As you know, in the past, our earth is very safety, it saved us from the sun light which is hamful for our health.
The sun light is contain untraviolet light which is divided into three types:
Uv-A: ( 400-325 nm ), Uv-B:(315-280nm), Uv-C (280-100), one of these types which is the most harmful for human is Uv-C, it causes skin cancer and many deseases.
the ozone layer which protect us avoiding untraviolet light from the sun, but it has been more and more destroyed by human. If we don't protect it, the human will be detroyed, so we need protect it by planting many trees and don't use CFCs gas.
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