I read in your response “Decreasing Life Spans” your explanations of water vapor protection and electromagnetic fields being possible causes for the extraordinary (by our standards) life spans. I always thought that the post-Eden life spans were due to the lingering effect of Adam and Eve having eaten from the Tree of Life. In Genesis 3, God cited as one of the reasons He banned the couple from the Garden, His concern that they would continue to eat from the Tree of Life and live forever. I always assumed that the farther away from the Tree of Life the generations grew, the shorter their life spans became.
Before the fall Adam and Eve were immortal. They became mortal by disobeying God. They were banned from the Garden to prevent them from regaining immortality as sinners. With the exception of Enoch, life spans in the 800 year range continued until the flood, which came 1656 years after the Creation, and then began shortening dramatically afterward. It dropped to 500 years in the first post flood generation and by the time of Abraham, 8 generations later, it was down to 175. You can verify this by clicking here. Later life spans were even shorter. Jacob lived 130 years, Joseph 110, Moses 120, etc.