I really do not understand how any can be athiests from thinking real hard about it. How can you think everything on this earth just happened?
From my understanding, to be athiest, this is pretty much how it goes.
There was a big bang or some event, the earth and sun appeared. Somehow water got on earth. Them somehow the suns energy made single cell organisms magically appear. At some point fish and sealife were spawned. Then vegatation. Then all sorts of animals. And anytime there was some gap or opportunity for life to appear to do something, such as clean and eat crap, eat dead bodies, etc, bacteria, insects, animals just happen to form to do those things.
Everything happened by chance, the right thing and right mystery mix to create it all. Yet with the billions of forms of life that happened by chance and the right mix of some comic or biological juice, we are unable ourselves to find this mix and remove the random chance from it, and create entirely new types of plant, animal, sealife, etc.
I understand why many may not believe in a God, or perhaps one described in any of our books. At the very least I think all would think that either a very highly intelligent life long ago created the life here on earth and just left it. (but where did they come from).
It seems to take more faith that everything happened by chance and there is no life behind the start of our life then it takes to admit we did come from something, whether any books or ideas we have on what we came from are correct or not can't be 100% proven at this time.