The changing ratio of C-12 to C-14 indicates the length of time since the tree stopped absorbing carbon, i.e., the time of its death.
Although I can find any number of references to this seemingly vital finding on the creationist sites, I can find almost no attempt to refute or explain this anomaly on serious science sites. There seem to be some unsubstantiated references to the possibility of neutrons generated by uranium decay resulting in an anomalously high presence of C14.The problem: If the material is too old, the small amount of C14 present may not decay in the measurement interval. Nearby radioactive material could trigger exactly the same C14 production process from nitrogen as occurs in the upper atmosphere, albeit at a much reduced rate.Newer, more accurate techniques use mass spectroscopy. It doesn't take much contamination to spoil a sample with near-zero quantity of C14. Another possible avenue is C13, which has a small but non-zero neutron absorption cross section.It is only useful for once-living things which still contain carbon, like flesh or bone or wood.Rocks and fossils, consisting only of inorganic minerals, cannot be dated by this scheme.I have tried here to answer some of the frequently asked questions that I receive from students via email, as well as providing some basic information about scientific dating methods."Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure.Outside the range of recorded history, calibration of the 14 clock is not possible.This means the above calculations are only evolution speculation and NOT backed up by real science.Carbon normally occurs as Carbon-12, but radioactive Carbon-14 may sometimes be formed in the outer atmosphere as Nitrogen-14 undergoes cosmic ray bombardment.The resulting C-14 is unstable and decays back to N-14 with a measured half-life of approximately 5,730 years.They used pottery and other materials in sites to date 'relatively'.They thought that sites which had the same kinds of pots and tools would be the same age.We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess." [Rasmus Nyerup, (Danish antiquarian), 1802 (in Trigger, 19)].