I already said some of it comes from the Babylonian captivity. That’s why we have two versions of the same creation story told back to back, and two different versions of Noah’s flood.
I’m not so concerned about borrowed names. What I see more of in the Babylonian stories is the clear emergence of a priestly cast and true religion with order and rules.
Looking it at from a structure stand point, I’d say the oldest parts are most likely Genesis and 1 and 2 Samuel and 1 & 2 Kings. You’ll notice numerous violations of Levitical law in Samuel, which barely appears elsewhere. Indicating that the Levitical law we find in Exodus and Leviticus was most likely codified into a formal system after Samuel was written. It looks to me like 1 & 2 Kings were also written in the original Israeli kingdom. The vast majority of Genesis appears to be older as well. There are just a few sections “harmonized” into order with Levitical prescripts.
What most people miss in analyzing Biblical text is the approach the Levities took to updating the books. They never removed anything. So they were forced to add in things side-by-side with the original. Hence why we have Noah collecting 2 of every animal, and then the exact same telling but now it’s 2 of unclean and 7 clean.
Same thing with the creation story. The original version in Chapter 1 just very briefly describes the creation and says that God made man in His image and placed them in dominion over the land and animals.
The Leivitcal version added a lot of specific religious and geographic anchoring to most events. It’s also written in a wildly different style. Chapter 1 is very simple and written in extremely basic language. The 2nd chapter is written by a very scholarly person. Chapter 1 is what you’d get if you asked Trump about Creation, and Chapter 2 is what you’d get if you asked Obama.
Look at the difference
“So God created the great creatures of the sea and every living thing with which the water teems and that moves about in it, according to their kinds, and every winged bird according to its kind. And God saw that it was good."
"A river watering the garden flowed from Eden; from there it was separated into four headwaters. 11 The name of the first is the Pishon; it winds through the entire land of Havilah, where there is gold. (The gold of that land is good; aromatic resin[d] and onyx are also there.) "
Most of Genesis is closer to Chapter 1 than Chapter 2. Abraham, Noah, Jacob, most of these figures are ancient tellings. They may occasionally have a few “harmonizing” verses added in, but the core tellings are ancient. Probably pre-dating writing. The Garden of Eden(including the Fall) and Cain and Abel were probably Levitical editions in Babylon. But other parts bear no such markings.