Regardless of whether the original source exist from "Adam to Abraham", you do realise that the Qur'an is not considered to be the original source?
And beside this, the Bible (Hebrew or Christian) WAS NOT JUST ONE BOOK, but whole collection of works.
The Qur'an was not even written down in Muhammad's lifetime. Supposedly, Muhammad's disciples have written down pieces of the so-called Qur'an or handed down orally (oral traditions), but it was not until the the third Caliph, Uthman, had people compiled to all these pieces together.
And considering there is a long of history of the development, and the presences of Christians and Jews in the Arabian peninsula, before and during Muhammad's time, the Judaeo-Christian stories were known to the Arabs.
As much as you like to rant on about the Qur'an being a divine revelation from Allah, it is hardly what I call "believable" historical event. Gabriel telling Muhammad the "Qur'an" is no more believable than Joseph Smith Jr, receiving gold tablets and translating it into the Book of Mormon. It is fairytale, and only as gullible as you could swallow this whole. How Muhammad receive the Qur'an is no more believable than the Qur'an version officer Solomon's ability, being able to control the winds, and command army of ants, birds and jinns; fable. You might as well as accept the Gabriel visiting Muhammad as any one of those tales from the Arabian Nights.
Like Caladan said, there are historical evidences of the development of Judaic and Christian writings. And the writings were not all written down at the same times.
I don't think you have any understand the long process, or if you do, you simply scoff it off. But historical development of these scriptural literature are more likely to be true, then the ridiculous claim of Gabriel meeting Muhammad, Gabriel passing down the Qur'an, Muhammad not being able to write, Muhammad didn't know the biblical stories. All baseless as the Qur'an being the original source of all scriptures.