“This pseudepigraph has evoked divergent opinions; but today there is a consensus that the book is a composite, portions of which are clearly pre-Christian as demonstrated by the discovery of Aramaic and Hebrew fragments from four of the five sections of the book among the Dead Sea Scrolls. One of these fragments, moreover, Hena, was copied in the second half of the second century B.C.
The main question concerns the date of the second section, chapters 37-71, which contains the Son of Man sayings. J. T. Milik (esp. no. 755) has shown that this section, which is not represented among the early fragments, is probably a later addition to 1 Enoch; but his contention that it was composed around A.D. 270 (no. 755, p. 377) is very speculative. If, as most specialists concur, the early portions of 1 Enoch date from the first half of the second century B.C., chapters 37-71 could have been added in the first century B.C. or first century A.D.
The original language of 1 Enoch appears to be Aramaic, except for the Noah traditions, which were probably composed in Hebrew. The earliest portions display impressive parallels with the nascent thoughts of the Jewish sect which eventually settled at Qumran.”
Related: James H. Charlesworth. wikipedia.org