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What is the ozone layer and why is it important?

Class 10 ScienceNCERT chapter: Our Environmentइसे हिंदी में पढ़ें

Exam-ready answer

The ozone layer is a region of the atmosphere rich in ozone (O3) that absorbs most of the Sun's harmful ultraviolet (UV) radiation. It protects living organisms from skin cancer, cataracts, and damage to crops and marine life. Thus, it is essential for the survival of life on Earth.

Explanation

The ozone layer is a layer of ozone gas (O3) present in the upper atmosphere (stratosphere). Ozone is formed when oxygen molecules (O2) absorb UV radiation and split into oxygen atoms, which then combine with O2 to form O3. This layer acts as a shield, absorbing about 97–99% of the Sun's harmful ultraviolet (UV) radiation.

Ozone is important because UV radiation can cause skin cancer, cataracts, and weaken the immune system in humans. It also damages plants, reduces crop yields, and harms phytoplankton in oceans, affecting the food chain. Without the ozone layer, life on Earth would be exposed to dangerous levels of UV rays.

However, human activities release chemicals like chlorofluorocarbons (CFCs) used in refrigerators and fire extinguishers, which deplete the ozone layer. This creates an ozone hole, especially over Antarctica. International agreements like the Montreal Protocol have helped reduce CFC emissions, and the ozone layer is slowly recovering.

Points to remember

  1. Ozone layer is in the stratosphere and contains high concentration of ozone (O3).
  2. Ozone absorbs harmful ultraviolet (UV) radiation from the Sun.
  3. UV radiation causes skin cancer, cataracts, and damages plants and marine life.
  4. Ozone depletion is mainly caused by chlorofluorocarbons (CFCs).
  5. Montreal Protocol is an international treaty to phase out ozone-depleting substances.

Exam tip

Draw a labelled diagram showing the ozone layer in the stratosphere and the ozone hole. Write the chemical equation for ozone formation and mention the harmful effects of UV radiation.

Questions students also ask

What is the ozone hole?
The ozone hole is a region of severe ozone depletion in the stratosphere, mainly over Antarctica. It is caused by human-made chemicals like CFCs. The hole allows more UV radiation to reach Earth's surface, increasing health and environmental risks.
How is ozone formed in the atmosphere?
Ozone is formed when high-energy UV radiation splits oxygen molecules (O2) into two oxygen atoms. Each oxygen atom then combines with another O2 molecule to form ozone (O3). This is a continuous process in the stratosphere.
What are the effects of ozone depletion?
Ozone depletion leads to increased UV radiation reaching Earth, causing skin cancer, cataracts, and weakened immunity in humans. It also harms plants, reduces crop yields, and damages phytoplankton, disrupting marine food chains.

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