After synthesis by an organism, proteins and their constituent amino acids degrade through a complex series of biogeochemical reactions (Mitterer, 1993).The extent to which these reactions have progressed in a fossil is proportional to the length of time elapsed since the organism lived and to the ambient temperature of the reaction medium.
It is particularly useful for fossiliferous deposits beyond the range of 14C dating (older than about 40,000 years), for which few alternative geochronological tools are available.
(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.
Each sample should comprise a collection of at least five monogeneric shells.
For ion exchange analysis, the minimum sample size for each shell (or group of shells or shell fragments) is ~20 mg.
For example, a shoe is chiral: you cannot turn a left-foot shoe into a right-foot shoe by turning it round or flipping it over.