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.
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.
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.
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
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