Amino Acid Racemisation And Carbon 14 Dating Result - Case Study Example

Name : xxxxxx Tutor : xxxxxx Title : Amino Acid Racemisation and Carbon 14 Dating result Course : xxxxxx Institution : xxxxxx @ 2010 Carbon -14 Carbon 14 dating is method that relies on radioisotope of carbon -14 that occurs naturally in estimating the age of organic materials remains between the ages of 58,000 and 62,000 years from archaeological sites. The coast al height changes laterally over short distance. This may be due to fluctuations in the sea level or a reflection of changeover within the depositional surrounding. The terrace appears in different high points above the current sea level. Investigation on the age of the reef units reveal that the youngest unit is between 86,000 and 118,000 years B.P. In this period, three reef cycles have occurred with the middle formation occurring in 205,000 years and the oldest age approximated to be between 290,000 and 340,000 years B.P. Table 1 Samples detail and results for Radiocarbon dating Lap no Sample no Height (cm) δ13CVPDB‰ ± 0.2 Age (BP) Wk-26593 1.1.13 120 3.1 2362 ± 41 Wk-26594 1.2.7 270 0.8 40.180 ± 961 Wk-26595 2.1.2 0 2.7 < 45488 Wk-26596 2.2.4 320 3.0 53.019 ± 3623 Wk-26597 4.2.1 230 2.2 43.568 ± 1500 Physical observations that are not dependent on the geochonological proof usually give steady lower age boundaries for the terraces and avail more constraints for the explanation. Examining the association between the location of the terraces and position of major tectonic structures in the region suggests the absence of recent activity of the previously recognized faults. Behairy (1982) demonstrated four major marine transgressions using the radiometric ages of the corals in the terraces. Before the 31,000 years B.P, the interstadial period is when the first transgression was reported and it’s the time the coral formation was favored and the climatic condition are said to be the same as the current times. The second transgression occurred between 40,000- 26,000 years B.P. during this period the water level were said to be at its maximum( Behairy, 1982). The highest sea level rise was recorded between the 16,600 and 18,000 years B.P where over 15 meters above sea level. The sea level dropped after 16,600 years and this supported by existence of aragonite layers in red sea sediments dumped in the range of 11,000 years – 20,000 years B.P. the layers are attributed to be the outcome of the lowering ea level resulting in the hypersaline setting in the red sea. The third transgression is reported to have occurred in ages of 9980 years B.P and it is of shorter duration, evidence show an early Holocene drop in level to 4meters below the current southeast coastline. The fourth marine transgression is characterized by 1meter above the present level of the sea level. The interglacial fluctuations and associated terraces are found either below or close to the present sea level. As a result of the tectonic movements, the current elevations or the marine terraced are above the recent sea level. These findings are found to be wrong and further research that will incorporating calibration methods that captures the high calibration confidence level. Chapel (1974) suggested Quaternary sea-level variation models of acknowledged comprehensive applicability that characterize a structure for the ages and spatial distribution of the Pleistocene coastal sediments. Generally it is acknowledged that marginal sediments of Holocene age occur widely around the shoreline. Amino Acid Racemisation This is a technique that approximates the age of a sample by relating the changes in amino acid molecules to the elapsed time since its formation. For the results obtained an analysis of the relationship between changes in the amino acid molecules is determined. All organic tissues have amino acids which have an asymmetric carbon atom except glycerin thus they have two different configurations, “D” or “L”. Existing organisms have their amino acids in “L” configuration and when the organism dies, the pattern management ceases and the ratio D/L shift slowly near equilibrium and this process is called racemization and this process allows for the measurement of the period the specimen has died. From the results of the 5bivalves shell samples; the D/L ratios are represented in table 2 below. Table 2: Results of D/L ratios D/L ratios Sample Aspx Glx Ser Vax Ala 7900 0.55 0.83 0 0.78 0.75 7902 0.78 0.90 0 0.91 0.89 7903 0.72 0.62 0 0.52 0.60 7904 0.78 0.96 0 1.03 0.76 Table 3 Comparison of the D/L values with the results from Kaufman (1998) D/L ratios from table 2 D/L ratios from Kaufman (1998) Aspx Glx Asp Gl 0.55 0.83 0.33 0.12 0.78 0.90 0.20 0.06 0.72 0.62 0.19 0.03 0.78 0.96 0.18 0.04 Comparing the results obtained in table 2 and those obtained in table 3 by Kaufman (1998). Figure 1 shows the comparison of the D/L ratios and from the analysis the ontogenic