Learners develop skills for thoroughly exploring STS issues as they apply those skills in investigating the focusing STS question. These include the study of science and social studies concepts or aspects of technology that are foundational to understanding the STS issue, through library research using primary and secondary sources, securing data and information from outside agencies, hands-on inquiry activities, collecting natural science data on site, and using social science research techniques such as questionnaires and interviews to collect data within the community. The information and data from the investigations are consolidated by learners to answer the STS focusing question.

Title: The Atmosphere

Overview & Outcomes:

In the last lesson, Foundations/Awareness Lesson 11, students identified three STS issues that fall under the umbrella of global atmospheric change (GAC) and requested information from outside agencies. In the next 15 lessons included in this the second or Investigations Section of the unit, student will carry out investigations on the STS question, "Is global atmospheric change a threat?" in order to develop an in-depth and multifaceted understanding of GAC in preparation for making informed decisions and taking appropriate actions in the last section of the unit. Students will begin their study of the atmosphere in this lesson by examining the composition and structure of the atmosphere. This information will serve as a base for all future discussions of GAC. Investigations Lesson 2 introduces students to the electromagnetic spectrum (EMS), which is another big idea basic to understanding GAC.

This lesson helps learners:

• Identify the four "spheres" (layers of the atmosphere) that operate and interat on the earth.
• Identify the many vital functions the atmosphere performs with regard to the support of life and temperature regulation.
• Describe the composition of the atmosphere.
• Describe the layering of the atmosphere around the earth, including the distribution of ozone.
• Recognize that the composition of the atmosphere has remained relatively constant through time.

The concept map shows model relationships among concepts this lesson seeks to develop. Concepts introduced in this lesson are bolded on that concept map and concepts from other lessons are in plain text (not bolded).

Background Notes for the Teacher:

Content. We can think of the earth as being composed of four interacting systems: atmosphere, hydrosphere, lithosphere and the biosphere. The first three are abiotic or non-living, which the biosphere is comprised of living matter.

The Atmosphere is comprised of gases: nitrogen (N), oxygen (O), argon (Ar), carbon dioxide (CO2), , water vapor (H2O) and trace gases. ( More detailed information is given later in this section.) The hydrosphere is composed of water in its solid, liquid and gas forms. These may exist in the atmosphere, on the earth's surface, and in the earth's crust.

The ware may exist as salt or fresh water. The lithosphere is earth's crust and a portion of the upper mantle, it is brittle and it moves (plate tectonics). The biosphere contains all living organisms and the environment in which they live. The biosphere overlaps with the abiotic spheres, as it covers from the sea floor to about 8 Km (5 miles) into the atmosphere. When thinking in terms of these four spheres, it is important to understand that there boundaries are not distinct, and they may overlap.

The atmosphere is not only a very essential component of the biosphere, but a very dynamic part as well. The dynamic, multifaceted nature of the atmosphere is often not completely understood by students. This lesson is intended to provide an information base for several future lessons. Students will not only study the composition and structure of the atmosphere, but also come to "appreciate" the many functions of the atmosphere as well as its constancy through time.

Function of the atmosphere-The atmosphere is often difficult to appreciate given the fact that on a clear, calm day, its presence is almost undetectable as are the essential gases it is composed of. The following is a brief list of atmosphere functions, most of which are necessary to support life:

• reservoir of oxygen (for respiration)
• reservoir of carbon dioxide (for photosynthesis)
• reservoir of nitrogen gas (necessary component of various organic compounds)
• temperature regulation
• protection from ultra-violet radiation
• protection from small meteors
• necessary for transmitting sound
• necessary for movement of flying animals such as birds and insects and of aircraft

Composition of the atmosphere-Many of the physical and chemical processes that occur in the atmosphere are directly related to its composition. The atmosphere is now composed almost entirely of oxygen and nitrogen in their diatomic forms (two atoms bound together by chemical forces). However, it was not always this way. When the earth formed about 4.5 billion years ago it probably did not even have an atmosphere. While the evolution of the atmosphere is not included in this lesson, it is interesting to note that once photosynthetic organisms evolved (beginning approximately 3.5 billion years ago), the atmosphere changed significantly. As oxygen (O2) was produced by these organisms, it built up in the atmosphere, as did ozone (O3). By about 400 million years ago, the atmosphere contained as much oxygen as it does today and overall, the proportion of gases in the atmosphere has remained about the same. This is an important feature of the atmosphere. It is vital that students understand that the relatively stable composition of the atmosphere is essential to its stable function.

The following table and pie graph provide basic information about the composition of the atmosphere:

The concentration of the "trace" gases (those occurring in amounts less than 0.1%) can also be given in parts per million rather than in parts per 100 (per cent). The most abundant of these is carbon dioxide at 340 parts per million (ppm). Interestingly, ozone concentration varies with altitude, reaching a maximum of 12 ppm at approximately 30 kilometers. It is important to note that even though there are only "traces" of certain gases, their concentrations are very important to living things and to the function of the atmosphere. For example carbon dioxide, water vapor, ozone and methane are "greenhouse gases-they absorb heat from sunlight at an average temperature of 53oF is a greenhouse gas-and ozone protects us cancer causing from UV light. In identifying the gases that make up the atmosphere, many sources refer to the composition of "dry air." This is due to the fact that the composition of dry air is remarkably constant over the globe, while the amount of water vapor varies widely, ranging from 4% by volume to less than 1%.

