Amino acid dating

He was quoted as saying that he had discovered the basis of the method in 1968, and that it was so obvious and simple he was amazed it hadn't been discovered earlier.As a matter of fact, the basis of this method had been discovered earlier and had been reported in a series of papers published by Hare, Mitterer and Abelson in 1967, 1968, and 1969.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.

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At a widely publicized news conference in August of 1972, Dr.

Jeffrey Bada of Scripps Institute of Oceanography announced the "discovery" of a new dating method based on the rate of racemization of amino acids in fossil material.

In turn, proteins are composed of folded strands of 20 different smaller subunits called "amino acids".

All amino acids, except for one (glycine), come in two different forms known as the levoratory (L - left) and dextrorotary (D - right) forms.

Investigation of amino acids in fossils over the past thirty years has revealed that residual amino acids may exist in fossils from throughout the Phanerozoic portion of the geologic column, that the amino acid pattern in a given fossil changes with age due to differences in stability among the twenty amino acids of which proteins are constructed, and that the ratio of right-handed to left-handed forms (D/L ratio) of amino acids increases with age from zero in the proteins of living organisms to the ratios which are characteristic of amino acids produced synthetically (the racemic ratios).

The possibilities for using these characteristics as a means for determining fossil age are frustrated by variations of the amino acid pattern among individual living organisms of the same species, and by the critical dependency of the racemization probability for an amino acid molecule on temperature, water concentration in the environment, alkalinity of the environment, association with other molecules (free state or a component of a macromolecule), size of the macromolecule of which it may be a component, specific location in the structure of a macromolecule, catalytic effect of clay surfaces with which it may be associated, presence of aldehydes and metal ions, concentration of buffer compounds in the environment, and ionic strength of the environment.In spite of these complications, fossils of similar characteristics, and which have experienced similar conditions of preservation, can be placed in a relative age sequence on the basis of D/L ratios.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.The instability of the twenty amino acids which are the building blocks of proteins provides a possible means for determining the ages of fossils.A preliminary recognition of this possibility appeared in the scientific literature 30 years ago (Abelson 1955).So the process of racemization looks like a good candidate for one of nature's clocks.