How is oxygen from atmosphere important?

The presence of ozone is important because it shields living organisms from some harmful radiation from the Sun.

As it happens, the vibrational frequency of the atoms in ozone matches that of UV light, consequently it protects organisms on earth by absorbing (in the upper atmosphere) most of the UV radiation before it hits people and other living things here on the surface. Unfortunately ozone in the lower atmosphere is actually harmful to most living things since it is very reactive. It irritates our respiratory systems and eyes as well as attacking cellular membranes of plants and participating in reactions that produce other types of pollution.