Thank you for the question on the cause of diminishing age before and after Noah’s Flood, “What happened to the atmosphere and quality of the air after Noah’s flood in that Noah himself still lived to be 950 years old but Abraham didn’t make 200 and Moses even less?”
As one reads Genesis 5–10, the Scriptures record the limiting of the age of mankind. God said this in Genesis 6, “When human beings began to increase in number on the earth and daughters were born to them, 2 the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose. 3 Then the LORD said, “My Spirit will not contend with humans forever, for they are mortal; their days will be a hundred and twenty years…5 The LORD saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. 6 The LORD regretted that he had made human beings on the earth, and his heart was deeply troubled. 7 So the LORD said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.” 8 But Noah found favor in the eyes of the LORD.” (A searchable online Bible in over 150 versions and 50 languages). I trust the readers will re-read Genesis 5–10 to ponder more fully the Scriptural description of the Flood and its aftermath. The Scriptures does not state the cause or method by which God limit the age of humans to 120 years.
Here are some thoughts on the possible causes for the age limit of humans apart from God’s declaration causing some form of genetic mutation within human’s DNA.
A. The outer layer of water that shielded the atmosphere and land mass was diminished or depleted due to the unprecedented rainfall on earth. The loss of the outer layer of water would allow the sun’s ray to impact humans and life on earth. Decay became more rapid and genetic changes may have been accelerated on earth.
B. The outer layer of water that shield the earth from the meteorites impact were gone. The impact between the meteorites and the land mass or ocean would have adversely affected all life forms. The collision affected the atmosphere’s condition and temperature on earth.
C. The outer layer of water that fell on the earth was unprecedented as it may have caused land erosion and flooding that buried animals and vegetation. The loss of trees and plants could have impacted the air quality and water in the atmosphere causing change in wind patterns.
D. The upheaval of land masses as the submerged water from the crust of the earth was released on the earth could have affected wind patterns on earth. The formation of snow and dry arid land was due to wind patterns. With volcanic eruptions, ashes were hurled into the atmosphere affecting air quality.
E. The rapid releasing of underground waters and its drainage back into the earth would have affected the water quality of the ocean and the air. The saline of the ocean’s water may have affected that death of certain sea creatures. The land would be considered saline to some extent with the Flood and with the rainfall that fell after would have affect the water which humans drank from.
There may be other factors, but it is likely the air quality, wind pattern, and the formation of mountains affected all of life on earth. Personally I believe that God’s declaration of limiting the lifespan of man to 120 years was a genetic change that slowly occurred over generations as cell mutated or decayed within humans. The earth’s condition accelerated that decay. From what I read, geneticist thinks that they have discover the gene that causes aging. Whether geneticist can reverse the process or through medical technology, humans have the potential to live longer on earth.
God limited the age of man for it would be horrible to have a sexual predator or murderer live 200 to 700 years. The violence on earth can be horrific unless society begins to control human behavior through genetical engineering and brainwashing them. Can an old book, 1984, be true of us growing humans to serve the elite of society? Dictators have tried that by enslaving others and humanity is on the verge of genetically engineering people. Will society become better or worse? The record of human history is not good.
SUMMARY: God limited the age of humans to limit one’s violence on earth. One’s self-centeredness will drive him to control others for self preservation or self-exaltation of oneself.