Radiocarbon dating sample problems

Most information on the past 30,000 years or so is from sites or specimens that have been dated using radiocarbon (14C).However, the radiocarbon age scale that would be calculated from first principles (based on the decay rate of the 14C isotope, assuming that 14C was at the same level of abundance as it is at present) is not always reliable, because there have been fluctuations in the rate of production in 14C at the top of the atmosphere.At the extremes there is a range from 10,447 to 11,700 year B. And evidence that properly conducted C14 radiometric dating can approach reasonable accuracy, possibly within better than 10 percent.

Figure 2 shows an atmospheric 14C calibration for the complete 14C dating range (less than 45 ka). Atmospheric radiocarbon calibration for almost the complete 14C dating range (less than 45 ka cal BP) reconstructed from annually laiminated sediments from Lake Suigetsu (Japan).

The sedimentation or annual varve thickness is relatively uniform, typically 1.2 mm per yr for present conditions in Lake Suigetsu which is located near the coast of the Sea of Japan.

Recently scientists took a 75-m long continuous core from the center of the lake for close analysis including AMS 14C measurements on more than 250 terrestrial macrofossil samples of the annual laminated sediments.

The problems are particularly great at about 10,000 14C y.a., when a large influx of 14C-depleted carbon from the oceans, combined with a decrease in the rate of 14C production at the top of the atmosphere, gives an 'age plateau' such that the same 14C age covers a wide span of real time, about 1,000 years. U/Th) can be used to attempt to check the 'true' age of specimens or sediment layers dated by 14C, although these all have substantial error margins of their own.

The most convincing way to check the 14C age scale is through biological or sedimentological features which build up annual layers over long periods of time (e.g.

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= Lake Suigetsu (Japan); o = Lake Gosciaz (Poland).

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