The ozone is a very important layer of the stratosphere. Ozone (03) is a chemical made up of 3 oxygen molecules, rather than the normal 2. It shields us from the ultra-violet rays of the sun. These UV rays are extremely harmful, and are responsible for global warming. The smog (carbon dioxide) in our atmosphere rises from our factories and reacts with the ozone, thinning the layer. Thankfully, in the years after this was discovered the Ozone has recovered somewhat. Efforts must be increased however, if we want the Earth to recover in time.
The ozone acts as a shield against harmful UV rays.