Hey cool, it is easy. First greet all the who are gathered there.
Then, start speaking this. 
Ozone layer is important for survival because ozone layer protects us from the harmful ultraviolet rays of the sun. Hence, it is important for our survival. The ozone gets depleted by the excessive carbon-dioxide and other green house gases emissions.
Then, u can say a story of a man who even uses motor bikes to go to a nearby shop, and pollutes the environment; and then you can say the statics of greenhouse gases emissions, and conclude by saying that,
Ozone layer is important for our survival. But, due to the excessive pollution, the ozone layer is getting depleted, which may lead to global warming. So, it is our duty to protect our defender. 
Then say, Thank you for giving me this opportunity to speak. 
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