A comparative study of the kinetics of amino acid racemization/epimerization in fossil and modern mollusk shells
- Weizmann Inst. of Science, Rehovot (Israel) Carnegie Inst. of Washington, Washington DC (United States)
- Univ. Bern (Switzerland)
The present study examines the question of whether heating experiments on modern shell material accurately model the pattern of kinetics of racemization/epimerization in fossils. Using one modern sample and four fossil samples (dating to 9700-1700 yr B.P.) of a species of land snail from the Negev Desert, the kinetic behavior of the samples in laboratory heating experiments are compared. Results are then compared to the Holocene trend in kinetic patterns observed in a large series of radio-carbon-dated shells. For most amino acids (alanine, alloisoleucine/isoleucine, phenylalanine, and glutamic acid), the fossil material displays the same pattern of kinetics in relation to time as the modern shells; deviant patterns are observed for aspartic acid, proline, and methionine. Adherence to a first order kinetic pattern in heated shells occurs only in alloisoleucine/isoleucine (within the range of D/L ratios studied). Differences in the temperature dependence of racemization/epimerization rates are found between modern and fossil samples. In most cases this relationship when extrapolated to natural temperatures, does not agree well with observed rates of racemization/epimerization in the fossil series. However the pattern of change in rate of racemization/epimerization with time in heating experiments generally follows the trend observed in the fossil series rather well. The experiments indicate that heating experiment results for certain amino acids, such as the widely used alloisoleucine/isoleucine, do give good predictions of kinetic patterns in relation to time in fossils but that predictions of the temperature dependence of rates are less accurate.
- OSTI ID:
- 5211804
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 55:11; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMINO ACIDS
RACEMIZATION
THERMODYNAMIC ACTIVITY
FOSSILS
AGE ESTIMATION
DIAGENESIS
COMPARATIVE EVALUATIONS
EXOSKELETON
GEOLOGIC HISTORY
MOLLUSCS
REACTION KINETICS
SEDIMENTARY ROCKS
STEREOCHEMISTRY
TEMPERATURE EFFECTS
ANIMALS
AQUATIC ORGANISMS
BODY
CARBOXYLIC ACIDS
EVALUATION
INVERTEBRATES
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
ROCKS
SKELETON
580000* - Geosciences