Having grown out of a young-earth Creationist religion, I can say that the 6000 year claim is based on a rather fanatically literal interpretation of Genesis an

Having grown out of a young-earth Creationist religion, I can say that the 6000 year claim is based on a rather fanatically literal interpretation of Genesis and the surrounding histories. Reading the genealogy of Genesis 5 and trusting that the ages are accurate, that they skip no one, and that Adam was literally created by God in year 0. With some simple addition, that genealogy gives a birth date for Abraham of about 2000 years after Adam. From there, a literal/historical/grammatical hermeneutic brings you to the Exodus and iron age histories that can pretty confidently assign real dates. Maybe it's just the indoctrination I grew up in that still empathizes with the ability to read "After Noah was 500 years old, he became the father of Shem, Ham, and Japheth" and say "yep, there's another 500 years on the chronology" and imagine that Christians have always done that.