14 radiocarbon dating
There is, in fact, no indication anywhere in the original reference that these samples were from the "Pennyslvanian"; nor is there any hint that they were expected to be "300 million years old"; these appear to be purely apocryphal embellishments to the original account.Surely, what the Russians intended to convey (and what nearly everybody would understand), is that these samples were charcoal from a not too ancient campfire.
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.
If this water is in contact with significant quantities of limestone, it will contain many carbon atoms from dissolved limestone.
This is evident first of all by the fact that it is part of a date list which is broken into three parts: "geologic samples", "archaeological samples", and "fossil animals".
Clearly, Pennsylvanian coal would be listed as a geologic sample, but this sample of "coal" is listed as an archaeological sample. In the original reference the sample is described as "scattered coals in a loamy rock in deposits of a 26-m [river] terrace".
This Radiocarbon reference must originally have been translated from Russian and it is not unreasonable to suppose that there was some loss of descriptive clarity as a result.But it seems pretty clear that what is being described here is certainly not "Pennsylvanian coal".A number of stories are commonly circulated about a shell, or a piece of coal, or some other sample which supposedly yielded a radiocarbon date which could not possibly be correct.Such stories misrepresent the truth and do a disservice to science and public knowlege.Presented here are a few examples, exposing the truth about these stories.A brief look at the original reference [Vinogradov et al., page 319.]...immediately reveals that the sample was not Pennsylvanian coal at all.