These techniques are applied to igneous rocks, and are normally seen as giving the time since solidification.The isotope concentrations can be measured very accurately, but isotope concentrations are not dates.
Since the flood was accompanied by much volcanism (see Noah's Flood…, How did animals get from the Ark to isolated places? ), fossils formed in the early post-flood period would give radiocarbon ages older than they really are.In summary, the carbon-14 method, when corrected for the effects of the flood, can give useful results, but needs to be applied carefully.These techniques, unlike carbon dating, mostly use the relative concentrations of parent and daughter products in radioactive decay chains.For example, potassium-40 decays to argon-40; uranium-238 decays to lead-206 via other elements like radium; uranium-235 decays to lead-207; rubidium-87 decays to strontium-87; etc.Overall, the energy of the Earth's magnetic field has been decreasing, so more C is being produced now than in the past.
This will make old things look older than they really are.
It does not give dates of millions of years and when corrected properly fits well with the biblical flood.
There are various other radiometric dating methods used today to give ages of millions or billions of years for rocks.
This also has to be corrected for. Second, the ratio of C in the atmosphere at that time to be estimated, and so partial calibration of the “clock” is possible.
Accordingly, carbon dating carefully applied to items from historical times can be useful.
However, even with such historical calibration, archaeologists do not regard C produced and therefore dating the system.