To derive ages from such measurements, unprovable assumptions have to be made such as: There is plenty of evidence that the radioisotope dating systems are not the infallible techniques many think, and that they are not measuring millions of years. For example, deeper rocks often tend to give older “ages.” Creationists agree that the deeper rocks are generally older, but not by millions of years.
Geologist John Woodmorappe, in his devastating critique of radioactive dating, points out that there are other large-scale trends in the rocks that have nothing to do with radioactive decay.
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.
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.
So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.
The amount of cosmic rays reaching the Earth varies with the sun's activity, and with the Earth's passage through magnetic clouds as the solar system travels around the Milky Way galaxy.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.This is the “half-life.” So, in two half-lives, or 11,460 years, only one-quarter of that in living organisms at present, then it has a theoretical age of 11,460 years.Anything over about 50,000 years old, should theoretically have no detectable C.That is, they take up less than would be expected and so they test older than they really are.Furthermore, different types of plants discriminate differently.Also, the Genesis flood would have greatly upset the carbon balance.The flood buried a huge amount of carbon, which became coal, oil, etc., lowering the total C ratio in plants/animals/the atmosphere before the flood had to be lower than what it is now.The strength of the Earth's magnetic field affects the amount of cosmic rays entering the atmosphere.A stronger magnetic field deflects more cosmic rays away from the Earth.