Here are some reasons that we need the atmosphere.
1.Without the atmosphere there we would burn up because there would be no atmosphere to reflect the suns rays so the Earth would be to hot for use to survive.
2.Another reason is that there would be no ozone layer so there would be nothing to protect us from the meteors probably destroying the Earth .
3.Without the atmosphere there would be no air for us to breath so nothing could survive and the Earth would turn into a massive desert.
4.If there was no atmosphere there would no weather so again the Earth would turn into a massive desert.
5.With out the atmosphere the Earth would be to hot for a liquid like water to stay in liquid form instead of freezing or evaporating