Amino acid dating fossils
The ratio increases with time and temperature until the rate of formation of D-amino acids is compensated by the reverse reaction, and the ratio reaches an equilibrium value of 1.0.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.Unlike many other proxy indicators of paleoclimate, amino acid paleothermometry is based on processes that are independent of precipitation changes, and therefore allow paleotemperatures to be calculated uniquely.
This relation, together with a model of racemization kinetics, is used to calculate the age of a sample if its D/L ratio and temperature history are known. Aminostratigraphic dating methods in Quaternary geology, in Noller, J.
The technique is inexpensive, rapid, and can be applied to fossils as small as single ostracode or foraminifer test.
Amino acid racemization (or ) in fossils is interpreted in terms of relative ages.
As a rule of thumb, sites with a mean annual temperature of 30°C have a maximum range of 200 ka and resolution of about 10 ka; sites at 10°C have a maximum age range of ~2 m.y., and resolution generally about 20% of the age; at -10°C the reaction has a maximum age of ~10 m.y., and a correspondingly coarser resolution.
Because the rate of amino acid racemization is controlled by the temperature experienced by the fossil since burial (rather than when it was living), an evaluation of site temperature is required for geochronological interpretation.
For reverse phase, minimum sample size is for geological purposes have been summarized by Miller and Brigham-Grette (1989), Wehmiller (1993), Rutter and Blackwell (1995), and Wehmiller and Miller (2000), among others.