of the Earth's atmosphere varies with altitude.
- troposphere: extends from the surface to anywhere from about 4.5 to 10.5 miles, depending on latitude and weather factors, the temperature decreases with height.
- stratosphere: extends from the 4.5 - 10.5 mile range to about 31 miles, temperature increases with height.
- mesosphere: extends from the 31 mile height to about 50 to 53 miles, temperature decreases with height.
- thermosphere: extends from the 50 to 53 mile range to about 398 miles, temperature increases with height.
- exosphere: extends from the 398 mile height to about 5,965 miles.
Layers of the atmosphere image
Atmosphere table of heights
The troposphere is closest to Earth's surface. We live in the troposphere and this is where most of our weather occurs. The temperature decreases with height in this layer. In the troposphere layer, the sun heats the earth's surface, instead of the air. The air that is closer to Earth's surface is warmer than the air that is higher in this layer. Jets fly near the top of this layer.
The stratosphere is the atmospheric layer that is layered in temperature. It has warmer layers in its upper levels and cooler layers in its lower levels. This is opposite of the troposphere, that is cooler in its upper levels and warmer in its lower levels. The stratosphere has different temperature levels because the sun's ultraviolet radiation heats it from above. The ozone layer, about 12 to 31 miles high in the atmosphere, absorbs solar ultraviolet radiation, which heats up the top layers in the stratosphere. Commercial jet airliners generally cruise around a height of 6 miles, towards the bottom of the stratosphere. Most gliders ride on thermal plumes which rise up through the troposphere over warm patches of ground; these plumes end at the base of the stratosphere, setting a limit to how high gliders can fly in most parts of the world. The stratosphere also contains fast-flowing streams of air, jet streams, that circulate around the earth. They form at the boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air to the south. Because of the effect of the Earth's rotation, the streams flow west to east, resulting in a serpentine or wave-like manner at lower speeds than that of the actual wind within the flow.
The mesosphere has decreasing layers of temperature, which reach -118 to -135 F at a height of around 50 miles. In this region, levels of ozone & water vapor are almost nonexistent which causes the temperature in this layer to be lower than the temperature in the troposphere or the stratosphere.
The thermosphere is located above the mesosphere. The temperature here generally increases as it goes higher up. This increase is due to the intense solar radiation absorption by the lowlevels of molecular oxygen. At a height of 62 to 124 miles, the atmosphere is still made up of oxygen and nitrogen. At this altitude, gas molecules are very far apart.
The ionosphere is the part of the thermosphere and exosphere that is ionized by solar radiation. It has practical importance because it reflects radio waves which allows them to be sent around the world.
The exosphere is the highest atmospheric layer in Earth's atmosphere. The upper edge of the exosphere reaches to heights of 5,965 miles and is relatively unknown. The exosphere defines the boundary between our atmosphere and outer space.
There are different factors that affect how much radiation the Earth absorbs. The earth is round so the rays of the sun strike the earth at varying angles. The sun is directly overhead at the equator. The areas that are North or South of the equator are affected by the curvature of the earth and will not receive as much solar energy. Some of the other factors that affect how much of the sun's rays reach a specific location are the tilt of the earth's axis, whether an area is experiencing day or night, and the path of the Earth around the sun.
There is an uneven absorption of solar radiation which results in uneven heating of Earth's surface. Since our atmosphere is also warmed by the surface of the earth, it in turn is heated unevenly. The air around the equator becomes warmer than the air at the poles. Warm air expands. The heated air around the equator will not be as dense as the cold air near the poles. Air density determines the amount of force that is pressed down on the surface of the earth and is what is used to measure air pressure. Warm air exerts a lesser pressure than cold air does. Warm air is associated with low pressure and cold air is associated with high pressure.
Reflection and absorption of solar radiation image (NASA)
Latitudinal variations of solar radiation image (NASA)
Key Questions
- Explain what happens to the Earth's temperature throughout the day. Why do you think these changes occur?
- What causes air temperature to increase?
- How do different surfaces affect the temperatures of the air?
Vocabulary
- atmosphere
- troposphere
- stratosphere
- mesophere
- ionosphere
- exosphere
- temperature
- molecule
- ozone
Procedure
1. Describe & compare the different atmospheric layers. Start the lesson with leading questions to determine what the students know about the weather.
For example: What made you decide the type of clothes you would wear today?
Some of your students may answer "the temperature outside". Affirm that the weather outside often influences what we wear. Ask the students why they think we wear different clothes in the winter than we do in the summer. Some students may answer that the weather outside is different in the summer than it is in the winter. Ask your students to define weather. Explain to them that weather is the state of the atmosphere at a given time and place and is described in terms of temperature, moisture, wind speed, and barometric pressure. Reinforce the idea that our atmosphere is the air around us.
