Alternatives radio carbon dating
This database originated in a printed index compiled by Cherry Lavell and produced by the Council for British Archaeology in 1971, with four later printed supplements to 1982.
The radiocarbon determinations were gathered and collated by hand from all available sources (the journal Radiocarbon plus the entire range of UK and Irish archaeological publications, both national and more local) to produce the most accurate and complete description possible for each published date.
The database should therefore be regarded as somewhat provisional, and the given references checked, because they will nearly always give more details about the sample to assist in assessing both its context and its validity.
The Holocene part of the calibration curve is derived from radiocarbon analyses of tree-rings of known age.
Corals and other materials are used for the late-Pleistocene section.
No reviewer recommended accepting the paper, until an “eminent” statistician was asked to review the paper and declared the paper to be “obviously correct”. Without explaining the traditional method of calibrating dates, Keenan proposes an alternative procedure that gives very different results, as shown by calibrating 4530 ± 50 The shape of the probability distribution function is very different from that calculated by Ox Cal above. Replacing R with the calibration curve g(T), P(R) is defined as To obtain P(T), the probability distribution along the calendar year axis, the P(R) function is transformed to calendar year dependency by determining g(T) for each calendar year and transferring the corresponding probability portion of the distribution to the T axis.
Yes, I know that’s difficult to grasp, but it is actually very easy to implement, even in Excel (but don’t bother). Starting with 5600 BP, the calibration curve at this calendar date is ~4800 C BP is low. The procedure is then repeated every year (or five years) along the time axis to get the probability density for each year.
But it makes the implicit assumption that the every radiocarbon date is equally likely.
It is easy to demonstrate that this is not true by taking the calibration curve and for each calendar date, finding the probability of each radiocarbon age. The probabilities assigned for each radiocarbon age are then summed. By inspecting the calibration curve, it is obvious that peaks in summed probability coincide with plateaux in the radiocarbon calibration curve.
With the date 4530 ± 50 C BP, the peak of the radiocarbon date’s Gaussian distribution is close to the calibration curve between ~53 BP, so all these dates are assigned a high probability.
So although the radiocarbon date has a Gaussian distribution, the effect of this procedure is to weight parts of that distribution that are close to a plateau more heavily than parts of the distribution where the calibration curve is steep. Keenan wants the Gaussian distribution to be preserved.
Apart from a number of determinations that were poorly (incompletely) published, the list was comprehensive up to 1982; but thereafter the flow of dates from laboratories became too rapid for a part-time editor to collect and process, and in 1986 the collection process virtually ceased.