Radiocarbon

By measuring Ihe l isoleucme/o alloisoleucme ralio m Ihe prolem isolated from Ihe eggshells of an exlincl Auslrahan bird a team of scienlisls recenlly determined lhal Ihis bird lived approximately 50 000 years ago Radiocarbon ( " C) dalmg is nol accurate for samples older lhan aboul 35 000 years so AAR is a useful addilion lo Ihe fools avail able lo paleonlologisls... 

Radiocarbon dating (43) has probably gained the widest general recognition (see Radioisotopes). Developed in the late 1940s, it depends on the formation of the radioactive isotope and its decay, with a half-life of 5730 yr. After forms in the upper stratosphere through nuclear reactions of... 

Dating of textiles is possible by means of radiocarbon dating. Developments in this technique have greatly improved its utihty for that purpose, as exemplified by its appHcation in the dating of the Turin Shroud (121). 

By measuring the L-isoleucine/o-alloisoleucine ratio in the protein isolated from the eggshells of an extinct Australian bird, a team of scientists recently determined that this bird lived approximately 50,000 years ago. Radiocarbon ( " C) dating is not accurate for samples older than about 35,000 years, so AAR is a useful addition to the tools available to paleontologists. 

The constant half-life of a nuclide is used to determine the ages of archaeological artifacts. In isotopic dating, we measure the activity of the radioactive isotopes that they contain. Isotopes used for dating objects include uranium-238, potassium-40, and tritium. However, the most important example is radiocarbon dating, which uses the decay of carbon-14, for which the half-life is 5730 a. 

Nuclear testing has increased the amount of carbon-14 in the air, and sensitive radiocarbon dating techniques take this increase into account. 

At the top of the atmosphere, more properly at altitudes where the density is sufficiently low, high-energy cosmic ray particles cause nuclear chemical reactions with important products. The production of radioactive (or radiocarbon) already has been mentioned. 

Ostlund, H. G., Dorsey, H. G. and Rooth, C. G. (1974). GEOSECS North Atlantic radiocarbon and tritium results. Earth Planet. Sci. Lett. 23,69-86. 

The content of the material in a carbon reservoir is a measure of that reservoir s direct or indirect exchange rate with the atmosphere, although variations in solar also create variations in atmospheric content activity (Stuiver and Quay, 1980, 1981). Geologically important reservoirs (i.e., carbonate rocks and fossil carbon) contain no radiocarbon because the turnover times of these reservoirs are much longer than the isotope s half-life. The distribution of is used in studies of ocean circulation, soil sciences, and studies of the terrestrial biosphere. 

Throughout this chapter many of the arguments are based on an assumption of steady state. Before the agricultural and industrial revolutions, the carbon cycle presumably was in a quasi-balanced state. Natural variations still occur in this unperturbed environment the Little Ice Age, 300-400 years ago, may have influenced the carbon cycle. The production rate of varies on time scales of decades and centuries (Stuiver and Quay, 1980,1981), implying that the pre-industrial radiocarbon distribution may not have been in steady state. 

Fossil fuel emissions alter the isotopic composition of atmospheric carbon, since they contain no C and are depleted in C. Releasing radiocarbon-free CO2 to the atmosphere dilutes the atmospheric C content, 3delding lower C/C ratios ("the Suess effect"). From 1850 to 1954 the C/C ratio in the atmosphere decreased by 2.0 to 2.5% (Fig. 11-23) (Suess, 1965 Stuiver and Quay, 1981). Then, this downward trend in C was disrupted by a series of atmospheric nuclear tests. Many large fission explosions set off by the United States with high emission of neutrons took place in 1958 in the atmosphere and the Soviet Union held extensive tests during... 

Berner, W., Oeschger, H. and Stauffer, B. (1980). Information on the CO2 cycle from ice core studies. Radiocarbon 22,227-235. 

Craig, H. (1957b). The natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9,1-17. 

Country Deviatton from Average 6 "C/ Average July Temperature CC) Radiocarbon years BP ... 

Fallowing the radiocarbon dating conveniioTis outlined in Hedges et ol- (1993)... 

Bender, M.M. 1968 Mass spectrometry studies ofcarbon-13 variations in com and others grasses. Radiocarbon 10 468-472. 

Gillespie, R., Hedges, R.E.M. and Wand, J.O. 1984 Radiocarbon dating of bone by Accelerator Mass Spectrometry. Journal of Archaeological Science 11 165-170. 

Hedges, R.E.M., Eee-Thorp, J.A. and Tuross , N.C. 1995 Is tooth enamel earbonate a suitable material for radiocarbon dating Radiocarbon 37 285-290. 

Leavitt, S.W. andDanzer, S.R 1991 Implications of 6 C variations inCs plants over the past 55,000 years. Radiocarbon 33(2) 221. 

Hassan, A. A. 1975 Geochemical and Mineralogical Studies on Bone Material and their Implications for Radiocarbon Dating. Unpublished Ph.D. thesis, Southern Methodist University, Texas. 

Hassan, A.A. and Ortner, D.J. 1977 Inclusions in bone material as a source of error in radiocarbon dating. Archaeometry 19 131-135. 

Hassan, A. A., Termine, J.D. and Haynes, C.V. 1977 Mineralogical studies on bone apatite and their implications for radiocarbon dating. Radiocarbon 19 364-374. 

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