Of course, even if these rather thin specimens were actually "closed" systems (more so than even teeth enamel) they would still be quite subject to local temperature variations as well as the other above-mentioned potential problems.
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).
As a matter of fact, the ages obtained from racemization dating must rely on other techniques such as Carbon 14, and if the dating of Carbon 14 is not accurate, racemization dating can never be certain."major assumption required with this approach is that the average temperature experienced by the 'calibration' sample is representative of the average temperature experienced by other samples from the deposit."What this basically means is that amino acid dating is not based on any sort of understanding about how racemization takes place, but is strictly a function of correlation with other dating techniques, such as the radiocarbon technique.
This seems especially likely when one considers that each type of specimen and each different location have different k-values meaning that the radiocarbon-derived constant in one region or with one type of specimen cannot be used to calculate the age of any other specimen or even the same type of specimen in a different location.
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.
These two forms are called "enantiomers", "chirals", or "stereoisomers", which basically means that they have the same molecular and structural formula but cannot be superimposed on each other no matter how they are oriented in space.
Such extrapolations have been fairly recently (1999) called into question by experiments showing that models based on high temperature kinetics fail to predict racemization kinetics at physiologic temperatures (i.e., 37 C). We argue that the D: L ratio of Asx reflects the proportion of non-helical to helical collagen "The local buffering effects of bone and shell matrixes are supposed to limit this effect, but it is still something to consider as potentially significant when acting over the course of tens of thousands to millions of years.replacement of the asparagine residue with aspartic acid resulted in a 34-fold decrease in the rate of succinimide (Asu) formation.
Even the process of preparing a specimen for racemic dating can affect the D/L ratio.