Being that no one from Earth has explored all that exists on Earth, much less space, I'd have to say that no one can be justified when they say Aliens don't exist. Nor can anyone be justified with saying they know how the Earth was created. Everyone from any side has their own ideas, beliefs and arguments. They all think they have proof. Real proof comes from tangible evidence. The fact of the matter is that evolution simply has much more tangible proof. God or no God, evolution wins in the proof area. Just my opinion.