That is simply not true.
Atheism is not dependent on any knowledge of science whatsoever, just a lack of belief in gods.
I don't believe in gods either and I'm not an atheist. But ontologically speaking, either the universe is eternal or it isn't. It is either the result of Intelligent purpose or it isn't. If it is not eternal then it had a beginning and then the question is, what is the sufficient cause of it? There are only a few possiblities. What choice other than some materialist explantion does a good atheist have to try to account for the existence of the universe?
Someone might be a practical atheist and may never have given the issue a thought, but I'm referring to the problem itself, not anyone's lack of thought about it.
Cordially,