Ozone Layer – Definition, Formation, Depletion & Effects

What is the Ozone Layer?

The ozone layer, also known as the ozone shield, is a region in the Earth's stratosphere that absorbs most of the Sun's harmful ultraviolet (UV) radiation. Although ozone (O₃) is present in small amounts compared to other atmospheric gases, it plays a critical role in protecting life on Earth.

Located roughly 15–30 km (9–18 miles) above the Earth's surface, this layer filters out the majority of UVB radiation, which can cause skin cancer, cataracts, crop damage, and harm to marine ecosystems.

History of Discovery

The ozone layer was discovered in 1913 by French physicists Charles Fabry and Henri Buisson. They found that while the Sun’s spectrum matched that of a hot body (around 5,500–6,000 K), ultraviolet radiation below 310 nanometers was missing — proof that something in the atmosphere was absorbing it. That “something” turned out to be ozone.

How Ozone is Created

UV light breaks oxygen molecules (O₂) into single oxygen atoms.
These atoms, being highly reactive, combine with O₂ to form ozone (O₃).
This process releases heat, warming the stratosphere.

How Ozone is Destroyed

Ozone bonds are weaker than those in O₂, so lower-energy UV light can break them apart. When destruction equals formation, the ozone amount stays constant — but human activities have tipped the balance.

Mechanism of Ozone Depletion

Main Cause – Human-Made Chemicals

The biggest culprits are chlorofluorocarbons (CFCs) and other halogenated compounds found in refrigerants, aerosols, and solvents. These compounds are:

Extremely stable in the lower atmosphere.
Able to reach the stratosphere over decades.
Broken down by high-energy UV photons, releasing chlorine atoms.

A single chlorine atom can destroy millions of ozone molecules through a continuous catalytic cycle.

The Antarctic Ozone Hole

Discovered in the 1980s, the ozone hole forms each spring over Antarctica due to:
- Polar vortex winds trapping cold air.
- Polar Stratospheric Clouds (PSCs) forming in extreme cold.
- Release of chlorine and bromine compounds when sunlight returns.
The hole size varies depending on polar vortex strength — stronger vortex years result in a larger ozone hole.

Effects of Ozone Layer Depletion

On Humans

Increased skin cancer and cataracts.
Weakened immune system.

On Marine Life

Damage to phytoplankton and zooplankton, the foundation of the marine food chain.

On Plants & Agriculture

Slower growth, reduced yield, and lower nutritional quality in crops.
Greater vulnerability to diseases.

On Animals

Eye and skin cancers in domestic animals.
Threat to young marine species like fish larvae and shrimp.

On Materials

UV radiation accelerates degradation of plastics, rubber, wood, and textiles, increasing maintenance costs.

Conclusion

The ozone layer is Earth’s natural sunscreen. Protecting it requires strict control of ozone-depleting substances — a goal addressed by global agreements like the Montreal Protocol. While recovery is underway, continued vigilance is essential to safeguard life on our planet.

Ozone Layer – Definition, Formation, Depletion & Effects