Some oxygen molecules that contain two atoms absorb energy from the Sun's UV (Ultraviolet) rays and split to form a single oxygen atom. These single atoms mix with oxygen with two atoms and forms the Ozone layer.  

However pollution has caused the ozone layer to thin. This is a huge threat to life on Earth. Ozone depletion is particularly marked in the Antarctic Region. This is mostly known as the "Ozone Hole". Ozone Hole was discovered in 1948 by Jonathan Franklin, Joseph Farman and Brian Gardiner.

The ozone acts as the Earth's sunscreen; absorbing 98% of the damaging UV light. Chemicals called chlorofluorocarbons (CFC) are the primary culprits of the ozone layer breakdown. CFC gases are mostly produced by refrigerators, air conditioners and fire extinguishers. 

UV rays can cause damages in DNA, which may result mutation, ageing of the skin and skin cancers. 

Recognizing the effects of the ozone layer depletion, an international treaty, know as The Montreal Protocol was signed at Montreal, Canada in 1987. Which came effective from 1989 to control the emission of ozone-depleting substances. Many more efforts have been made and wearies protocols have been maid separately for developed and developing countries for reducing the emission of CFCs.