Genesis 1:6-8 Then God said, “Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.” Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so. And God called the firmament Heaven. So the evening and the morning were the second day.
Here, God creates a global greenhouse. Making one more step closer to sustaining human life. God is very methodical in every day of creation. There was this vapor canopy shielding the earth from any dangerous cosmic rays and radiation. It was this water vapor canopy that would be a major contributor to the worldwide flood. God is so very wise.