Question

What key function does the atmosphere serve that enables life to exist on the planet?

Answer 1

Of course, the obvious one, oxygen. The atmosphere provides oxygen for us humans and animals to breathe.

It protects us from the radiation of the sun. Without it, the ultraviolet radiation could cause living cells, damaging our skin.

It also keeps the surface heat of the earth in. (The Greenhouse Effect)

Answer 2

I am pretty sure that the atmosphere keeps the oxygen and light in it