The ozone (o3) layer is the greatest protector of us from the harmful UV rays which comes directly from the sun. This ozone layers made a cover above us which deflects the ultra violate ray from coming to earth. Now now in many areas the ozone layer became holed, so from some area the UV ray arrived at the earth which causes skin cancer, and many other deseas which cannot be doctored. 
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The ozone layer is declining due to the CFC's released by us. ozone absorbs the harmful UV rays of the sun and minimizes its effect on us

due to its declining, the people are more prone to skin cancer, etc. as the UV rays can go through the skin and can affect the genes and causes cancer.

there is a big hole in the ozone layer above australia.