Amino acid dating accuracy

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.

Even the process of preparing a specimen for racemic dating can affect the D/L ratio.

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Due to the strong dependency of racemization rates on temperature, water concentration, and alkalinity, uncertainties regarding conditions of preservation can leave amino-acid-based age relationships among even similar fossils open to question.

At the present time there is insufficient knowledge concerning the effective average racemization rate in a fossil as a function of time to justify dependence on D/L ratios for a quantitative determination of age.

Racemisation it is a post-mortem spontaneous reaction, involving the interconversion between two different forms of a single amino acid, the D- and L-forms (these are chemically identical but differ in the spatial configuration of their atoms).

L-amino acids are present in living organisms, while D-amino acids are formed post-mortem by racemisation.

isomer which is initially absent in skeletal material.

In turn, proteins are composed of folded strands of 20 different smaller subunits called "amino acids".The survival of amino acids in fossils from the Paleozoic era and the trend for the apparent racemization rate constant to decrease with conventional fossil age assignment raise a serious question concerning the accuracy with which radioisotope age data have been used to represent the real-time history of fossils.The instability of the twenty amino acids which are the building blocks of proteins provides a possible means for determining the ages of fossils.The extent of racemisation can be measured by the ratio between the concentrations of D- and L-forms detected in a fossil sample: this is called D/L value. The D/L value yields an estimate of the time elapsed since the death of the organism: older fossils will have higher D/L values (closer to 1) (see Fig. However, for the use of amino acid racemisation (AAR) as a reliable dating tool, analysis of proteins from a closed system within fossils is vital. Dating Pleistocene archaeological sites by protein diagenesis in ostrich eggshell. The amino group of one amino acid can combine with the carboxyl group of a second amino acid to form a "peptide" bond, and its carboxyl group can combine with the amino group of a third amino acid, and the chain can thus be extended indefinitely.

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