Fossils, radiocarbon dating

A mass of evidence seems to confirm that the mixing rate of radiocarbon in the atmosphere is rapid, and that with respect to its radiocarbon content the atmosphere can be considered as a homogeneous entirety. The contamination of samples with matter from an extraneous source can nevertheless invalidate this assumption. Two types of contamination can be differentiated physicochemical contamination and mechanical intrusion. There are two forms of physicochemical contamination. One is due to the dilution of the concentration of radiocarbon in the atmosphere by very old carbon, practically depleted of radiocarbon, released by the combustion of fossil fuel, such as coal and oil. The other is by the contamination with radiocarbon produced by nuclear bomb tests during the 1950s and later in the twentieth century. The uncertainties introduced by these forms of contamination complicate the interpretation of data obtained by the radiocarbon dating method and restrict its accuracy and the effective time range of dating. 

The basic assumption of constant atmospheric X4C activity in radiocarbon dating is not strictly valid. We now have a record of the fluctuation of atmospheric 14C variations for the last 8,400 years B.P. obtained by measurement of the isotopes of carbon in dendrochron-ologically dated wood. Prior to contamination of atmospheric 14C activity by fossil fuel combustion and nuclear technology in the 20th century, the first-order secular variation can be closely approximated by a sine curve with a period of 10,600 years and an amplitude of ... 

Bada, J. L., Master, P. M., Hoopes, E., Darling, The Dating of Fossil Bones Using Amino Acid Racemization, In Radiocarbon Dating, pp. 740-756, Berkeley, University of California Press, 1979. 

In this study, the modern and fossil bone collagen separated by dialysis is analyzed quantitatively for amino acids and the nitrogen/car-bon ratio to determine if the separated material is pure collagen or if it contains impurities which might aflEect radiocarbon dating. The fossil bone specimens with associated ages are Bison antiquus (10,000-11,000... 

In conclusion, nitrogen/carbon ratios combined with quantitative amino acid analyses could determine the level of impurities that may co-exist with fossil bone collagen and could help in selecting the optimum method of collagen separation. An extraction method may be successful in some cases but could fail to remove the impurities from bone collagen in other samples. Chemical analysis of the impurities and their radiocarbon dates also should be obtained. 

Radiocarbon dating has attracted considerable attention. Carbon-14 is produced in the upper atmosphere by cosmic-ray bombardment of nitrogen-14. It is oxidised to carbon dioxide and eventually absorbed and incorporated in the tissues of plants and animals. The time taken for a carbon atom to complete such a carbon-cycle and return to the upper atmosphere is, on average, about 500 years. As the half-life of is 5568 years, the specific activity of carbon in the carbon cycle is roughly constant. But carbon removed from this life-embracing cycle by conversion to, and retention in, a solid such as wood, bone or shell loses activity at a rate determined by the decay constant for Thus the specific activity of carbon in a rock, a fossil plant or bone, or ancient artifact gives its age (Libby, 1951). Measurements are not easy because of the low specific activities but are of considerable and improving accuracy. 

The ratio of carbon to nitrogen in a sample is used as a measure of the quality of preservation in bone and a means to determine if samples are reliable for the analysis of collagen for radiocarbon dating and dietary analysis using light isotopes. The ratio of C N in living bone is 3.2 a ratio between 2.8 and 3.5 has been suggested as indicative of fossil bone sufficiently well preserved for analysis. 

The isotopes, and give complementary information to this problem. The radiocarbon dating isotope with its nuclear half life of 5730 y, clearly allows to differentiate between fossil and biospheric feedstocks (98). 

Archaeologists, geologists, antiiropologists, and odier scientists take advantage of the presence of natural radioactivity in our environment to estimate the ages of fossils and artifacts with a technique called radiocarbon dating. For example, in... 

Half-Life and Radiocarbon Dating The half-life of a radioactive nuclide is the time it takes for half of the parent nuclides in a radioactive sample to decay. The presence of radioactive carbon-14 (with a half-life of 5730 years) in the environment provides a natural clock by which to estimate the age of many arfifacfs and fossils. All living things contain carbon-14. When they die, the carbon-14 decays with its characteristic half-life. A measurement of the amount of carbon-14 remaining in a fossil or are artifact can therefore reveal ifs age. 

Radiocarbon Dating Using Radioactivity to Measure the Age of Fossils and Artifacts... 

Radiocarbon (14C) dating is the most common application of AMS, and is also relevant for compound specific measurements. PAHs in sediments from an urban reservoir were 14C-free, but most of the PAHs in these sediments were derived from fossil fuel combustion rather than biomass burning.136... 

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