What is the atmosphere?
The definition of an atmosphere is a shield that protects Earth and other planets. Basically, it is just a bunch of gases that form together to make Earth a place for humans and animals to live in. The atmosphere is made of 78% nitrogen, 21% oxygen and 1% water vapour. Although, there are many other gases they are much too minute to calculate.
What does it do?
The atmosphere protects humans and it's inhabitants from the sun's harmful rays. The atmosphere also protects us from ultra-violet rays which can be very hurtful for humans. Ultra-violet radiation destroys living cells that help protect us from cancer. Although the atmosphere does not protect us from meteorites and meteoroids or anything that is going to hit the Earth. Hence, we are not safe from everything.