My knowledge on the early stages of Christianity is limited, as I am still very much a student like you SP. However, is it not likely or possible that 'Mark's' writings could have reached the areas of other scholars of the time, who then could have re-written their own replication (and I use that term very loosely) for their current audience?
Additionally, there is not a shred of physical, concrete evidence that even implies Christ ever existed. The Bible isn't concrete evidence, the Gospels are narrative stories that have little to no factual credibility in them whatsoever. The cruicifixtion actually taking place and the documented 'recount' of it are two completely different things, with one likely to never have even happend.
I won't go too deeply into this, as I'm not here to win Nank's debate. I just wanted to put a few points forward for you to clarify.
UYI