They have their work cut out for them, however, because radiocarbon (C-14) dating is one of the most reliable of all the radiometric dating methods.
Such multiple growth rings are extremely rare in bristlecone pines, however, and they are especially infrequent at the elevation and latitude (37� 20' N) of the sites being studied.
In the growth-ring analyses of approximately one thousand trees in the White Mountains, we have, in fact, found no more than three or four occurrences of even incipient multiple growth layers. 840) In years of severe drought, a bristlecone pine may fail to grow a complete ring all the way around its perimeter; we may find the ring if we bore into the tree from one angle, but not from another.
Hence at least some of the missing rings can be found.
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.
Most of the tree-ring sequence is based on the bristlecone pine.