I read somewhere, that there was a higher level of oxygen before the flood that would have contributed to longer lifespans.
I work in nursing in an environment that tends to be richer in oxygen due to constantly working oxygen tubes and vents as well as the tendency for unused o2 valves to be left on. I’ve had a theory for a while that the reason so many nurses in their 50’s look as young as they do is due to the increased oxygen in the environment.....it’s a pet theory and given that folks often say that I don’t look my age, I’ll just stick with that story!
There is some evidence that there was an ice canopy covering the earth, some distance up. The theory is that this ice canopy was shattered by a 'fly-by' such as an asteroid. As the ice fell it melted and produced the rain that was responsible for the flood. The canopy would explain the higher oxygen content, maybe exceeding 30%. the air trapped in pieces of amber has been analyzed and found to be in this range.