If the flood happened, the dating data recorded would be off due to unknown pre-flood consistency of the atmosphere elements and that in organisms.
How could a flood alter elemental isotopes? I know you've long asserted this as a result of a putative Biblical Flood - that somehow the Pre-Flood Earth had different ratios of various elemental isotopes than the Post-Flood Earth - but I've never seen you explain exactly how plain water is supposed to do that. This seems like something you assume the Flood can do because you have to assume it, because you have to have a Pre-Flood Earth with different isotope ratios in order to queer the radiometric dating, which always has been the strongest evidence against a short history for life on Earth.
In order to change the ratio of isotopes of a material, at least one of the following has to happen:
1) Sufficient time has to proceed to allow radioactive decay to eliminate the more unstable isotopes. 2) Nuclear reactions have to occur that result in fission or fusion of nuclei.
It's possible, mechanically, to separate isotopes by weight, but that doesn't really alter isotope ratios, it just moves them around in space.
Please note - plain water can't cause nuclear reactions. It's all very well and good for you to imply that the Great Flood somehow changed the isotope ratio of the entire Earth, but what could possibly be the explanation for how water was able to do that?