I came to that conclusion after knowing the two following things:
1) The Bible is false.
2) Evolution is true.
To know that the Bible is false, you can read things like http://www.1001biblecontradictions.com/ or https://skepticsannotatedbible.com/
To know that Evolution is true, I would strongly recommend Cofty´s series of posts on it, they are brilliant, and also reading this book: https://www.amazon.com/Why-Evolution-True-Jerry-Coyne/dp/0143116649
Once you combine those two things, we are left with a tiny gap: Maybe there was a Creator that formed the first life, and then allowed it to evolve? But that gap is so tiny that it can easily be bridged and you can go ahead and just become atheist.
Because there are so many amazing things that are true and that are very complex that, once the first life started, came about via evolution and natural selection... so if all that can come from natural processes, then it is highly likely that the very first life also came from natural processes.