Demonstrate the chemical composition of air. Create a pie chart that represents the distribution of the four major gases found in the air:
Chemical composition of the atmosphere pie chart
Atmospheric composition (by volume, dry air):
-
Major:
- 78.084% Nitrogen (N2)
- 20.946% Oxygen (O2)
-
Minor (ppm):
- Argon (Ar) - 9340
- Carbon Dioxide (CO2) - 350
- Neon (Ne) - 18.18
- Helium (He) - 5.24
- Methane (CH4) - 1.7
- Krypton (Kr) - 1.14
- Hydrogen (H2) - 0.55
Water is highly variable, and typically makes up about 1%
Carbon dioxide test:
Distribute bromthymol blue solution or a glass of limewater and straws to your students or to each group of students. Have the students put the straw in the solution and blow into the glass for a few seconds and have them document the changes that they observe. Make sure that the students understand that they are not to blow so hard that the solution bubbles out of the container. Stress lab safety.
Begin a discussion about what they observed? Explain that a chemical reaction occurred that verified the presence of carbon dioxide in the air that the students exhaled through the straw. Carbon dioxide is the gas we exhale into the atmosphere. This was confirmed by the observation that the limewater turned cloudy and white, or that the bromthymol blue solution became yellow.
Follow up this demonstration with a discussion of carbon dioxide's properties. Explain that carbon dioxide gas is odorless and colorless and is not flammable. Direct your students to use the internet to explore carbon dioxide and its role in the greenhouse effect. Explain that plants use carbon dioxide for photosynthesis.
You may also wish to discuss oxygen and nitrogen gas using the information listed in the background information at the beginning of this lesson.
2. Draw a model of the layers of the atmosphere to use on an overhead projector or on the chalkboard. Explain to the students that Earth is encircled by a bubble of air that reaches 100 miles above the Earth's surface. Air molecules are held close to the Earth's surface by gravity.
Use the foam pieces to represent air molecules. You can demonstrate high and low pressure air molecules by placing the foam pieces in a glass jar and compressing them. High pressure can be demonstrated by pressing down on the foam pieces, which will move the molecules closer together. Explain that the atmosphere has distinct layers that are based on temperature differences. The higher the layer, the lower the temperature and the thinner the air.
Have your students paste foam packing peanuts onto a piece of construction paper so that they represent the spacing of the air molecules in each layer of the atmosphere. Students will demonstrate that molecules in the troposphere are very close together; and molecules in the thermosphere are spread far apart.
3. Discuss factors that affect how much radiation the Earth absorbs and how the sun heats the surface of the earth.
Ask your students if they have noticed that sunlight strikes the earth at varying angles throughout the day. Conduct the following experiment to illustrate this concept.
Have your students use the flashlight and black paper to simulate the rays of the sun striking the paper at varying angles. Have them experiment with the paper in different positions. For example, have them tape one end of the sheet of paper to their desktop and hold the sheet of paper in an upright position and shine the light directly onto the sheet of paper. Next, have them move the sheet of paper back, away from the light source, without bending or removing the paper from the desktop to create a different angle. Discuss which angle produced the largest area of light.
Explore the question, If the flashlight is the sun, which angle would produce the most heat? The angle at which the sun strikes the earth determines how much the temperature is affected. Direct sunlight produces higher temperatures. Remind your students that the earth is round, there are differences in the thickness of atmospheric layers, which creates an uneven absorption of solar radiation and in turn, creates hot and cold spots on the earth. Also, our atmosphere is heated by ground temperatures, which affects the heating of the atmosphere. Refer to a world map and ask your students to identify areas of the world that would have high temperatures. Explain that areas close to the equator are hotter because the air in this area is heated by a more direct angle of sunlight than areas near the poles.
What else might contribute to the amount of solar radiation that the earth absorbs? Possible areas of exploration could include the fact that earth is a sphere, earth's rotation creates periods of night and day, and the tilt of the earth's axis.
Send your students outside to test the air temperatures of different materials. Distribute a thermometer to each student or each group of students. Tape the thermometer to a stick four inches from the bottom. Have the students make a prediction of the temperature before they actually test the area. Make sure the stick is perpendicular to the ground at each location and hold the thermometer in place for at least two minutes, or until the mercury stops moving. Have the students record the temperature reading. Record as many different areas as possible. Some suggestions are concrete in the sun and shade, soil, shaded and not, metal, grass, etc. Have your students record temperatures at different times of the day for several days. Make sure they take the temperature readings at the same times each day.
Students will create a chart using the headings: location, time, surface, prediction, actual air temperature.
Generate a discussion to compare which surface area temperatures were highest, lowest, etc and possible explanations for the differences.
Optional Lesson: Students will generate bar graphs of air temperatures from different US cities.
Using the internet, find the information necessary to answer:
What factors would cause air temperatures to be elevated in some areas of the earth more so than in others?
Have your students form groups and access the internet to record real time data to compare their local area to five other cities in the US.
Examples of data to compare will include:
- sunlight's angle (by using a map)
- temperature
- daylight or night time hours
- ground cover
- near water sources
Have your students graph their data.
Have your student groups research another planet and compare its atmosphere to earth's.
Have your students create a chart recording the data they discover.
Evaluation
Have your students use information obtained from the internet to write an essay explaining the factors which affect how much solar radiation the earth absorbs at different locations.
