And on the second day, God took the waters and separated them, calling the top - sky.
As the planet was being prepared for habitation, I like to think there was a lot more going on here. Oxygen that we would need to breath came in-between the waters. Carbon dioxide that would interact with plants to replace the oxygen we used. . . I think a lot on the periodic table appeared on day 2.
Again, in comparison with other days of the creation week, this looks like a light day - but as a painter sands and prepares his surface for the undercoat before applying the finish, so it seems God was priming this earth for some very special creation in the coming days.