Its funny I remember discussing this with my father when I was a teenager, its always amazes me how science based on things as they are now think they can determine the way things were in the past, I told my father I believe there use to be a firmament that is why in the days before Noah people lived for hundreds and hundreds of years, then the firmament(even if this firmament was gaseous liquid clouds) gave way we had the flood and now increased radiation shortens our lives. theories are a dime a dozen, like carbon dating based on what, current carbon levels
I agree, in that something made them live longer, and it was, in my limited understanding, some sort of water canopy above the Earth, which would filter harmful radiation. At the time of the flood, it collapsed, and along with the fountains of the deep, flooded the entire Earth.