The ozone layer filters out incoming radiation in the "cell-damaging" ultraviolet (UV) part of the spectrum. Without ozone, life on Earth would not have evolved the way it has. The discovery of a large ozone hole over Antarctica and is association with man-made CFCs led the world to take action to protect the ozone layer.
Click Bart Simpson (left) for the easy-to-read young person's text and Mr. Burns (right) for the more technical information.