Antediluvian gravity was affected (practically) by the existence of a large body of water above the atmosphere, possibly like the rings of Saturn.
This is exactly what the Bible describes in the Genesis creation story, the story of Noah’s flood, and in Peter’s explanation of the change that occurred at the flood.
Genesis 1:7
Thus God made the firmament [i.e. sky], and divided the waters which were under the firmament from the waters which were above the firmament; and it was so.
Genesis 7:11
In the six hundredth year of Noah’s life, in the second month, the seventeenth day of the month, on that day all the fountains of the great deep were broken up, and the windows of heaven were opened.
2 Peter 3:5-6
For this they willfully forget: that by the word of God the heavens were of old, and the earth standing out of water and in the water, by which the world that then existed perished, being flooded with water.