Amino Acid Racemization

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Amino acid racemization dating is a technique that is used to date fossilized objects up to several millions of years in age. The naturally occurring amino acid molecules usually possess a carbon centre with four different groups joining it; a hydrogen atom, the amino group, the acid group (hence the name of the class of molecule) and a side chain, which is what distinguishes amino acids.

In three dimensional space, such a molecular topology can occupy one of two configurations; D (right), or L (left), which are referred to as stereoisomers and are essentially mirror images of each other. The ratio of these two isomers is initially unequal (with only one exception, naturally occurring amino acids used in polypeptide synthesis are in the L form) but over time this will decay to a more balanced state in a process called racemization, where the ratio between L and D stereoisomers will be equal.

Measuring the degree of racemization and other known quantities can give you an estimated age of the sample. By measuring the racemization of the amino acid isoleucine, for example, objects can be dated up to several million years old1. While it is true that there can be great variability on the rate at which amino acids undergo racemization, the changes in humidity, temperature, and acidity required to make the oldest known samples conform to a young earth (under 6000 years) view are completely unreasonable.(2)

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