[esquirette]

Try this theory--there was a water canopy which encircled the earth, thus raising barometric pressure a lot, and filtering out damaging ultra violet rays, such that people lived a really long time. Then something happened, the fountains of the deep opened, and the water canopy in the sky rained down for forty days and nights, basically disappearing forever, the water level of the whole earth was raised several feet, and man no longer lived to be 500 years old.