That is a very good question! In short, there is no definitive answer to that question. There are many “theories” as to why they lived longer, but they cannot be proven positively. We do know this though, as time went on the lifespan of man became shorter and shorter. Genesis 5:3 tells us, “So all the days that Adam lived were nine hundred and thirty years; and he died.” Many of Adam’s children and grandchildren lived to be over 900 years old (see Genesis 5:4-32) but after the Flood in Noah’s day the average lifespan of man decreased by hundreds of years. Two notable examples of this are found in Abraham and Moses. Genesis 27:7 says, “This is the sum of the years of Abraham’s life which he lived; one hundred and seventy-five years.” In Deuteronomy 34:7 we learn that “Moses was one hundred and twenty years old when he died.

Because man’s lifespan was greatly reduced after the Flood, a popular theory known as the “canopy theory” has been adopted by many. One has explained it this way: “According to this theory, the water ‘above the firmament’ (see Genesis 1:7) created a greenhouse effect and blocked much of the radiation that now hits the earth, resulting in ideal living conditions. At the time of the flood, the water canopy was poured out on the earth (see Genesis 7:11), ending the ideal environment.”

Today the average lifespan is more in keeping with what we read in Psalm 90:10, “The days of our lives are seventy years; and if by reason of strength they are eighty years, yet their boast is only labor and sorrow; for it is soon cut off, and we fly away.” Is this due to the “canopy theory?” Most “creation scientists” reject this view and thus other “theories” have been advanced. One of those theories is based on the “spread of diseases.” In this view, there was a lack of serious diseases in Adam’s day, but as time went on various diseases came into existence which then spread throughout the world, resulting in the average lifespan of 70 years that we have today.

Again, these are only theories which may or may not provide the answer to your question. It is better to consider WHAT WE DO KNOW. We know that it was SIN that brought disease and death to the human race. “Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned” (Romans 5:12). We know that no matter what man’s lifespan has been, it is really SHORT. “For what is your life? It is even a vapor that appears for a little time and then vanishes away” (James 4:14). We know that death does not end our existence. “And as it is appointed for men to die once, but after this the judgment” (Hebrews 9:26). We know that if one hasn’t trusted in Jesus Christ for salvation they will spend eternity in hell. “Therefore I said to you that you will die in your sins; for if you do not believe that I am He, you will die in your sins…And anyone not found written in the Book of Life was cast into the lake of fire…These shall be punished with everlasting destruction from the presence of the Lord” (John 8:24; Revelation 20:15; 2nd Thessalonians 1:9). We know that if one has trusted in Jesus Christ as their Savior they will spend eternity in heaven. “For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life” (John 3:16). We know that for the saved in glory there will be no disease or death. “And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away” (Revelation 21:4).

Has my reader received eternal life by “believing on the Lord Jesus Christ?” If so, what a glorious future awaits you! Your life won’t be counted in days or years (for you will be in eternal glory with your Savior and all the redeemed). Instead, you will live forever in absolute bliss, as we saw from Revelation 21:4.  (354.5)  (DO)