As an aside, I can recall my high school religion class teacher confidently but foolishly asserting that Adam and Eve didn't exist, Abraham most likely didn't exist and Moses didn't cross the Red Sea but the Reed's Sea. It was the time of year, she explained, to justify the ability of the Hebrews to cross such a massive body of water. Being clueless teenagers, I don't recall that we questioned the teacher about how the Egyptians were swept away in an evaporated lake.
But back to Genesis 5...this passage boldly asserts the record from Adam to Noah and everyone in between. I'd like to focus on Methuselah, the longest earthly human life on record. Indeed, he could have been the longest lived human who ever lived.
Given the fact that pushing 100 years old in today's world in very rare, one has to wonder how in the world did Methuselah make 969 years. Furthermore, a little study of the chronology in Genesis chapters 5-7 leads to the fact that Methuselah died in the year of the Flood. Noah was Methuselah's grandson and Noah was born when Methuselah was 369 years old (see Genesis 5:25 and Genesis 5:28). Noah was 600 years old at the time of the Flood (Genesis 7:6);Methuselah died when he was 969 (Genesis 5:27). Forgive the analysis but I like to use my Accounting degree. By adding 369 to 600 we find that Methuselah was 969 in the year of the flood and also in the year of his death.
One might think that Methuselah died in the Flood, but according to Dake's Annotated Reference Bible, in the notes for Genesis 5:22 it is noted that Methuselah was named prophetically by his father Enoch. The name Methuselah means, "when he is dead it (the deluge) shall come." Given that the Bible is inspired and without error we can discern that Methuselah died just before and in the same year as the Flood.
A painting of Noah's Ark by American Edward Hicks per Wikipedia. Used under the Fair Use Rules of the U.S. Copyright Law.
However, I digress. The key question, "How did Methuselah and for that matter Adam, Seth, and Lamech (Noah's father; Methuselah's son) live so long?"
While I haven't taken a poll on that question or even done a focus group my hunch is that the average person would either scoff at Methuselah's age or pull out what I like to call the liberal preacher's explanation. This is that the years given are allegorical or the years at that time were different than they are now. Statements like this are not credible and don't hold water in the light of a reasonable interpretation of the Bible.
Personally, I think that something happened atmospherically after the Flood that sped up the curse of death that came upon mankind after Adam's sin. Having heard creation teachers on the subject, I believe that the most rational explanation of why people lived so much longer before the Flood was that the atmosphere was more hospitable to humanity, perhaps there was more water vapor and fewer damaging rays from the Sun got through to the earth's surface before the Great Flood leading to much longer life expectancy.
The whole concept of hyperbaric medicine gives further respectability to this hypothesis. Hyperbaric oxygen therapy (HBOT), according to the Wikipedia article on the topic, is the medical use of oxygen at a level higher than atmosperic pressure. The effect is the increased oxygen transport capacity of the blood. HBOT is used in treating everything from carbon monoxide poisoning to autism and skin grafts to certain types of hearing loss.
Without addressing HBOT in detail, the bottom line is that the changed atmospheric pressure theory is one reasonable explanation for decreased life spans after the Flood.
A review of the genealogy of Noah's descendants shows a rapid decrease in life span:
*Noah himself lived 950 years (Genesis 9:28),
*Shem (Noah's son) lived 600 years (Genesis 11:10-11),
*Arphaxad (Shem's son) lived 438 years (Genesis 11:12-13),
*Shelah (Arphaxad's son) lived 433 years (Genesis 11:14-15),
*Eber (Shelah's son) lived 464 years (Genesis 11:16-17),
*Peleg (Eber's son) lived 239 years (Genesis 11:18-19). It should also be noted
that according to Genesis 10:25, "the earth was divided" in his time, referring to
the dispersal of humanity at the Tower of Babel to the ends of the earth.
*Reu (Peleg's son) lived 239 years (Genesis 11:20-21),
*Serug (Reu's son) lived 230 years (Genesis 11:22-23),
*Nahor (Serug's son) lived 148 years (Genesis 11:24-25),
*Terah (Nahor's son) lived 205 years (Genesis 11:32),
*Abraham (Terah's son) lived 175 years (Genesis 25:7),
*Isaac (Abraham's son) lived 180 years (Genesis 35:28),
*Jacob (Isaac's son) lived 147 years (Genesis 47:28). Jacob, when asked how old he was by the Egyptian Pharoah, said in Genesis 47:9 NIV, "The years of my pilgrimage (he lived 17 years after that question per Genesis 47:28) are a hundred and thirty. My years have been few and difficult, and they do not equal the years of the pilgrimage of my fathers." Given Pharoah's curiousity it would be safe to assume that 130 was a very old age by that time in human history.
*Joseph (Jacob's son)lived 110 years.
And so, the trend aside from a few generational blips, was clearly toward a drastically reduced human life expectancy. Given the infallibility and inspired nature of God's Word and confirmed by the rational scientific idea that life could indeed be cut short by a reduced oxygen level in the atmosphere, the genealogies in the book of Genesis can be trusted to be literal and accurate. The decreased human life span is fundamentally a tangible manifestation of God's curse on humanity for Adam's fall and man's wholesale wickedness on the planet which caused the Great Flood of Noah's time.
