Amino acid dating techniques


15-Feb-2017 10:08

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.(For it would be strange and anti-scientific to conjecture that the rate of racemization of the shells in the Arctic mud is constant whenever we can check it, but variable when we can't.) Just this was established by Kaufman et. (2008) in their paper Dating late Quaternary planktonic foraminifer Neogloboquadrina pachyderma from the Arctic Ocean by using amino acid racemization, Paleoceanography, 23(3).It gives the reader some idea of the difficulties of the method that they were obliged to use the single common foram species N.But after its death, the amino acids can spontaneously change their chirality, flipping from being left-handed to right-handed, and indeed back again.The result of this process is that eventually the amino acids will collectively become racemic: each particular amino acid will have one chirality or another, but after a sufficient amount of time, collectively the amino acids won't favor one enantiomer over another. We should note that although the underlying basis for this process is random, and that in principle the amino acids could by some statistical fluctuation become less racemic and more chiral, the laws of statistics ensure that in practice if we are looking at a large enough sample of amino acids, the chances are astronomically remote that such a thing will occur.An attempt to account for these apparently anomalous observations has been made by suggesting that the fossil matrix somehow holds the amino acid molecules together so that they do not spontaneously decompose as would be expected on the basis of their binding energies (i.e., structural strength) (Hare and Mitterer 1968).

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All this is not to say that the reader should dismiss out of hand results obtained by amino acid dating; but it can be trusted only when the people applying it have taken care to ensure that they are using it in a context in which it is known to work.

pachyderma, having found that racemization rates differed even between different species of forams.