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Key Concepts

  • Why the atmosphere is important
  • Composition of the atmosphere
  • Air density and pressure

Lesson Objectives

  • Explain why Earth’s atmosphere is important.
  • Describe the composition of the atmosphere.
  • List properties of the atmosphere.

Lesson Vocabulary

  • air pressure: weight of the air pressing against a given area
  • altitude: distance above sea level
  • sound: form of energy that starts with a disturbance of matter, travels in waves through matter, and allows us to hear

Teaching Strategies

Introducing the Lesson

Help students recall what they may already know about Earth’s atmosphere. Go around the class, from one student to the next, and have each student state one fact about it. (Sample responses might include: the atmosphere contains gases such as oxygen, it surrounds the planet like a blanket, and it developed after the planet formed.) Tell students they will learn much more about the atmosphere in this chapter.


You may want to use the lesson plan at the following URL when you teach students about the composition and importance of Earth’s atmosphere. The lesson plan includes activities, a video, a reading, and an assessment.



Do demonstration #21 (“Why No Flood?”) at the URL below so students can observe the effects of air pressure. You will place an index card is placed over a glass full of water and then quickly turn the glass upside down. The index card should remain in place and the water should stay in the glass because the pressure of the air outside the glass is greater than the pressure of the water inside the glass. (You may want to practice the demonstration before showing it to the class.) Before you turn the glass upside down, ask students to predict what they think will happen when the glass is inverted. After the demonstration, challenge students to explain what they observed.


Differentiated Instruction

Have less proficient readers make a main ideas/details chart of lesson content. They should divide a sheet of paper down the center and list main ideas in the left column, leaving enough space between main ideas to add supporting details in the right column. Show students how to use the heading structure of the lesson to identify main ideas, and help them identify supporting details for the first main idea as an example.


Ask a few creative students to make a two- or three-dimensional model that represents changes in air density and pressure with altitude. Have them explain their model to the rest of the class, and then put it on display in the classroom.

Science Inquiry

Comparing Earth’s atmosphere with that of other planets will help students appreciate how Earth’s atmosphere affects its climate. In the modeling activity at the following URL, students will understand that our two closest neighbors, Venus and Mars, have very different atmospheres than Earth does in terms of air pressure and chemical composition. They will also be able to explain why Earth's moderate temperature is due primarily to its unique atmosphere. Included are assessment ideas and suggested modifications for differentiated instruction.


Common Misconceptions

A number of misconceptions about the composition of the atmosphere have been identified in students. Four of them are listed below. Provide students with counter evidence showing that each misconception is false.

  • The composition of air may vary from place to place.
  • Air and oxygen are the same thing.
  • Greenhouse gases such as carbon dioxide make up a major portion of the atmosphere.
  • The atmosphere contains only molecules of gases (no solid particles).

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Earth Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 15.1 Quiz in CK-12 Earth Science for Middle School Quizzes and Tests.

Points to Consider

In this lesson, you read that air density and pressure change with altitude. The temperature of the air also changes with altitude. Air temperature measures the heat energy of air molecules. What heats the atmosphere? Where does air gets its energy?

What causes the atmosphere to lose energy and become cooler?

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