A careful consideration of the Genesis account reveals that events starting during one day continued into one or more of the following days. For example, before the first creative day started, light from the already existing sun was somehow prevented from reaching the earths surface, possibly by thick clouds. (Job 38:9) During the first day, this barrier began to clear, allowing diffused light to penetrate the atmosphere.*
On the second day, the atmosphere evidently continued to clear, creating a space between the thick clouds above and the ocean below. On the fourth day, the atmosphere had gradually cleared to such an extent that the sun and the moon were made to appear in the expanse of the heavens. (Genesis 1:14-16) In other words, from the perspective of a person on earth, the sun and moon began to be discernible. These events happened gradually.
The Genesis account also relates that as the atmosphere continued to clear, flying creaturesincluding insects and membrane-winged creaturesstarted to appear on the fifth day. However, the Bible indicates that during the sixth day, God was still in the process of forming from the ground every wild beast of the field and every flying creature of the heavens.Genesis 2:19.
Clearly, the Bibles language makes room for the possibility of some major events during each day, or creative period, to have occurred gradually rather than instantly, perhaps some of them even lasting into the following creative days.
Does Science Contradict the Genesis Account? — Watchtower ONLINE LIBRARY