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Given the short 14C half-life of 5730 years, organic materials purportedly older than 250,000 years, corresponding to 43.6 half-lives, should contain absolutely no detectable 14C. (One gram of modern carbon contains about 6 x 1010 14C atoms, and 43.6 half-lives should reduce that number by a factor of 7.3 x 10-14.) An astonishing discovery made over the past twenty years is that, almost without exception, when tested by highly sensitive accelerator mass spectrometer (AMS) methods, organic samples from every portion of the Phanerozoic record show detectable amounts of 14C! 14C/C ratios from all but the youngest Phanerozoic samples appear to be clustered in the range 0.1-0.5 pmc (percent modern carbon), regardless of geological ‘age.’
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Anomalous 14C in fossil material actually has been reported from the earliest days of radiocarbon dating. Whitelaw [46], for example, surveyed all the dates reported in the journal Radiocarbon up to 1970, and he commented that for all of the over 15,000 specimens reported, "All such matter is found datable within 50,000 years as published." The specimens included coal, oil, natural gas, and other allegedly ancient material. The reason these anomalies were not taken seriously is because the older beta-decay counting technique had difficulty distinguishing genuine low levels of 14C in the samples from background counts due to cosmic rays. The AMS method, besides its inherently greater sensitivity, does not have this complication of spurious counts due to cosmic rays. In retrospect, it is likely that many of the beta-counting analyses were indeed truly detecting intrinsic 14C.
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How do the various 14C laboratories around the world deal with the reality that they measure significant amounts of 14C, far above the detection threshold of their instruments, in samples that should be 14C dead according to the standard geological time scale? A good example can be found in a recent paper by Nadeau et al. [30] entitled, Carbonate 14C background: Does it have multiple personalities? The authors are with the Leibnitz Laboratory at Christian-Albrechts University in Kiel, Germany. Many of the samples they analyze are shells and foraminifera tests from sediment cores. It would very useful to them if they could extend the range for which they could date such biological carbonate material from roughly 40,000 years ago (according to their uniformitarian assumptions), corresponding to about 1 pmc, toward the 0.002 pmc limit of their AMS instrument, corresponding to about 90,000 years in terms of uniformitarian assumptions. The reason they are presently stuck at this 40,000-year barrier is that they consistently and reproducibly measure 14C levels approaching 1 pmc in shells and foraminifera from depths in the record where, according to the standard geological time scale, there should be no detectable 14C.
Their paper reports detailed studies they have carried out to attempt to understand the source of this 14C. They investigated shells from a late Pleistocene coring site in northwestern Germany dated by U/Th methods at 120,000 years. The mean 14C levels measured in the shells of six different species of mussels and snails varied from 0.1 to 0.5 pmc. In the case of one species, Spisula subtruncata, measurements were made on both the outside and inside of the shell of a single individual specimen. The average 14C value for the outside of the shell was 0.3 pmc, while for the inside it was 0.67. At face
value, this suggests the 14C/C ratio more than doubled during the lifetime of this organism. Most of their foraminifera were from a Pleistocene core from the tropical Atlantic off the northwest coast of Africa dated at 455,000 years. The foraminifera from this core showed a range of 14C values from 0.16 to 0.4 pmc with an average, taken over 115 separate measurements, of 0.23 pmc. A benthic species of foraminifera from another core, chosen because of its thick shell and smooth surface in the hope its ‘contamination’ would be lower, actually had a higher average 14C level of 0.58 pmc!
The authors then performed a number of experiments involving more aggressive pre-treatment of the samples to attempt to remove contamination. These included progressive stepwise acid hydrolization of the carbonate samples to CO2 gas and 14C measurement of each of four separate gas fractions. They found a detectable amount of surface contamination was present in the first fraction collected, but it was not large enough to make the result from the final gas fraction significantly different from the average value. They also leached samples in hydrochloric acid for two hours and cracked open the foraminifera shells to remove secondary carbonate from inside, but these procedures did not significantly alter the measured 14C values.
The authors summarize their findings in the abstract of their paper as follows, The resultsshow a species-specific contamination that reproduces over several individual shells and foraminifera from several sediment cores. Different cleaning attempts have proven ineffective, and even stronger measures such as progressive hydrolization or leaching of the samples prior to routine preparation, did not give any indication of the source of contamination. In their conclusion they state, The apparent ages of biogenic samples seem species related and can be reproduced measuring different individuals for larger shells or even different sediment cores for foraminifera. Although tests showed some surface contamination, it was not possible to reach lower 14C levels through cleaning, indicating the contamination to be intrinsic to the sample. They continue, So far, no theory explaining the results has survived all the tests. No connection between surface structure and apparent ages could be established.
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