How does the Ozone Layer High in the Atmosphere Protect Life on Earth? — Reading Comprehension

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"This educational science passage, aligned with NGSS standards, explores the critical role of the ozone layer in shielding Earth from the Sun's harmful ultraviolet (UV) radiation. Designed for middle school students (grades 6-8), the text details the formation of ozone molecules (O3) in the stratosphere and explains how this natural process protects human health and ecosystems. It also covers the impact of human-made chlorofluorocarbons (CFCs) on the ozone layer, the discovery of the ozone hole, and the successful global response through the Montreal Protocol. The passage integrates key vocabulary and real-world connections to provide a comprehensive and engaging overview of this important environmental topic."

CONTENT PREVIEW

Earth's atmosphere, showing the ozone layer in the stratosphere absorbing harmful UV rays from the sun. — The stratosphere protects life by absorbing most of the sun's harmful ultraviolet (UV) radiation.

The ozone layer is a critical part of Earth's atmosphere, acting as a natural shield that protects all living things from harmful solar radiation. This protective layer is located in the stratosphere, a region of the atmosphere that sits high above our planet’s surface. It is composed of ozone (O3), a molecule made of three oxygen atoms. While ozone near the ground is a pollutant, the ozone layer high up is essential for life. Its primary function is to absorb most of the Sun's dangerous ultraviolet (UV) radiation, particularly the most harmful types, such as UV-B and UV-C rays.

The process of protection begins when high-energy UV radiation from the Sun strikes an oxygen molecule (O2) in the stratosphere. This energy splits the oxygen molecule into two separate, highly reactive oxygen atoms (O). Each of these single oxygen atoms then quickly combines with another oxygen molecule (O2) to form a new ozone molecule (O3). This continuous cycle of creation and destruction of ozone molecules is a delicate balance. As the ozone molecules form, they absorb the UV radiation, preventing it from reaching the Earth's surface in large quantities. This absorption is what makes the ozone layer so vital.

Without the ozone layer, the amount of UV radiation reaching Earth would be significantly higher. This would have devastating effects on ecosystems and human health. Increased exposure to UV radiation can lead to higher rates of skin cancer and cataracts in humans. For plants, it can damage cells and reduce their ability to perform photosynthesis, impacting crop yields and disrupting food chains. Marine life, especially tiny organisms like phytoplankton, are also vulnerable to UV radiation, which could harm the base of the ocean’s food web.

The discovery of the ozone hole—a dramatic thinning of the ozone layer, particularly over Antarctica—brought global attention to its vulnerability. Scientists linked this thinning to the use of human-made chemicals called chlorofluorocarbons (CFCs), which were once common in aerosol sprays and refrigerants. When CFCs rise to the stratosphere, they release chlorine atoms that destroy ozone molecules. International agreements like the Montreal Protocol have successfully phased out many of these chemicals, allowing the ozone layer to slowly begin its recovery. This global effort shows how human actions can both harm and help our planet.

Fun Fact: A 1% decrease in the ozone layer can lead to a 2% increase in the amount of harmful UV radiation reaching Earth's surface.

What is the primary function of the ozone layer?

To produce oxygen for breathing.To absorb most of the Sun’s harmful UV radiation.To help regulate the Earth's temperature.To create a habitat for airborne organisms.

What is an ozone molecule composed of?

Two oxygen atoms and one nitrogen atom.Three nitrogen atoms.Three oxygen atoms.Two oxygen atoms.

In which part of the atmosphere is the ozone layer located?

The troposphere.The mesosphere.The stratosphere.The exosphere.

According to the passage, what is a potential effect of increased UV radiation on plants?

Increased rate of photosynthesis.Damage to cells and reduced crop yields.Longer growing seasons.More efficient water absorption.

How does the Sun's energy help create ozone molecules?

It heats up oxygen molecules, causing them to bond.It splits oxygen molecules into individual atoms.It converts nitrogen into oxygen.It combines three nitrogen molecules.

What is the main idea of the provided passage?

The ozone layer is a natural shield that protects life from UV radiation.Ozone is a pollutant that is harmful to humans.The Montreal Protocol solved all problems related to atmospheric chemicals.The Earth's atmosphere is made up of many different layers.

How would the food web in the ocean be affected if the ozone layer were completely destroyed?

Phytoplankton would grow faster, strengthening the food web.All marine life would adapt to the higher UV radiation.Phytoplankton would be harmed, disrupting the base of the food web.The temperature of the ocean would rise, killing all marine life.

What type of human-made chemicals were found to be responsible for the thinning of the ozone layer?

MethaneCarbon dioxideChlorofluorocarbons (CFCs)Nitrogen oxides