Fossils.
Fossils are almost never dated radiometrically, since they hardly ever contain enough of the radioactive substances required. A common way of dating fossils (and rocks without said radioactive elements) is by 'dating' an associated volcanic rock (often using the K-Ar method). It depends on the rate at which radioactive K (potassium) decays into the gas Ar (argon).
The K-Ar method works like this:
When the volcanic rock hardens the 'clock' begins ticking. That is, it assumes there is no argon that used to be potassium present to begin with, but after the lava cooled and solidified, the argon from radioactive decay couldn't get out (cause it's inside a rock
) and so after x number of years there
should be y amount of argon. (Whoops!)
However, it is well-known that if a radiometric 'date' contradicts a fossil-derived (and evolutionary) age, the date is discarded as erroneous.
Evolution 0, Creationism 2
ps. ChaosWulf: your flood argument works both ways.