| Abstract: |
Isotopes of an element all have the same number of electrons and protons, but different in the number of neutrons in their nuclei. This causes isotopes to have different masses. The 15N/14N ratio of nitrogen in bone collagen (the product) is different from the ratio in all the nitrogen in the animal's diet and breakdown products (the substrate). Bone collagen normally has realtively more 15N than in is in the diet because relatively more 14N is excreted. \bSubstrate\b: The starting components or source of a chemical reaction involving stable isotopes of element. For example, the food that an animal eats is a substrate
the ocean is th source of atmospheric carbon. \bReaction\b: The process by which stable isotopes are altered. For example, digestion and enzyme processes, photosynthesis, etc. \bReaction rate\b: The speed at which chemical bonds break among isotopes of an element. The smaller the number of neutrons, that is, the lighter the mass of the isotope the faster the reaction rate, For example, <sup>12<\sup>C reacts faster than <sup>13<\sup>C. \bProduct\b: The result of a reaction on a substrate. For example, bone collagen (the product) is the result of enzyme reaction on food (the substrate). \bFractionation\b: The difference between stable isotopic ratios in product and substrate. That is, due to a reaction on he substrate, the isotopes of an element may be found in different proportions in the product. \bKinetic isotope fractionation\b: Fractionation in which the reaction is caused by the addition of biochemical properties. \bEquilibrium isotope fractionation\b: Fractionation in which the reaction is caused by a physical property, such as temperature, evaporation, evapotranspiration. Stable isotope ratios serve as probes of various aspects of paleoecology and human behavior, and thus provide additional understanding of events that are documented by other paleoanthropological and bioarchaeological studies. things that can be tested: temperature and humidity by O plant cover by C migration patterns by Sr diet by C, N, S (but sulfur as very little in bone tissue). The C source for all terrestrial plants is atmospheric CO2. During the transfer of CO2 from the atmosphere to plant tissue there is a further depletion of 13C through kinetic isotope fractionation during photosynthesis. Plant delta<sup>13<\sup>C values are determined by the photosynthetic pathway as well as by source carbon. The pathways are commonly referred to a C3, C4, and the less common Crassulacean Acid Metabolism (CAM), which was identified in an is mainly studied in succulents. In most areas of the world, marine vertebrates have delta<sup>15<\sup>N values that are 6-8 more postive than are the values in terrestrial vertebrates at similar trophic levels. \bUsing Hydrogen isotope ratios: D/H (deltaD)\b can be used to track the amount of relative humidity during specific time period which would be an indication of climatic cooling if there is a decrease. \bOxygen Isotope ratios: delta\+18\+O\b like H, values vary due to temperature bone and tooth enamel phosphate shows promise. Among mammals that obtain their water by drinking, the oxygen isotope ratios in bone phosphate associate linearly with the ratio in rainwater. In addition, ratios obtained from human tooth enamel have been shown to very with latitude. Animals that obtain the significant amount of their body water from leaves have delta\+18\+O that vary with average humidity. \bDiagenesis\b More than 90% of the organic matric is the protein collagen with up to 8% of tooth and bone weight is carbonate. Bone mineral carbonate is in equilibrium with CO\-2\- dissolved in blood and thus should reflect the total metabolic carbon pool which consists of diet plus tissue breakdown products. Collagen however, should predominately reflect the protein and, to a lesser extent, the carbohydrate fraction. The carbon in soil carbonates and paleosol organic matter canserve as ecological indicators. Soil carbonate delta<sup>13<\sup>C reflects the dissolved carbonate components in groundwater, which, in turn, reflects the plant biomass at the time of soil formation. Soil organics also record the carbon isotope ratio of the plant cover. In most cases, the O isotope record is better preserved in phosphates than in carbonates, although enamel must be screened to assure its integrity. \bApplications\b \uIntroduction to Agriculture\u origins of domestication adoption of maize adoption of millet change from marine fishing an gathering to complete dependence on terrestrial food sources domestication of beans \uSocial and economic implications of diet differences\u status \uUse of aquatic resources\u certain time period are associated with a significant reduction in dependence on marine fish. distinguishing between the use of shallow-water fish and invertebrates veruss deep-ocean fish and mammals. \bDiet composition, energentics, and the question of omnivory\b Because of the recognized associations among diet composition, subsistence strategy, and behavior, one goal of stable isotope studies has been to estimate the relative contribution of various food in diet. The approaches used have been mass balance equations, comparisons of human delta<sup>15<\sup>N values with those of carnivores and herbivores, and determination of the realtive spacing between the delta<sup>13<\sup>C value in bone collagen and that in bone apatite carbonate. In its simplest form, a mass balance equation assumes that the delta value of the diet is equal to a weighted average of the delta values of the various diet components. Thus, a diet consisting of 30% squash and beans plus 70% maize would have a delta<sup>13<\sup>C value reflecting 30% C\-3\- and 70% C\-4\-. Fractionation between diet and bone collagen is not constant across diets. During metabolism, the bonds in amino acids containing <sup>14<\sup>N break more readily than those containing <sup>15<\sup>N. The results is that during energy metabolism a greater quantity of amino acids containing <sup>14<\sup>N are bren down and the nitrogen is excreted as urea, which is depleted in <sup>15<\sup>N. As a consequence, the dietary amino acids available for protein synthesis are enriched in <sup>15<\sup>N. While there food intake may be similar, if more energy is expended/day the one with have higher \+\+N values. Another way is by loing at the different levels of <sup>13<\sup>C by comparing collagen and carbonate levels. Because lipids and carbohydrates have significantly different <sup>13<\sup>C values, carnivores and herbivores are expected to differ in their bone carbonate delta<sup>13<\sup>C values when these values are standardized by comparison to the values from bone collagen. The offset is often represented as delta<sup>13<\sup>Coll-carb. \bEarly hominid evolution\b
|
