It is commonly held that the pre-flood vapor canopy shielded the earth form cosmic radiation and also reduced surface ozone levels. These effects supposedly contributed to the longevity of the antediluvian patriarchs. However, radiation studies and research in molecular biology seems to rule this out. Even if the earth were 100 percent shielded from radiation and if ozone levels in the pre-flood world were zero, no appreciable improvement would have resulted. Studies in molecular biology, however, do suggest that possibly certain specific enzymes may have been present prior to the flood and absent afterward, their disappearance resulting in the reduction of longevity noted in the exponential decay curve of lifetimes in Genesis 11. Also, increased atmospheric pressure under such a canopy would conceivably have had a minor effect on longevity and also on gigantism.