Radiometric dating uncertainty
Thus, the older a fossil shell or bone, the greater should be the extent of racemization of the amino acids which are contained in the proteins found in the bone or shell.
Hare and Mitterer measured the rate of racemization of L-isoleucine to D-alloisoleucine in modern shell fragments heated in water at high temperatures and extrapolated these data to lower temperatures in order to estimate the rate of racemization of L-isoleucine in fossil shells to obtain what they believed to be an approximate age for these fossil shells.
In other work, the rate of racemization of aspartic acid, instead of isoleucine, was used.
The rate of racemization is highly temperature dependent.
All of the amino acids which occur in proteins, except for glycine, which is the simplest amino acid, have at least one asymmetric carbon atom, and can exist as one of two possible stereoisomers.
That is, the chemical groups attached to this particular carbon atom are all different and can be arranged in space in two different ways.
From a combination of conclusions based on these rates, the actual extent of racemization of isoleucine in fossil bones, and the estimated average temperatures at which these fossil bones are believed to have existed, ages were calculated.Amino acids are the "building blocks," or sub-units, of proteins.About 20 different kinds of amino acids are found in proteins.The racemization of L-isoleucine to D-alloisoleucine is, therefore, of special interest in the amino acid racemization dating system.Since the amino acids in proteins of living things are of the L-form, but upon death of the plant or animal spontaneously tend to change to mixtures of the L- and D-forms, the extent of this racemization process could possibly serve as a dating method.