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Amino acid dating techniques

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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.The most reliable of the complex network of diagenetic reactions is amino acid racemization, which involves the interconversion of L-amino acids to their D-isomeric configurations.

The technique is inexpensive, rapid, and can be applied to fossils as small as single ostracode or foraminifer test.Two general approaches are used to convert D/L ratios to an absolute time scale: The first is a calibrated approach in which the D/L ratios are used to interpolate between, or extrapolate beyond, the known ages of independently dated samples within a restricted geographic/ oceanographic area, where temperature histories are similar.In the second approach, the effects of time and temperature on the extent of racemization are determined in modern shells subjected to high-temperature laboratory experiments, and in Holocene samples whose ages are known from 14C analysis and whose temperature history can be inferred based on instrumental data. R., eds., Quaternary geochronology: methods and applications, American Geophysical Union, Washington D. For example, a kinetic model is used to estimate the age of an undated sample by extrapolating beyond a calibration point, or a calibration curve developed for one thermal regime is applied to another using a kinetic model to adjust the reaction rate for differences in site temperature. F., 1993, Applications of organic geochemistry for Quaternary research; Aminostratigraphy and aminochronology, in Engel, M. A., eds., Organic Geochemistry: New York, Plenum Press, 755-783. Because the extent of racemization is dependent on both temperature and time, the average postdepositional temperature ("effective diagenetic temperature"; Wehmiller, 1977) can be determined from the D/L ratio if the sample age is known independently. Amino acid studies of the Del Mar, California, midden site—Apparent rate constants, ground temperature models, and chronological implications. Amino acid racemization (or ) in fossils is interpreted in terms of relative ages.