C 14 dating controversy

For example, a sample with a true radiocarbon age of 100,000 radiocarbon years will yield a measured radiocarbon age of about 20,000 radiocarbon years if the sample is contaminated with a weight of modern carbon of just 5% of the weight of the sample's carbon.

However, the reason for this is understood and the problem is restricted to only a few special cases, of which freshwater clams are the best-known example.It is not correct to state or imply from this evidence that the radiocarbon dating technique is thus shown to be generally invalid.The problem with freshwater clams arises because these organisms derive the carbon atoms which they use to build their shells from the water in their environment.Long tree-ring chronologies are rare (there are only two that I am aware of which are of sufficient length to be of interest to radiocarbon) and difficult to construct.They have been slowly built up by matching ring patterns between trees of different ages, both living and dead, from a given locality.