there are many discrepancies, too many on erev shabbos to handle. suffice it to say that Torah was the blueprint of creation. It was written thousands of years before creation and the creation was modeled to it. in order to understand this concept you must be aquainted with chassidus. The physical actions and understandings of people are merely reflections of the truth as shown by HaShem to his people and come down to us from a higher spiritual source. the world is a reflection of those concepts. Avraham knew, or discovered those concepts and therefore understood not only the values but also the ritual. Avraham sacrifices in a "Jewish" fashion for instance and serves matza during the time of year which would be Pesach, etc. Ask a ChaBad Rabbi to fill you in if you need to know more. We know that Shem and Eber lived quite awhile after the flood and passed down much of this knowledge to those who wanted to learn it. This idea, of course is ancient Jewish legend and you are free to disagree if you choose, (non-Jews) and challenge it. however, the stories are there and passed down (like the oral law was) for thousands of years. of course when people want to believe certain things and discount others to prove their own point, they will do so. the consistency of the Jewish story is it's own best evidence.
another place to start is here with an essay based upon the teachings of the Lubavitcher Rebbe, OBM.