Moses stated that the Almighty ordered that there should be light. Scientists write volumes explaining how, when the mass of water became too heavy, it fell back upon the earth, submerging it in a sea which reached almost, if not quite, the boiling point. As the land masses cooled they shrank greatly, and the depressions formed the beds of seas, while the highest points lifted above the water. When the crust and seas cooled, through untold periods of time, the vapor was not thrown up, and light could penetrate to the earth.

There is a possibility that Moses recognized that this was what had happened, and upon it he based the story of Noah and the ark. Or traditions of such a period in the earth's history may have been handed down by students before his time, or there could have been a great flood as described, that covered all the then known surface of the earth.

From What Moses Taught About The Beginning Of The Earth