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Amino acid dating fossils

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The rate at which racemization proceeds depends on the type of amino acid and on the average temperature, humidity, acidity (p H), and other characteristics of the enclosing matrix.Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization.These effects restrict amino acid chronologies to materials with known environmental histories and/or relative intercomparisons with other dating methods.Temperature and humidity histories of microenvironments are being produced at ever increasing rates as technologies advance and technologists accumulate data.

The possibilities for using these characteristics as a means for determining fossil age are frustrated by variations of the amino acid pattern among individual living organisms of the same species, and by the critical dependency of the racemization probability for an amino acid molecule on temperature, water concentration in the environment, alkalinity of the environment, association with other molecules (free state or a component of a macromolecule), size of the macromolecule of which it may be a component, specific location in the structure of a macromolecule, catalytic effect of clay surfaces with which it may be associated, presence of aldehydes and metal ions, concentration of buffer compounds in the environment, and ionic strength of the environment.

These are also preserved in sediments which accumulated as a response to global climatic pulses, during the Pleistocene and beyond.

Therefore, amino acid geochronology has the potential to be widely applicable to the chronology of human evolution, as well as to the geological record.

In spite of these complications, fossils of similar characteristics, and which have experienced similar conditions of preservation, can be placed in a relative age sequence on the basis of D/L ratios.

Due to the strong dependency of racemization rates on temperature, water concentration, and alkalinity, uncertainties regarding conditions of preservation can leave amino-acid-based age relationships among even similar fossils open to question.