Question

If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now?

Answer 1

It will be scorching hot in the day and extremely cold at night plus the UV rays will kill every single complex organism...the atmosphere is what protecting all the living beings from the freezing space and hot sun's rays... the compounds of carbon traps the heat inside and doesn't let most of the sun's heat reach us thus making earth an almost isolated object.
Yeah I guess we should thank the atmosphere...
hope this answer helps u :)