Amino acid dating accuracy
The Oxford dates were all between 4,500 and 8,500 years BP and the Arizona dates were between 3,000 and 6,600 years BP.Bada et al., (1984) stated that the Oxford AMS results reveal no clear relationship between the radiocarbon ages of the various skeletons and the extent of the aspartic acid racemization.
Then, in the 1980s, something very interesting happened."Stafford et al., (1991) discussed AMS radiocarbon dating in bone at the molecular level.They dated a number of fractions (ranging from insoluble collagen to individual amino acids) from each of a selection of differentially preserved mammoth and human bone.228) argue that the dates only appear to be consistent with one another because of the unacceptably large error range associated with the AAR dates.Pollard and Heron also point out that there is poor concordance between the conventional and the AMS radiocarbon dates and there is no concordance between the uranium series dates and any of the other dates either.Thus the final irony is that the poorly preserved Californian Paleo-Indian bones would return Holocene 14C dates even if they were actually Pleistocene.
The state of preservation of the bone appears to be as important an issue for radiocarbon dating as it is for AAR dating."So, what do we have?
Conventional plus accelerator mass spectrometry (AMS) radiocarbon dating (Taylor et al.
1983) was carried out on the Sunnyvale skeleton and results of between 3,600 and 4,850 years BP were obtained.
The authors of this particular paper went on to suggest that, "As conformation strongly influences the rate of Asu [cyclic succinimide] formation and hence Asx [aspartic acid asparagine] racemization, the use of extrapolation from high temperatures to estimate racemization kinetics of Asx in proteins below their denaturation temperature is called into question . In the position carboxyl to asparagine in the peptide the replacement of glycine with a bulky amino acid such as proline or leucine resulted in a 33-50-fold decrease in the rate of deamidation"Hydrolysis, or the process of breaking down a protein into smaller and smaller fragments, clearly affects the rate of racemization.
The rate itself of hydrolysis "depends on the strength of the individual peptide bonds, which in turn is determined by the characteristics of the amino acids on either side of the bond, the presence of water and the temperature."All of these are confounding factors, which, if not known exactly over extended periods of time, would play havoc with any sort of age determinations.
They all fell within the Holocene but had much larger error estimates than those of the AMS values.