Complex sentence: The earliest form of the book stems from an ancient Jewish Aramaic tradition regarding the Nephilim (the gigantic offspring of the sons of god and the daughters of men) found in Genesis 6:1-4 and expanded in 1 Enoch.
Split into simpler sentences: The earliest form of the book stems from an ancient Jewish Aramaic tradition regarding the Nephilim. However, references are found in Genesis 6:1-4 and expanded upon in 1 Enoch.