I've read that book. I'm just not sure about the further idea of angels marrying women and having children by them (Genesis 6).
Discussion
I first heard that theory many decades ago, and discounted it heavily...
However, I've given it much more credence lately, partly from reading Heiser, partly reading Enoch, partly listening to Expedition 44, partly from observing and struggling with nation-states myself, as well as contemplating my own readings in the Koine Greek New Testament.
it's extensively discussed in Enoch, and in genesis it's practically the main reason given for why the world needed to be washed away... though considering the science of pole shifts and the geomagnetic disaster cycle that was probably just what was interpreted from it in the time in between, since as far as we know there isn't actually texts older than this
except it does say in enoch that reading and writing were not widely known among his people, and he learned it from the angels, and spent quite some time teaching this knowledge not just to his family, at one point, yes, if you read some other genesis apocrypha, like Jasher, especially (which also strongly hints at the idea that adam and eve were in eden to learn to farm, it even specifies they had a 7 year course), which all lines up with the idea that the whole thing is something of a cargo cult, but at the same time... if there was a civilization that advanced that much past their peers it would be like the opposite of the famous cargo cults of WW2, as in, imagine if this modern tech society was keeping to itself instead of going around conquering and shit... then you sorta see, it was another sign that they were more advanced because they held noninterference very highly as a principle and as such while they visited other lands they mostly were just showing up to give warnings or help out in some situation they heard about
I'm suspicious of the book of Enoch, though. Off the top of my head, I think the earliest attestation of it is from the second century BC. That's a few millennia after the real Enoch lived, which means the so-called book of Enoch was not really written by him. It should be called Pseudo-Enoch. And the same could be said for the book of Jasher.
all of the old testament was oral tradition for a long time before being written down, that's not an argument against anything old
and it's arguable that just because Thomas leans towards gnosticism doesn't mean it doesn't belong in the New
after having read genesis in several versions all the way through i'm of the opinion that the timeline is not correct, and that actually Noah was around about 13000 years ago, and that there is many holes in the story because there literally isn't anything more than about 3000 years old that has been found related to the texts of the catholic canonical bible selection
also, once you've read Enoch you understand that in the time of Jesus this was a widely studied text and many of his most famous sayings are actually from Enoch
the angels liked him so much they let him go and live with them
very likely the many threads that trace back from most of the good things recorded in text in the last 5000 years came from his teaching work, and not just in europe and middle east but the whole world, according to Jasher
I find Harold Camping's biblical chronology the most thoroughly researched and credible.
https://may-212011.com/downloads/TimeHasAnEnd.pdf
I know many dismiss Camping because of his failed predictions of the end of the age, but I believe he was an honest scholar who truly strove to uncover and live by the truth of scripture.
the thing is this:
the stuff about the lifespan reducing to 120 years happens around the time of Abraham, and yet supposedly only a few generations before that, the ages were in the 900r1200 year range, and right in the middle of that same part of the story, we have what are clearly stories of meteor impacts destroying several large cities
first of all, does it seem likely that a man who lived this long suddenly his children lost their lifespan?
second, what are the possible causes for swarms of large meteors hitting the earth? there is the taurid swarm, that one is discussed in Yajnavalkya, but there is also another that the book doesn't account for that is now starting to be well known - micronovas and superflares from the sun throw up enormous amounts of material that cool and coalesce into large rocks and it is known that there is a pattern of large meteor impacts and geomagnetic shifts that make sense to have been related to a large solar eruption due to how close together they happen
so i think that Adam was about 15000 years ago like Yajnavalkya says, and then 6 generations later we have Enoch and then another two and Noah and then the flood, and then there was a cooling period and then about 5000 years until the time of Abraham and then the oldest surviving texts known are around 5000 years back from now and we are coming up to a new solar mega-flaring period that will bring again, just like said in so many books including Revelation, another great conflagration and again John repeats a lot of what was told in Enoch and Daniel - Enoch particularly the "Head of Days" talks about how things didn't quite go according to plan in Noah's story and that when the circle comes around again - which would be 12000 years because that's the time between the massive global events like the Flood, they would make double sure that they didn't let any of the descendants and followers of Satan survive this next one.