Amino acid geochronology is best suited as a relative-dating tool, or as a calibrated-dating method
in conjunction with other dating techniques. It is applicable to a wide range of fossils types (mollusks, ostracodes, foraminifera, bone, egg shells, and teeth), stratigraphic problems (correlations, reworking, unconformities), depositional environments (marine, lacustrine, fluvial), and time scales (decades to millions of years). 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. The technique is inexpensive, rapid, and can be applied to fossils as small as single ostracode or foraminifer test. Amino acid racemization (or AAR
) is the interconversion of amino acids from one chiral form (the L - laevo amino acids which are the building blocks of proteins) to a mixture of L- and D- (dextro) forms. The extent of racemization is measured by the ratio of D/L isomers and increases as a function of time and temperature, and can be used for geochronology or paleothermometry.