The thing is, everybody can TEST the archeological evidence themselves. You can do all the nuclear physics calculations and you can do the measurements and there is plenty of evidence of places ALL over the world. Cave paintings in Europe, the early (advanced) settlements that date back to 12,000BC.
Decay of carbon matter (such as wood and plant material to build the earliest houses as well as the people that lived there), halflife of several different radio-isotopes, geological layers (depth) and contemporary fossils in the vicinity, those are all different methods that can give a date-time period (some more precise than others). If there were major problems in one or all of these (scientific) theories (learn what a theory IS before answering), then they will give wildly different times. The problem for creationists is that they don't give a different time.
Even so, if the flood were true, you would have a mass-extinction event. We have had mass-extinction events in earth's history repeatedly (that's how most of the dinosaurs disappeared and why we only have relatively small dinosaurs (eg. crocodiles and cephalopods) left) but the most recent one is ~50M years ago, not 6,000 years.