Did they really live that long in Genesis?

Did they really live that long in Genesis?
 

• So all the days of Seth were nine hundred and twelve years, and he died, (Gen. 5:7).
• So all the days of Enosh were nine hundred and five years, and he died, (Gen. 5:11).
• So all the days of Kenan were nine hundred and ten years, and he died," (Gen. 5:14).
• "So all the days of Mahalalel were eight hundred and ninety-five years, and he died," (Gen. 5:17).
• "So all the days of Jared were nine hundred and sixty-two years, and he died," (Gen. 5:20).
• "So all the days of Methuselah were nine hundred and sixty-nine years, and he died," (Gen. 5:27).
• "So all the days of Lamech were seven hundred and seventy-seven years, and he died," (Gen. 5:31).

     How is it possible for people to live that long?  Is the Bible correct about this especially since that our lifespan now, even with technology, is around 70 to 80 years. There are two possible explanations for the longevity of the early people of Genesis. 
     First, they were so close to the original genetic line of Adam and Eve, that there health was exceedingly great and so they could live this long. 
     Second, it is noteworthy that the lifespan of people drastically shortens after Noah's ark.  The theory is that there was a covering over the earth, a canopy of water vapor that helped shield the earth of harmful cosmic rays.  The Bible tells us that the firmament opened up and it rained for 40 days, covering the earth.  There is no biblical account of rain prior to this time.  Therefore, some theologians believe that after the flood, after the rain fell and the atmosphere lost a lot of its protective qualities, then the lifespan humans was drastically shortened