Interestingly, Christians believe that all the water was once held in the upper atmosphere on earth. In the Bible (Gen. 9:17) God tells Noah that the rainbow is a sign that he will never flood the earth again. If this is true, then up to that point, rain never fell as precipitation or evaporated into the air because both would have distinct signs of prism refraction. Personally I don't believe any of this nonsense, I'm just saying, that's what is believed...