Carbon radioisotope dating
However, in either case, the background beta radiation has to be compensated for, and, in the older objects, the amount of C-14 they have left is less than the margin of error in measuring background radiation. Question: Creationists such as Cook (1966) claim that cosmic radiation is now forming C-14 in the atmosphere about one and one-third times faster than it is decaying.As Hurley points out: Without rather special developmental work, it is not generally practicable to measure ages in excess of about twenty thousand years, because the radioactivity of the carbon becomes so slight that it is difficult to get an accurate measurement above background radiation. 108) Cosmic rays form beta radiation all the time; this is the radiation that turns N-14 to C-14 in the first place. If we extrapolate backwards in time with the proper equations, we find that the earlier the historical period, the less C-14 the atmosphere had.Since the tree ring counts have reliably dated some specimens of wood all the way back to 6200 BC, one can check out the C-14 dates against the tree-ring-count dates.Admittedly, this old wood comes from trees that have been dead for hundreds of years, but you don't have to have an 8,200-year-old bristlecone pine tree alive today to validly determine that sort of date.Carbon from these sources is very low in C-14 because these sources are so old and have not been mixed with fresh carbon from the air.Thus, a freshly killed mussel has far less C-14 than a freshly killed something else, which is why the C-14 dating method makes freshwater mussels seem older than they really are.The older an organism's remains are, the less beta radiation it emits because its C-14 is steadily dwindling at a predictable rate.
This means that the tree-ring dates would be slightly too young, not too old.If we extrapolate as far back as ten thousand years ago, we find the atmosphere would not have had any C-14 in it at all.