the ozone layer

Back to SCIENCE main page

The Earth is surrounded by a deep layer of gas called the atmosphere. The atmosphere is a mixture of gases, including nitrogen, oxygen, carbon dioxide, argon and water vapour.

Oxygen

Plants use the energy in sunlight to make their own food by photosynthesis:

carbon dioxide + water → glucose + oxygen

In other words, photosynthesis releases oxygen into the atmosphere, and removes carbon dioxide. This reverses the effect of respiration.

Ozone

  Diagram of ozone layer protecting people below from harmful ultraviolet rays   Satellit photo of ozone hole above Antarctica
The ozone layer (blue) above the Earth protects living things from harmful ultraviolet rays.
This satellite photo shows up a gigantic hole (blue) in the ozone layer over Antarctica (South Pole). This hole is caused by industrial chemicals. Scientists are worried by this hole, because it lets through harmful ultraviolet rays and it might get bigger.

Ultraviolet light from the Sun provides the energy needed to make ozone, O3, from atmospheric oxygen, O2. Ozone absorbs ultraviolet radiation. This prevents it from reaching the ground and harming living organisms, especially animals.

Ozone layer

The ozone layer is the part of the atmosphere where most ozone is found - between about 15km and 40km above the Earth’s surface. The concentration of ozone there is still only around eight parts per million.

Diagram showing how ozone molecules are made and unmadeAbsorbing ultraviolet light

The ozone layer absorbs ultraviolet light from the Sun and prevents it from reaching the surface. This protects living things from its harmful effects.

The ultraviolet light splits oxygen molecules, O2, into separate oxygen atoms. These react with other oxygen molecules to make ozone molecules, O3. This is a reversible process.

 

 

[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science ]