Chapter 8
The Ozone Layer
By Susan Stempleski
This chapter focuses on the theme of ozone depletion. The 50-minute lesson begins with a warm-up activity in which students explore the phrase "ozone layer". Then, working in pairs, students share their prior knowledge of ozone-related issues by taking a brief Ozone Quiz. Students then read and discuss a short article, All about Ozone, and re-evaluate their answers to the quiz. Next, students participate in a class discussion that encourages them to reflect more deeply on the problem of ozone depletion. Finally, if time allows, students can write a few sentences summarizing their own ideas about ozone depletion and what, if anything, they feel should be done about it.
Through reading about and discussing the topic of ozone depletion, students improve their language skills as they learn and use new vocabulary and concepts related to the topic. Some teachers may choose to present the activities described in the section on Classroom Applications in a single 50-minute lesson. Others may wish to combine the activities with some of the materials outlined in the section on Internet Resources to create a longer lesson or a unit of several related lessons.
Ozone Depletion
The ozone layer is a thin shield in the upper atmosphere that protects life on Earth from the sun’s ultraviolet (UV) rays. In the 1980s, scientists discovered that the ozone layer was being depleted. This depletion allows more UV radiation to reach the Earth’s surface. This is dangerous because overexposure to UV radiation can lead to very serious health problems, such as skin cancer and cataracts
"Good" and "Bad" Ozone
Ozone naturally occurs in two layers of the atmosphere: the troposphere and the stratosphere. The troposphere is the layer that surrounds the Earth’s surface. The ground-level ozone in the troposphere is "bad" ozone. It is an air pollutant and contributes to urban smog. The stratosphere is above the troposphere. The ozone in the stratosphere is "good" ozone. It protects life on Earth by absorbing some of the sun’s UV rays. When people talk about the "ozone layer," they are usually referring to the "good" ozone in the stratosphere, which lies between 10 and 20 miles (15 and 30 kilometers) above the Earth.
The Causes of Ozone Depletion
Until recently, chlorofluorocarbons (CFCs) were used widely in industry and elsewhere as refrigerants, insulating foams, and solvents. In fact, they are still widely used in air conditioners, refrigerators, and in some kinds of plastics. Strong winds carry CFCs into the stratosphere in a process that can take as long as 2 to 5 years. When CFCs break down in the stratosphere, they release chlorine, which attacks ozone.
What is Being Done About the Problem?
Countries around the world have recognized the problem of ozone depletion. In 1987 governments around the world signed a treaty called the Montreal Protocol to phase out the production and use of ozone-depleting substances.
