The atmosphere is the layers of gas that surrounds a planet. So our atmosphere is comprised of mostly; Nitrogen, which helps form compounds and we essentially need it to grow, then their is Oxygen which we need to breathe air and function our internal organs, then Argon which does exactly have any good or particular use. Argon is the third most found gas in our atmosphere, then their is Nitrogen which would come in 2nd and Oxygen 1st out of the 3. I believe that a portion of the earths atmosphere is comprised of water vaporization since over 60% of the earth is water!