Amino acid racemization dating method
The original amino acid extractions from the racemization studies of the Paleo-Indian remains were independently dated by the AMS radiocarbon method at the Oxford Radiocarbon Accelerator Unit of Oxford University and the NSF Accelerator Facility for Radioisotope Analysis, University of Arizona.Bada et al., (1984) published the Oxford results and Taylor et al., (1985) published a paper combining the results from both laboratories.
For example, even today "very little is known about the protein structure in ratite eggshell and differences in primary sequence can alter the rate of Asu formation by two orders of magnitude [100-fold] (Collins, Waite, and van Duin 1999).In turn, proteins are composed of folded strands of 20 different smaller subunits called "amino acids".All amino acids, except for one (glycine), come in two different forms known as the levoratory (L - left) and dextrorotary (D - right) forms.Then one could use this as an independent test on other dating schemes.I heard of a case where ancient fossils were dated this way and turned out to be tens of thousands of years old, rather than millions of years old.In this light, it is interesting to consider what happened in 1974 when some of the major proponents of amino acid dating (Bada et al) decided to analyze the Paleo-Indian skeletal material from Del Mar, California.
Their estimated age of 48,000 years before present (BP) "stunned" the archaeological community who generally believed these bones to be less than 10,000 years old.
Of course, since this technique may be calibrated in terms of Carbon 14 dating, which itself may be open to question, even those dates may be wrong.
Anyway, I'd be interested to know, if one extrapolates known (laboratory measured) rates of racemization back in time, what kind of a check does this give on Carbon 14 and other dating methods.
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.
An article in the Dec 13, 1996 issue of Science, page 1842, discusses dating based on the amino acid racemization technique. ) form, but with time some transform to the D (right) form.