trends in D/L Aspx values are parallel by the uniqueness of the shell amino acids. The higher rate of racemization in Aspx is associated with lower concentrations of the total amino acids and higher comparative concentrations of the amino acids. Figure 1: Comparison between the D/L ratios The results obtained may not be considered to be good due to the weaknesses associated with racemization. Racemization depends on temperature, alkalinity, concentration of water, preservation conditions that may leave the amino acid dating questionable. Presently there is inadequate knowledge on the effective average racemization rate in a fossil as function of time to allow the dependency on the D/L ratio for the determining age quantitatively. (Brown, 1985). There are cases where the extrapolation of the rate constants from soaring temperature racemization in the laboratory have yielded logical age estimate in conformity with the agreed geochronological age of a fossil( for example., Hare and Mitterer, 1968). From the results obtained in Figure 1 and table 4; it is obvious that for any specific amino acid present, there is no typical racemization constant that is applicable for all ordinary circumstances. It can be affirmed that the factors that determine the racemization rate of amino acids (Smith and Evans 1980, Kriausakul and Mitterer 1980a, 1980b ) include , size of macromolecule, Ionic strength of the environment specific location in the molecule, bound state versus free state , contact with clay surfaces( catalytic effect), Presence of aldehydes, particularly when associated with metal ions, Concentration of buffer compounds , water concentration and pH in the environment, temperature. In a fossil, the D/L ratio symbolizes the age and the environmental conditions under which it has been preserved. Table 4:D/L ratio of the 5bivalves shell samples The results in table 4 capture the compares with the analysis reported by Goodfriend (2001), HPLC analysis were carried to determine evidence of the changes in protein chemistry by ontogeny that may elucidate the ontopogenetic trend in Asp racemization rates. The geochemistry trends within cells of the amino acids might be related to digenetic amendments. The stability of amino acids varies (Vallentyne, 1969). Groenen et al., (1990) affirm that the rates of racemization in protein (amino acids) vary according to their position in the protein. The dissimilarity in the composition of the protein more often direct variation in the racemization rate measured amino acids ensemble and these yield patterns of orthogenetic variation in Asp racemization rate observed. The position of the amino acid peptide protein also contributes to the rate variation. The real time-age of the fossil can be derived from a D/L ratio and equivalent racemization rate constant is determined and as long as the environmental factors that are significant are specified. “The present status of amino acid dating can be summarized by the conclusion from the 19th International Symposium on Archeometry and Archaeological Prospection that "the time when [amino acid racemization] can provide a problem-free dating service is still some way off". The literature since 1979 indicates an increasing awareness of the uncertainties in using amino acid D/L ratios as indicators of age.” (Hedges 1979). Reference Chappell, J. (1974). Geology of coral terraces, Huon Peninsula, New Guinea: A study of Quaternary tectonic movements and sea level changes. Geological Society of America Bulletin, 85, 553-570. Hare, P. E. and R. M. Mitterer. 1968. Laboratory simulation of amino acid diagenesis in fossils. Carnegie Institution of Washington Year Book 67 (1967-1968), pp. 205-208. Hedges, Robert. 1979. Physics in archaeology. Nature 278:691, 692. Kriausakul, Nivat and Richard M. Mitterer. 1980a. Comparison of isoleucine epimerization in a model depeptide and fossil protein. Geochimica et Cosmochimica Acta 44:753-758. Miller, Gifford H. and Hare, P. E. 1980. Amino acid geochronology: integrity of the carbonate matrix and potential of molluscan fossils. In Hare et al. 1980, pp. 415-443. Plastino, W.; Kaihola,L.; Bartolomei, P.; Bella, F. (2001) . “Cosmic background reduction in the radiocarbon measurement by scintillation spectrometry at the underground laboratory of Gran Sasso” Radiocarbon 43 (2A): 157-161. R. H. Brown (1985) Can reliable age determinations be based on fossil amino acid data? Geoscience Research Institute . Origins 12(1):8-25 (1985). Smith, Grant Gil and Robert C. Evans. 1980. The effect of structure and conditions on the rate of racemization of free and bound amino acids. In Hare et al. 1980, pp. 257-282. Vallentyne, J. R. (1969) Pyrolysis of amino acids in Pleistocene Mercenaria shells. Geochim. Cosmochim. Acta 33, 1453–1458. Wolf-Christian Dullo, Erlangen ;( 1990) Facies, Fossil Record, and Age of Pleistocene Reefs from the Red Sea.Evolution of reefs. Read More