This post was originally written in May 2017 To navigate up to the Genesis index, see index-genesis.
There’s three major biblical traditions that give different chronological information for the book of Genesis: the Masoretic Text, the Samaritan Pentateuch, and the Septuagint. They give chronologies of Genesis that diverge by hundreds of years. You can find a chart that outlines these differences at the Wikipedia page Genealogies of Genesis.
In Protestant circles, the general practice has been to simply ignore everything but the Masoretic text most of the time. While I’m not at all confident that the Masoretic text has the “correct” genealogy (whatever that would mean given the ahistorical nature of Genesis), let’s just roll with the prevailing tide and deal only with the Masoretic Text today.
Genesis 11:10 states, This is the genealogy of Shem. Shem was one hundred years old when he became the father of Arpachshad, two years after the flood.
If you’re trying to construct a Masoretic chronology of Genesis, this is a problem. Here’s why. Genesis 5:32 states, When Noah was five hundred years old, Noah became the father of Shem, Ham, and Japheth. (Some translations do something different here, but I don’t think this can be justified. Perhaps I’ll discuss the translation of 5:32 at a later date.) So we can place the birth of Shem 500 years after the birth of Noah. Adding this date to Genesis 11:10, we conclude that Arpachshad was born 600 years after Noah.
However, Genesis 7:6 places the Flood 600 years into Noah’s life. Adding this date to Genesis 11:10, we conclude that Arpachshad was born 602 years after Noah.
Up to the birth of Noah, adding up the dates in Genesis is a straightforward task and results in 1056 years from Adam’s creation. However, Genesis provides two different dates for Arpachshad: either 1656 or 1658 Anno Mundi.
This is one of several places where the Bible gives multiple ways to find a date. This is why, for any date after Arpachshad, you can never say, “According to the Bible, event X occurred exactly Y years after Creation.”
There isn’t a biblical chronology. There are several biblical chronologies. Now, all of these are in the same ballpark: it’s clear that the Bible sees the world as being about 6,000-8,000 years old depending on the manuscripts and interpretations used. But there isn’t any agreement.