Without evidence to the contrary, an atheist (by denying a god) has to say that everything comes from nothing. Life comes from non-life. Order comes from chaos. Natural law comes from randomness. The effects are greater than the cause. These are all things anyone rejecting a form of theism must engage.
Now, Christianity certainly has unanswered questions. Not as many as people think, but they are there. I struggle with these, not because of a lack of faith, but because I am interested in knowledge.
Ultimately it may be that everything came from nothing, life came from non-life, order from chaos, natural law from randomness, and effects are greater than their causes. But man...you sure do have to have a lot of faith to believe that to be the case! It certainly seems much more reasonable, given the evidence, that an Intelligent Designer is responsible for these things.