Amino acids are the building blocks or sub-units of proteins and proteins are the richest organic molecules found in cells. Over 50% of all large organic molecules found in the cell are protein. Since they are related to whole aspects of cell structure and function, they are found in every part of every cell. Protein generally consists of 20 varying amino acids . Most amino acids in the proteins have at least one asymmetric carbon atom and that can exist in two ways. The two different forms are called L-amino acid and D-amino acid, "the L and D designating the direction in which solutions of these amino acids rotate plane-polarized light.” (L-amino acid form is extended to the left, whereas D-amino acid form is extended to the right.) Those two have mirror-images of each other, just like left and right hands.

All living organisms essentially have L (left handed) amino acids in their proteins, and after the death of the organism, the L-amino acid gradually changes to D (right-handed) amino acids by the process of racemization. Amino acids complete the racemization process when the amounts of L and D amino acids are equal. The older the sample material is, the greater the extent of racemization would be. This means the organism that has died a long time ago might have more D-amino acids than the ones that died recently. In this way, the extent of racemization process can serve as a dating technique. The ratio of L and D amino acids can be measured by gas and liquid chromatography.

Racemization is applied to organic materials (or fossil materials) such as human and animal bones, teeth, plants, ostrich egg shells, mollusks, marine sediments, freshwater and marine shells, oyster shells, carbonate shells (foraminifera, snails, clams, ostracods,) calcareous sediments and peats.

Racemization can date samples to approximately 5,000 - 100,000 years old. However, there are dates as old as 200,000 years produced by this method. It is said that Racemization can date older materials than what Carbon 14 can date. As a dating technique, racemization has practical application in the fields of Archaeology, Geochemistry, Marine Geology, Geochronology or Geoscience

Although the finding of this dating method was meaningful, this dating method is considered controversial. The rate of racemization is dependent on temperature, or the thermal history of the fossil. The rate of racemization increases at warmer sites than at cooler sites. Samples from areas of different latitude tend to have greater age range differences. To obtain accurate dates, the temperature has to be constant for thousands of years. The speed of racemization slows down if the sample materials gets cold. The study carried out with bone revealed that unassured temperature of plus or minus 2 degree will cause an plus or minus 50% error of the age.

Amino acid dating can not obtain the age of the material purely from the data itself. The rate of racemization can not be standardized by itself because it is too changeable. Thus, because of the rate problem, this dating technique must rely on other dating techniques to standardize its findings. As a matter of fact, the ages obtained from racemization dating must rely on other techniques such as Carbon 14, and if the dating of Carbon 14 is not accurate, racemization dating can never be certain.

Materials can easily be contaminated. Sample material can lose or gain amino acids by leaching, diagenetic formation of amino acids, bacterial contamination, and/or contaminated during collection or preparation. If the materials are contaminated by water, their racemic clocks will be ruined. Even though there must be some moisture for the occurrence of racemization, continual inflow of moisture can cause many kinds of contamination. For example, if pH of the moisture is higher, the racemization process would be very rapid, and that changes the age of the sample.

Bibliography

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http://www.creation-science-prophecy.com/amino “Amino Acid Dating. Is it reliable?” Mike’s Origins Resource: Creation Science, Prophecy, Biblical Evidence. (August 14, 2000) September 28, 2000.

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Written by Kozue Takahashi