Radiocarbon age

Radiocarbon ages are reported in years "before present" (b.p.), which, by convention, refers to "before the year 1950 c.e."... 

Uncertainties, Limitations, and Complications in Radiocarbon Dating. Discrepancies between a measured radiocarbon age and the otherwise verified age of certain specimens are sometime found. These discrepancies are due to deviations from the basic assumptions on which the radiocarbon method rests, which are essentially, as follows ... 

The radiocarbon age from Equation (16.2) is expressed in years BP, i.e. Before Present, where Present, by convention, is 1950 AD. Actually, 1950 is considered the reference year in radiocarbon dating, especially due to historical reasons. Following the same convention, in Equation (16.2), when measuring 14/f(t), its value is usually normalized to the concentration of a standard material in 1950 the normalized value is expressed in units of pMC (per cent of Modem Carbon), the standard material being 100 pMC. 

It is well known that the radiocarbon age does not correspond to the real calendar age of an organism, since Equation (16.2) is based on assumptions that are true only to a first approximation namely, the hypothesis of a constant value of 14/f0 over time in the past. [ 10] An accurate calibration curve[ll,12] has thus to be used to convert the tRC value of a measured sample into its true age. For a complete discussion on this topic, the already cited literature on radiocarbon dating can be considered for reference. In contrast, the focus of this chapter is on how to measure the radiocarbon age tRC, i.e. how to measure uR(t). Assuming, as explained above, 14/f0 and t in Equation (16.2) are known, it is indeed clear that a measurement of 14/ (f) allows us to determine the radiocarbon age. 

In this way, it is possible to reach an extremely high selective sensitivity down to 1 part in 1015, which in 14C dating corresponds to being able to date samples about 50 000 years old. Moreover, modern systems can measure isotopic ratios in modern carbon, both C/ C and C/ C, with an ultimate precision as good as 2%o and l%o, respectively. The former value corresponds to determining the conventional radiocarbon age with an absolute error, smaller than in the past, better than 20 years, while the l%o precision for the 13C/12C allows an adequate correction for isotopic fractionation effects. Even in routine measurements, at least in the case of historical samples, a precision of 5%o in the 14C/12C measured value is standard, corresponding to an uncertainty in the radiocarbon age of 40 years.[27]... 

The case of Oetzi (or the Iceman), the frozen mummy found in 1991 on the Alps on the border between Austria and Italy and now kept at the Archaeological Museum of Bolzano (Italy), is also well known. AMS radiocarbon measurements from the laboratories of Zurich[78] and Oxford[79] on tissue and bone samples from the Iceman dated him to 4550 19 years BP. When calibrated, this radiocarbon age corresponds to three probable calendar time intervals between 3350 BC and 3100 BC. Consistent measurements were obtained by dating some of his equipment and also botanic remains from the discovery site. [80] In this context, it is important to note that dating of Oetzi represents a good example of the relevance of the behaviour of the calibration curve in the final precision of a radiocarbon measurement. Actually, in this case, despite a very high precision of the radiocarbon age ( 19 years), the special trend in the calibration curve around the dated period, i.e. in particular the so-called wiggles, prevents a more exact and unambiguous absolute age determination. 

Figure 16.6 Calibration of the radiocarbon ages of the Cortona and Santa Croce frocks the software used[83] is OxCal v.3.10. Radiocarbon age is represented on the y axis as a random variable normally distributed experimental error of radiocarbon age is taken as the sigma of the Gaussian distribution. Calibration of the radiocarbon agegivesa distribution of probability that can no longer be described by a well defined mathematical form it is displayed in the graph as a dark area on the x axis...

It is important to remember that sometimes, in spite of the excellent performances of an AMS measurement, the final uncertainty on the true calendar age of a sample is a function of the behaviour of the calibration curve in that time interval a small error on the radiocarbon age does not necessarily correspond to a small, or a unique, calendar span on the BC/AD axis. 

The measurement of both 14C and 12C is necessary to estimate the radiocarbon age on the basis of the isotopic ratio 14R measuring 13C allows us to evaluate the effects of isotopic fractionation, according to which the measured radiocarbon concentration can be corrected. For details, see Aitken.1... 

A.J.T. Jull, DJ. Donahue and P.E. Damon, Factors affecting the apparent radiocarbon age of textiles a comment on Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles the Shroud of Turin , by D.A. Kouznetsov et al., J. Archaeol. Sci. 23, 157 160 (1996) D.A. Kouznetsov, A.A. Ivanov and P.R. Veletsky, Effects of fires and biofractionation of carbon isotopes on results of radiocarbon dating of old textiles the Shroud of Turin, J. Archaeol Sci. 23, 109 121 (1996). 

Figure 27. Radiocarbon age vs. chronological age of tree rings vs. years 4000—...

Blake, Weston, Jr., Radiocarbon age determinations and postglacial emergence at Cape Storm, southern Ellesmere Island, Arctic Canada, Geografiska Annaler, 57, Ser. A, 1-2, 1-71 (1975). 

Bada, J.L., Gillespie, R., Gowlett, J.A.J. and Hedges, R.E.M. (1984). Accelerator mass spectrometry radiocarbon ages of amino acid extracts from Californian Palaeoindian skeletons. Nature 312 442 144. 

Figure 10.4 Carbon isotope ratios in bone collagen plotted against radiocarbon ages for British Mesolithic and Neolithic humans. (Reprinted by permission from Macmillan Publishers Ltd Richards et al., 2003. Copyright 2003.)...

Figure 8.10 Carbon isotope ratios in bone collagen plotted against radiocarbon ages for 183 British Mesolithic and Neolithic humans from coastal (within 10 km of modern coastline squares) and inland sites (crosses). The sharp change in carbon isotope ratio at around 5200 radiocarbon years BP is interpreted as a shift from a marine diet to one dominated by terrestrial protein. This coincides with the onset of the Neolithic period in Britain. (Reproduced from Richards et al. 2003, with permission of Nature Publishing Group and the first author.)...

Broecker, W.S., M. Klas, E. Clark, G. Bonani, S. Ivey, and W. Wolfli. 1991. The influence of CaCOn dissolution on core top radiocarbon ages for deep-sea sediments. Paleoceanography 6(5) 593-608. 

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