Chapter 5After God has condemned the Watchers to be bound in the depths of the Earth to await the future day of judgement and incited the Nephilim to rise up against and slay each other, and told Noah to build an Ark as all the rest of humanity is to be destroyed, the narrative continues:
He destroyed all [the Nephilim] from their places, and there was not left one of them whom He judged not according to all their wickedness. And He made for all his works a new and righteous nature, so that they should not sin in their whole nature for ever, but should be all righteous each in his kind alway.
The editor of my copy of the Books of Enoch says that Jubilees is unique in saying that God changed human nature in order to cause humankind not to sin any more; no other ancient book says this.There's an odd line in Chapter 7 about the destruction of the Nephilim:
[The Watchers] begat sons the Nephilim, and they were all unlike, and they devoured one another: and the Giants slew the Naphil, and the Naphil slew the Eljo, and the Eljo mankind, and one man another.The Giants are elsewhere identified with the Nephilim (and indeed the my copy of Jubilees translates it here "Nephilim"), but there's no indication here of who the Eljo were. Maybe another type of the Watchers' children, though the line rendered here "they were all unlike" is in my copy of Jubilees translated "they all fought among themselves."
Incidentally, 1 Enoch 7:1-6 describes the Watchers as teaching humans "sorceries and charms, the cutting of roots and the uses of plants." I presume "the cutting of roots" refers to cross-grafting, which the Torah (which has an aversion to the mixing of things of different kinds) explicitly forbids, but it's suggestive to me of the later midrash of the four rabbis who went into the Orchard; one died, one went mad, one cut the shoots, and only one survived with all his faculties intact.
It's commonly thought that Noah's Ark came to rest on Mt Araraṭ, but what the Bible actually says is "on the mountains of Araraṭ". Araraṭ (Urartu in Akkadian) in ancient times was the name of a country, not a single mountain. The Book of Jubilees recognises this, telling us:
The ark went and rested on the top of Lubar, one of the mountains of Ararat.
I have no idea whether Lubar was a known location at the time Jubilees was written. There may be a clue later on, in Chapter 7, where it says:
Ḥām built for himself a city and called its name after the name of his wife Ne'elatama'uk. Jāpheth saw it, and became envious of his brother, and he too built for himself a city, and he called its name after the name of his wife 'Adataneses. And Shem dwelt with his father Noah, and he built a city close to his father on the mountain, and he too called its name after the name of his wife Sedeqetelebab. And behold these three cities are near Mount Lubar; Sedeqetelebab fronting the mountain on its east; and Na'eltama'uk on the south; 'Adatan'eses towards the west.