Amino acid dating

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Amino acid dating is a

sedimentary geology and other fields. This technique relates changes in amino acid molecules to the time elapsed since they were formed.[1][2][3][4][5]

All biological tissues contain

optically active, having a stereocenter at their α-C atom. This means that the amino acid can have two different configurations, "D" or "L" which are mirror images of each other. With a few important exceptions, living organisms keep all their amino acids in the "L" configuration. When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization. Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.[6]

Factors affecting racemization

The rate at which racemization proceeds depends on the type of amino acid and on the average temperature, humidity, acidity (pH), 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. These are important for amino acid dating because racemization occurs much faster in warm, wet conditions compared to cold, dry conditions. Temperate to cold region studies are much more common than tropical studies, and the steady cold of the ocean floor or the dry interior of bones and shells have contributed most to the accumulation of racemization dating data. 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 Ma, and resolution generally about 20% of the age; at -10 °C the reaction has a maximum age of ~10 Ma, and a correspondingly coarser resolution.[6]

Strong acidity and mild to strong alkalinity induce greatly increased racemization rates. Generally, they are not assumed to have a great impact in the natural environment, though tephrochronological data may shed new light on this variable.

The enclosing matrix is probably the most difficult variable in amino acid dating. This includes racemization rate variation among species and organs, and is affected by the depth of decomposition, porosity, and

catalytic
effects of local metals and minerals.

Amino acids used

Conventional racemization analysis tends to report a D-alloisoleucine / L-isoleucine (A/I or D/L ratio). This amino acid ratio has the advantages of being relatively easy to measure and being chronologically useful through the Quaternary.[7]

Reversed phase HPLC techniques can measure up to 9 amino acids useful in geochronology over different time scales on a single chromatogram (aspartic acid, glutamic acid, serine, alanine, arginine, tyrosine, valine, phenylalanine, leucine).[8][9][10]

In recent years there have been successful efforts to examine intra-crystalline amino acids separately as they have been shown to improve results in some cases.[11]

Applications

Data from the geochronological analysis of amino acid racemization has been building for thirty-five years.

paleogeography, paleobiology, and paleoclimatology have been particularly affected. Their applications include dating correlation, relative dating, sedimentation rate analysis, sediment transport studies,[12] conservation paleobiology,[13] taphonomy and time-averaging,[14][15][16] sea level determinations, and thermal history reconstructions.[17][18][19][20]

radiocarbon and other dating techniques by amino acid racemization and vice versa has occurred.[21] The 'filling in' of large probability ranges, such as with radiocarbon reservoir effects, has sometimes been possible. Paleopathology and dietary selection, paleozoogeography and indigeneity, taxonomy and taphonomy
, and DNA viability studies abound. The differentiation of cooked from uncooked bone, shell, and residue is sometimes possible. Human cultural changes and their effects on local ecologies have been assessed using this technique.

The slight reduction in this[clarification needed] repair capability during aging is important to studies of longevity and old age tissue breakdown disorders, and allows the determination of age of living animals.

Amino acid racemization also has a role in tissue and protein degradation studies, particularly useful in developing museum preservation methods. These have produced models of protein adhesive and other biopolymer deteriorations and the concurrent pore system development.

Forensic science can use this technique to estimate the age of a cadaver[22] or an objet d'art to determine authenticity.

Procedure

Amino acid racemization analysis consists of sample preparation, isolation of the amino acid wanted, and measure of its D:L ratio. Sample preparation entails the identification, raw extraction, and separation of proteins into their constituent amino acids, typically by grinding followed by acid hydrolysis. The amino acid derivative

cation, and the D:L ratio determined by mass spectrometry
. Chromatographic and electrophoretic separation of proteins and amino acids is dependent upon molecular size, which generally corresponds to molecular weight, and to a lesser extent upon shape and charge.

References

  1. doi:10.1146/annurev.ea.13.050185.001325
    .
  2. doi:10.1002/kin.10153
    .
  3. PMID 11539479
    .
  4. ^
    doi:10.1111/j.1475-4754.1997.tb00806.x
    .
  5. ^ Scarponi D, Kaufman D, Bright J, Kowalewski M (October 2008). "Quantifying time-averaging in 4th-order depositional sequences: radiocarbon-calibrated amino-acid racemization dating of Late Quaternary mollusk shells from Po Plain, Italy". Geological Society of America Abstracts with Programs. 40 (6): 502. Archived from the original on 2015-01-22. The results provide a compelling case for applicability of amino acid racemization methods as a tool for evaluating changes in depositional dynamics, sedimentation rates, time-averaging, temporal resolution of the fossil record, and taphonomic overprints across sequence stratigraphic cycles.
  6. ^ a b "Method". Amino acid geochronology laboratory. Northern Arizona University. Archived from the original on 2 October 2016.
  7. ^ "NEaar: North East Amino Acid Racemization". University of York.
  8. doi:10.1016/S0277-3791(97)00086-3
    .
  9. ^ Kaufman DS (2000). Perspectives in Amino Acid and Protein Geochemistry. New York: Oxford University Press. pp. 145–160.
  10. ^ "Method". Amino Acid Geochronology Laboratory. Northern Arizona University.
  11. PMID 19684879
    .
  12. doi:10.1130/G23722A.1
    .
  13. doi:10.1130/0091-7613(2000)28<1059:DDFPTT>2.0.CO;2
    .
  14. S2CID 131237779
    .
  15. doi:10.1130/G21607.1
    .
  16. S2CID 5839861
    .
  17. doi:10.1016/0277-3791(87)90016-3
    .
  18. doi:10.1130/0016-7606(1996)108<0892:AAEOLT>2.3.CO;2
    .
  19. S2CID 4312380
    .
  20. doi:10.1016/S0277-3791(03)00006-4
    .
  21. doi:10.1016/0033-5894(82)90068-0
    .
  22. S2CID 8664035
    .

External links

The Wikibook Historical Geology has a page on the topic of: Amino acid dating

Active laboratories

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