Radio carbon dating coal
Other radiometric dating methods such as potassium-argon or rubidium-strontium are used for such purposes by those who believe that the earth is billions of years old.
Radiocarbon is not suitable for this purpose because it is only applicable: a) on a time scale of thousands of years and b) to remains of once-living organisms (with minor exceptions, from which rocks are excluded).
First, any instrument which is built to measure radiocarbon has a limit beyond which it cannot separate the signal due to radiocarbon in the sample from the signal due to background processes within the measuring apparatus.
Even a hypothetical sample containing absolutely no radiocarbon will register counts in a radiocarbon counter because of background signals within the counter.
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.
They have been slowly built up by matching ring patterns between trees of different ages, both living and dead, from a given locality.
The shells of live freshwater clams can, and often do, give anomalous radiocarbon results.
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.
Measurements made using specially designed, more elaborate apparatus and more astute sampling-handling techniques have yielded radiocarbon ages for anthracite greater than 70,000 radiocarbon years, the sensitivity limit of this equipment. Continuous series of tree-ring dated wood samples have been obtained for roughly the past 10,000 years which give the approximate correct radiocarbon age, demonstrating the general validity of the conventional radiocarbon dating technique.
Several long tree-ring chronologies have been constructed specifically for use in calibrating the radiocarbon time scale.These two measures of time will only be the same if all of the assumptions which go into the conventional radiocarbon dating technique are valid.