HallsofIvy wrote in another thread: Just yesterday I was asking myself that very same question. So thanks for giving such a nice an simple explanation. I was also wondering why the atmosphere revolves with the earth; something you stated but didn't explained. Is it something that goes back to the time of the creation of the earth? Most unlikely imo. So what is the reason? And why is there an atmosphere in the first place? I.e. why doesn't it just fall down on earth like a decent piece of matter?