How could you be sure of the existence of a God, at first place.
How can you be so sure of the NON existence of a god? Science has its limits, the greatest of all scientists were philosophers and they believed in a single creator.
It only takes a single failed test to disaprove a tried and tested theory. The 'GOD' element cannot be tested because we can only test from what our limmited knowledge permits us within the confined aparatus, which is the world. GOD, is beyond that, therefore no test can prove it.
However if you are basing your conclusions based on the theory of evolution, then my friend I would advise you to search more into the subject. Evolution has been proven wrong time after time, not by religious scholors, but by scientists.