Discussion on this thread has traveled far and wide with YEC proponents trying a number of arguments. I'll touch on three of them:
the age of the earth, reliability of dating methods etc: problem is that the earth is old, according to the objective empirical evidence the earth is over 4.5 billion years old. Further discussion of this fact can be taken to Age Correlations and An Old Earth, Version 2 No 1.
fossils of marine animals show flooding: what the fossils show is that the land at the time of the fossils was underwater, not that water covered the whole world, and the fossils found show evidence of decades if not centuries of generation after generation of marine life in that particular spot, whether flat land or the top of Mt Everest -- a duration of life that is completely incompatible with the purported flood. Further discussion of this fact can be taken to Trilobites, Mountains and Marine Deposits - Evidence of a flood? (if reopened) or a new thread on this topic.
but the genetic bottleneck argument presented by Jar is, imho, the most devastating to the concept that a world wide flood occurred and that as a result all living species descend from a handful of individuals -- a genetic bottleneck that should show up in every single species on earth. This is truly objective empirical evidence that there was no such event.
The choice is simple:
the objective empirical evidence shows the earth is extremely old and that there was no species wide bottleneck event, and thus believing in a young earth and a global thread can only be sustained by the other choice,
all evidence is illusion, fabricated by a joker god that wants to delude you, either with stories or with facts.