Structure of the Atmosphere-Meteorologists divide the atmosphere into four layers: the troposphere (where 90% of the total mass of the atmosphere and where almost all of the earth's weather occurs), stratosphere, mesosphere and thermosphere. The exact height of the atmosphere has no real meaning, for the air gets thinner and thinner the higher one goes and eventually thins out to outer space. Air is more compressed at sea level than at higher altitudes similar to feathers in a huge pile. What's at the bottom is more "squashed" than what's near the top. The division into layers is based on temperature and each layer has a different temperature range and profile. Temperatures decrease with altitude in the troposphere and mesosphere and increase with altitude in the stratosphere and thermosphere. These temperature layers are created primarily by the selective absorption of electromagnetic energy (which is discussed in Investigations Lesson 5). The following chart and graphic provides basic information about each of the layers:

Location of the Ozone Layer-Ozone (O3) is a molecule composed of three atoms of oxygen-a tri-atomic form of oxygen. Ozone is highly reactive with other atoms and molecules, and it acts as a filter for cancer causing UV light. Ozone absorbs the UV (shorter) wavelengths of sunlight and re-radiates the energy in the form of infrared (longer) wavelengths of light. In the process, the more common di-atomic form of oxygen (O2) is broken down forming non-atomic oxygen (O), which combines with other diatomic molecules of oxygen to form ozone (O3).

While the function of the ozone layer will be discussed in Investigations Lesson 4, the location of the ozone "layer" is an important idea to address in this lesson. Many sources describe the ozone layer as a band found in the stratosphere at a height of approximately 15 miles (25 km). However, in actuality, ozone molecules are found throughout the atmosphere but are "concentrated" in a broad band beginning at approximately 10 miles (16 km) and extending into the mesosphere to about 50 miles (80 km). While it is true that the ozone layer, if compressed, would be approximately 3 cm thick, it is inappropriate to refer to it as a thin band in the stratosphere. Tropospheric and stratospheric ozone will be distinguished and discussed at length in future lessons.

Additional Teacher References. Earth science texts and encyclopedias are good sources of additional information, diagrams, tables, charts and explanations about the atmosphere. If you do not have one, check with an earth science teacher in your district.

Materials:

For class.

1. Bulletin board or storyboard materials
2. Length of string (at least 4 feet) and chalk

For each student.

1. LAYERS OF THE ATMOSPHERE Worksheet (if desired).
2. Materials to make drawings or representations of the composition and structure of the atmosphere.
3. Materials to make pie charts or graphs representing the percentage composition of the gases found in the atmosphere.

Preparation:

Prior to day of lesson. Assemble bulletin or storyboard materials (see Appendix D). Duplicate worksheet (if desired). Assemble other appropriate student materials.

Instructional Procedures: (1 Day, 40 minutes)

1. Begin this lesson by helping students to understand how very thin the atmosphere is in relation to the size of the earth. Tie a piece of chalk to a length of string (over 4 feet long). Standing next to the chalkboard and placing your foot on the free end of the string, draw an arc on the board that has a 4 foot radius. The arc represents the surface of the earth.

2. Ask students to suggest how far the atmosphere extends above the surface. Students will typically guess anywhere from a few inches to several feet. Tell students that 90% of the earth's atmosphere is within about 10 miles of the surface.

3. The scale of this drawing is 1 foot = 1000 miles. The earth from the center to the surface is about 4000 miles. So on this scale, 10 miles is about 1/8th of an inch, which is about as thick as a chalk line. In other words, about 90% of the earth's atmosphere lies within the thickness of the chalk line used to draw the earth's surface.

4. At this point you can add that while the Space Shuttle orbits well above the atmosphere, using this scale, the Shuttle would only be about 2 inches above the surface.

5. Another way to explain how thin the atmosphere is is to imagine the earth shrunk to the size of an apple. The atmosphere would be as thin as the skin of the apple.

6. Keeping in mind the lesson outcomes and using the Background Notes for the Teacher, organize the lesson in such a way as to most effectively present the information provided. It is suggested that a bulletin board or storyboard be used in order to present the information in the most visual manner possible. This visual presentation can then be used throughout the Investigation portion of the unit. A worksheet (Structure of the Atomosphere) is provided, however students could also make their own drawings or representations of the atmosphere. By using a piece of graph paper, students can approximate the width of each layer of the atmosphere. Concept mapping can also be used as a presentation strategy (see appendix on concept mapping and example concept map set forth under "overview and outcomes" in this lesson).

7. Depending on their grade level, students could label pre-made pie charts or graphs or construct their own charts/graphs representing the percentage composition of the gases of the atmosphere. (Option: the pie charts may be generated by the students using a computer graphing or spreadsheet program, e.g., ClarisWorks.)

8. In representing the ozone layer on the bulletin/story board, it is important to illustrate ozone as a molecule mixed in with the other molecules making up the atmosphere. One way to accomplish this might be to use a colored background (blue for example) to represent the atmosphere and a "see-through" type of material such as tissue paper (white perhaps) laid over the background to represent the more concentrated area of ozone.

Assessment/Portfolio Items:

Journal Entry

Project

Student constructed or completed Pie Charts or Graphs representing the composition of the atmosphere.

Other

Concept map (individual and/or class)

Click Here to go to Investigations Lesson 2: EMS: Visible and Invisible Light