The carbon-14 method is slightly different from other dating methods. Normal carbon has an atomic weight of 12. Carbon-14 is the unstable form produced by cosmic ray bombardment of nitrogen in the earth’s upper atmosphere. The C-14 combines with oxygen to form carbon dioxide, which then takes its place in the great carbon cycle. That is, the carbon dioxide becomes the food for plants and trees, and these in turn become food for animals and humans. The net result is that every living thing contains normal carbon (C-12) and some C-14.
When a living organism dies, it no longer takes in carbon, and the C-14 it contains at the time of death continues to decay and revert to normal nitrogen. The longer a once-living thing has been dead – whether it is wood or bone – the less C-14 it contains. Carbon-14 decays relatively quickly, and at about 50,000 years after the death of the organism no C-14 atoms will be left in the remains. This, then, is the time limit for the method. As in the case of the other radiometric methods, the technique consists of measuring the ratio of C-14 to C-12 in the specimen and calculating the age based on the known rate of decay.
Civilization extends back about 5,000 years, so it is possible to calibrate the C-14 method against historically dated materials. In fact, wood from dated coffins was used in the early work that established this method. However, the method is really only reliable within the limits of calibration, and even then there are some problems. It is well known, for example, that materials older than about 3,000 years begin to yield much older ages. Conversely, those who believe in the old ages have always complained that the C-14 method gives ages that are too young. “Fudge factors” have to be employed to bring the reported ages within the limits of the expected dates! This is hardly good science!
One of the principle problems of the method lies in the assumption that C-14 has been produced in the upper atmosphere for millions of years and that it long ago reached a steady state. In other words, the amount of C-14 now being generated is exactly equal to that being lost by decay. However, measurements show that C-14 is still rapidly building up in the atmosphere. This fact alone indicates that the atmosphere is only a few thousand years old. This also has the effect of making C-14 ages appear to be older, especially the earlier dates.
The C-14 method began with great promise in 1948. But over the years it has proven to have more and more problems until today many scientists consider the method to be discredited. Spurious results are well known, such as living specimens dating out at thousands of years. This suggests the possibility that some living organisms have the ability to quickly reject C-14 atoms from their bodies. If this is the case for the animal kingdom, it would seemingly limit the method to the plant kingdom – namely wood.
Finally, when the method was first introduced, age determinations were enthusiastically made on coal, oil, and nonmineralized dinosaur and human bones. The ages were reported in Radiocarbon Journal and in each case were less than 10,000 years.