This is from Alamo-Girl's essay at the start of this thread:
The oldest known Jewish work not included in the Bible is the Book of Enoch. This is a complex work, written in the third (or perhaps even the late fourth) century BCE, after the return from the Babylonian Exile and the establishment of the Second Jewish Commonwealth (6th-5th centuries BCE) and before the Maccabean revolt in 172 BCE. The oldest copies of the Book of Enoch, dating from the third century BCE, were discovered among the Dead Sea Scrolls (see below).