Amino acid dating - Wikipedia
PDF | The development of amino acid racemization as a dating technique holds considerable promise for resolving questions of human. term survival of endogenous amino acids. Analysis AAR dating of mammalian collagen-based biominerals (e.g. bone and dentine) has had. Definition. A method for estimating the relative age since death by assessing the Amino acid racemization (AAR) dating is a geochronological technique with a.
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. It is, perhaps, best considered to be a calibrated relative dating technique which puts it somewhere between relative and chronometric methods.
Amino acid racemisation
In fact, the difficulties are so great that this technique cannot be and is not used as any sort of "absolute" dating technique. So, how is it thought to be at all helpful? Well, it is thought to be helpful as a "relative" dating technique. To overcome the various uncertainties inherent to amino acid dating, the method must be "calibrated" based on other more reliable techniques such as radiocarbon dating carbon 14 dating.
These values are used to solve for a constant or "k" in the formula used to estimate ages based on the calibration sample. Of course, the "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.
At first "cubic transformations"' and then later "power function transformations" were used that seemed to show a "strong correlation with time, but did not explain the observed kinetics. So, if there is any problem with the basis of the correlation i.
In this light, it is interesting to consider what happened in 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, years before present BP "stunned" the archaeological community who generally believed these bones to be less than 10, years old. Bada went on to date other skeletal specimens between the 35, and 48, year range with one specimen from Sunnyvale being dated at an astonishing 70, years BP. Then, in the s, something very interesting happened. Conventional plus accelerator mass spectrometry AMS radiocarbon dating Taylor et al. The Oxford dates were all between 4, and 8, years BP and the Arizona dates were between 3, and 6, years BP.
They did note that there appeared to be a direct relationship between the extent of racemization and the level of preservation of collagen in the bones. Those samples with the most racemization had the lowest amino acid content and this poor preservation of protein would contribute to anomalous AAR results.
Later, based on AMS radiocarbon dates, Bada calculated a new value for kasp for the Californian samples. He used the Laguna skull and the Los Angeles Man skeleton as 'calibration' samples for this. They all fell within the Holocene but had much larger error estimates than those of the AMS values.
Amino acid dating
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. At best three of the four methods put the bones in the Holocene. That is because the porosity of bones makes them more "open" to surrounding environmental influences and leaching. Specimens that are more "closed" to such problems are thought to include mollusk shells and especially ratite bird eggshells from the emu and ostrich.
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 [fold] Collins, Waite, and van Duin Goodfriend and Hare show that Asx racemization in ostrich eggshell heated at 80 oC has complex kinetics, similar to that seen in land snails Goodfriend The extrapolation of high temperature rates to low temperatures is known to be problematic Collins, Waite, and van Duin Temperature and humidity histories of microenvironments are being produced at ever increasing rates as technologies advance and technologists accumulate data.
These are important for amino acid dating because racemization occurs much faster in warm, wet conditions compared to cold, dry conditions.
Amino Acid Dating. Is it reliable?
Temperate to cold region studies are much more common than tropical studies, and the steady cold of the ocean floor or the dry interior of bones and shells have contributed most to the accumulation of racemization dating data.
Generally, they are not assumed to have a great impact in the natural environment, though tephrochronological data may shed new light on this variable. The enclosing matrix is probably the most difficult variable in amino acid dating. This includes racemization rate variation among species and organs, and is affected by the depth of decomposition, porosity, and catalytic effects of local metals and minerals.
This amino acid ratio has the advantages of being relatively easy to measure and being chronologically useful through the Quaternary. Archeology stratigraphyoceanographypaleogeographypaleobiologyand paleoclimatology have been particularly affected. Their applications include dating correlation, relative dating, sedimentation rate analysis, sediment transport studies,  conservation paleobiology,  taphonomy and time-averaging,    sea level determinations, and thermal history reconstructions.
Bone, shell, and sediment studies have contributed much to the paleontological record, including that relating to hominoids. Verification of radiocarbon and other dating techniques by amino acid racemization and vice versa has occurred.
How does amino acid dating work
Paleopathology and dietary selection, paleozoogeography and indigineity, taxonomy and taphonomyand DNA viability studies abound. The differentiation of cooked from uncooked bone, shell, and residue is sometimes possible. Human cultural changes and their effects on local ecologies have been assessed using this technique.