There is a layer in the upper reaches of atmosphere called ozone layer which is made up of triatomic oxygen molecules called ozone O3, which is highly poisonous and unsafe when compared to diatomic oxygen made up of 2 oxygen atoms which is highly essential for the living organisms survival. But this ozone layer is not stable to our earths surface and hence we are safe from this poisonous layer. Even though ozone is poisonous it performs an essential function where it is found. It absorbs harmful radiations from the Sun. This ozone layer prevents those harmful radiations from reaching the surface of the Earth where they may damage many forms of life.
Thus ozone even though not stable nearer to earth's surface it performs an essential function in protecting many forms of life on earth from harmful radiations from sun.
Due to usage of chloroflurocarbons by humans this ozone layer is getting depleted allowing harmful suns radiations to enter earths surface near Antarctica. Recently people are working towards stopping all further damage to the ozone layer.
