Organic material, radiocarbon dating

Radiocarbon dating relies on the fact that carbon exists naturally in several isotopic forms. All of them are virtually identical chemically, but they can be distinguished with special methods of analysis. One isotope, carbon-14, provides a kind of elemental clock that reveals the age of carbon-rich materials from living organisms. This technique is one of the most valuable of the many uses that chemists, geologists, medical biologists, and other scientists have found for isotopes the sibling forms that every element displays. 

Fractionation and Contamination. The ratio 14C/12C in certain materials may be affected by isotopic fractionation. For example, the uptake of carbon dioxide and its incorporation into plant tissue may be accompanied by substantial fractionation that depends on the plant species. With marine organisms, fractionation may also be important, especially when inorganic carbonate and bicarbonate are involved. Corrections for fractionation must be made for precise radiocarbon dating. 

The Trolinger bog sample is another example which shows the presence of these non-collagen organic materials in both fractions, although they are more abundant in the HCl-soluble fraction. These organic materials could possibly aflFect the radiocarbon date. However, there is no other date for comparison except that of an older peat unit in which the mastodon was buried. 

Radiocarbon dating is a technique used widely by archaeologists to date articles composed of organic material (e.g. wood), and the importance of the method was recognized in 1960 by the award of the Nobel Prize in Chemistry to its developer, W.F. Libby. The method relies on the fact that one isotope of carbon, gC, is radioactive (n = 5730 yr) and decays according to equation 2.34. 

For example, continuous vertical mixing of the ocean provides the surface waters with some abyssal Die that has been removed from contact with atmospheric CO2 for up to 1500 years. This process gives the ocean an average surface water reservoir age of about 400 years (A " C= —50 ppt). A constant correction factor of 400 years often is subtracted from the radiocarbon dates of marine materials (both organic and inorganic). There are regional differences, however, and in upwelling areas the true deviation can approach 1300 years. 

Figure 24.12 Using the radiocarbon dating method on organic materials, such as ash and charcoal found at the Great Pyramid of Giza, scientists estimate the pyramid to be more than 4000 years old. 

Radiocarbon dating is a technique used widely by archaeologists to date articles composed of organic material (e.g. wood), and the importance of the method was recognized... 

Although in theory it is possible to date the death of any living organism by radiocarbon, there are a number of practical limitations on the materials that can be meaningfully analyzed. Firstly, as with all dating techniques, there is the question of sheer durability it is only possible to date those materials that have survived from antiquity. These seldom include soft tissue, or the more transitory plant fibers, and even given the extended range of sample types... 

Radiocarbon Dating Method of absolute dating based on the radioactive decay of carbon in organic materials. 

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