Ozone absorbs ultraviolet radiation that comes to earth from the sun.

UV radiation causes damage to the living cell. Without ozone we would all suffer from cell damage as the UV radiation would not be absorbed but instead would stream all the way down to the surface.

An ozone molecule is made up of three oxygen atoms in a chain. The ozone layer is a layer of ozone molecules scattered between 19 and 30 kilometers (12 to 30 miles) up in the earth's atmosphere. The concentration of ozone in the ozone layer is usually under 10 parts ozone per million.

Without the ozone layer, UV radiation would not be stopped from entering the earth's atmosphere and coming to the surface.Ultraviolet light can break chemical bonds of the molecules in cells. It is ultraviolet light that causes sunburns. If there were too much ultraviolet light around, our skin would burn very badly without any time for it to heal. If the ultraviolet light gets past the skin and gets absorbed by cells further in the body, those cells, and their DNA and other proteins, could also be damaged.

In the 1970's, scientists first discovered that chlorofluorocarbons(CFC's) potentially could destroy the ozone layer, and since CFC's had been in use as refrigerants, coolants, and propellants for aerosol cans since the 1930's, there was a lot of work that needed to be done.

Man-made chlorofluorocarbons(CFC's) are a large concern when it comes to the ozone layer. The long life of CFC's is one of the components that make them so hard for the ozone layer to handle. CFC's have a lifetime of about 20 to 100 years, before they get destroyed in the atmosphere. With a long life time like that, one CFC molecule can do a lot of damage, destroying ozone molecules for a long time. Even if we released no more ozone-harmful chemicals like CFC's into the atmosphere, the damage to the stratospheric ozone layer would continue for years to come.

If everyone on Earth stopped making, using, or releasing CFC's today, in what year would the existing CFC's in the atmosphere be destroyed. What would happen to the ozone layer after that?

The ozone hole over Antarctica is growing every day. Now it is about 8.3 million square miles in size during the winter months, large enough to cover most of North America, and most of the damage to the ozone layer comes from human activity. We account for between 75% and 85% of the ozone depletion that takes place each year. 1% to 5% comes from volcano eruptions each year and 15% to 20% from other natural sources.

How do volcano eruptions cause changes in the ozone layer?
Sources:
click here (The EPA site is excellent. It has answers to many of these questions, and lots more! It has information on methyl bromide too.)