Amino Acid Racemisation (AAR) is a useful comparative dating method with great potential, but it introduces problems of calibration and the requirement of an intimate knowledge of the palaeoenvironmental conditions of the bone deposition site.
Table-1: The hominid fossil record is extremely fragmentary, and chronology is essential in unravelling the complex record of human development.
Therefore outside Scandinavia it is difficult to find continuous sequence of varves reaching the present.
The longest sequence known goes back only 17,000 years.
the 'fossil' tracks counted) viz., exposes the sample to a known number of low energy (thermal)neutrons which induce fission of a small fraction of the uranium atoms in the sample.
This is based on the fact that all living organisms have L-amino acid in their protein and after death, and over a long period of time all the L-amino acids except glycine undergo change called racemisation and became non protein D-amino acid.
In fact, chronology is one of the most fundamental issues in and perhaps a characteristic of archaeology.
Archaeologists use several methods to assign ages to events of the past.
Fission Track Technique - This technique dates material ranging from 20 years to 1,000,000,000 years before the present.
Fission track dating is based upon the fact that over geological time spontaneous fission of uranium-238 impurities produces minute sub- microscopic damage trails in the most insulating solids, both long period of time.
They are engaged in defining the stages of hominid evolution and their artifactual record, and the assignment of a chronology to these stages.