Genesis 5: 3-83 When Adam had lived 130 years, he had a son in his own likeness, in his own image; and he named him Seth. 4 After Seth was born, Adam lived 800 years and had other sons and daughters. 5 Altogether, Adam lived a total of 930 years, and then he died.
6 When Seth had lived 105 years, he became the father[b] of Enosh. 7 After he became the father of Enosh, Seth lived 807 years and had other sons and daughters. 8 Altogether, Seth lived a total of 912 years, and then he died.
There are a few theories that support the longevity of Adam and that lineage, so let’s look at a few of them.
The First possibility would be that they were so near to the original genetic decent of Adam and Eve, allowing their health to be amazingly great.
The second possibility was the food consumed was much healthier then as opposed to now. The soil’s quality would have been very high in nutrients.
Another theory is that there was a covering over the earth, a canopy of water vapor that helped shield the earth from harmful cosmic rays.
Genesis 1: 6 6 And God said, “Let there be a vault between the waters to separate water from water.” 7 So God made the vault and separated the water under the vault from the water above it. And it was so.
Finally there is another (unlikely but plausible) reason, and that is that time was measured differently. One possibility is that the Earth rotated faster than it does now.
The Bible says that the firmament opened up and it rained for 40 days, covering the earth. Therefore, some theologians believe that after the flood, the atmosphere lost a lot of its sheltering qualities and the lifespan of man was decreased severely by opening humans up to certain disease, which may have been absent before the flood?
The truth is we don’t know for certain how Adam, Seth and others had lived so long. We must take it as the Word of God and trust him.