A proof is usually some premises together with a conclusion, such that the premises are true or accepted, and it is not possible that the premises are true while the conclusion is not - usually for formal reasons.

I don't see why "life exists and no god exists" should be a contradiction for formal or other reasons.

Furthermore: the existence of which god? As you know there and have been many religions with different gods.

And lastly: if it was straightforward, how come so many people fail to see it?