Apocrypha: Why People Before the Flood Lived Less Than 1000 Years

The apocryphal Book of Jubilees gives an intriguing explanation as to why Adam and many others before the flood lived less than 1000 years:

And [Adam] lacked seventy years of one thousand years; for one thousand years are as one day in the testimony of the heavens and therefore was it written concerning the tree of knowledge: “On the day that ye eat thereof ye will die.”