Relation of Age Estimation and Forensic Science

Age estimation is important in the field of forensic science because the estimation can tell investigators the person’s birth date, age of death and the year of death. These information together with the person’s bone structure, gender etc. can help the investigators narrow down the possible matches towards the deceased. The paper pointed out that traditional anthropologist methods of identifying morphology is usually imprecise when compared to chemical analysis of the tooth dentin when it comes to estimating ages.

Traditional Morphological Methods vs Racemization of Amino Acids/ Radiocarbon Dating

The researchers of the paper claimed that the traditional morphological methods (radiological examination of skeletal and dental development) is used when determining the age in children and adolescents. This method, however, does not happen to be very accurate in adults. There are more complex methods to estimate age in adults, and these methods happen to be more accurate than the traditional methods. Alkass et. al pointed out that “racemization of aspartic acid in dentin/tooth enamel or radiocarbon dating of tooth enamel” leads to “high precision age estimation” [1022]. Some statistics they gave comparing traditional morphological methods vs aspartic acid racemization/ radiocarbon analysis: ~10 years vs ~3 years/ ~1-2 years.

What is the Relation of Amino Acids and Estimating Age?

Amino acids can occur in 2 forms: L- and D- forms (enantiomers). Enantiomers are mirror images that are not superimposable- like the right and left hand. Only the L-forms are used by cells. When humans age, L-forms amino acids will transform into D-forms via the process racemization. So we can make use of this fact to estimate age. The researchers said that it would take ~100,000 years for all L-form to transform into D-form at a temperature of 25 Celsius! Furthermore, tissues with lower metabolic rates would be better used for age estimation due to the continuous synthesizing and degradation of amino acids in the human body. With this in mind, teeth would be a tissue with a low metabolic rate and usually they are, like bones, are preserved better than other body tissues when the “post-mortem” interval is long [1022].

What is Radiocarbon Dating?

Known more commonly as Carbon-14 dating. Radiocarbon dating of the tooth enamel provided high precision to determine the date of birth of an individual. The concept of half-live is used.

More information on carbon-dating:

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

The Experiment: A Swedish Homicide

A human skeleton was discovered in a Swedish forest in summer 2006. Since the forensic anthropologist could not determine the year of death precisely, the newer/ more accurate methods were used. They extracted 4 teeth from the skeleton. Dentin was used for the racemization of aspartic acid. Gas chromatography was used. The estimation of age was used to determine the D/L ratio. C-14 dating was also used for determining the year of birth. Note: bomb spike radiocarbon levels indicates individual is born before 1955.

Fig.1 

The comparison of correlation of accuracy of the 2 methods of Year of Birth. Carbon-14 dating shows better estimation of the year of birth.
Combined analysis of radiocarbon and aspartic acid racemization on teeth collected from the Swedish homicide case. A third molar with enamel laydown time of 13 years showed victim was born 1942. Average age was estimated from aspartic acid racemization of  46.8 years and the date of death was calculated, which is 1988.8.

Conclusion

The take home message here is that we can use amino acid racemization to determine the year of birth and year of death of a person. It is related to proteomics because it is important to understand how the proteins work and how the amino acids racemize as a person ages. It is also important to know figure out which amino acids to use and how to extract them from the proteins of interest. For example, in this paper, the researchers extracted L and D forms aspartic acid with gas chromatography/ MS and determined the tooth formation with accelerated mass spectrometry. This method is commonly used because it is independent of the bomb spike and can be used to determine age for the individuals that were born before the nuclear testing.

References