There are three principal isotopes of carbon that are naturally occurring, 12C, 13C and 14C, the latter being radioactive and used in this dating method. This method is based on the rate at which 14C decays. Plants and animals take up carbon throughout their lifetime and during this time the 14C is stored within their bodies. When they die they no longer absorb carbon but instead the carbon begins to decay. By measuring the amount of decaying carbon relative to the other forms of carbon, it is possible to calculate back to the time of death of the organism being dated (www.2). The measurement of 14C can be measured in two ways, by counting the number of beta particles being emitted or by Accelerator-mass spectrometry age determination. This involves the direct measurement of 14C atoms, which is achieved by passing charged particles through a magnetic field at high speeds (Mannion, 1999). .
This dating method can be applied to loess by dating the organic matter contained within the palaeosols, which are old soils formed at the earth's surface (Duller, 2002). By dating the palaeosols, the loess that is found above and below the soil can be dated roughly. This method was carried out by Martin (1993) in the Central Great Plains of USA. Here the age of the loess was established using radiocarbon dating of humates extracted from two layers of palaeosols called the Gilman Canyon Formation and the Brady Palaeosol. Following experiments Martin established that:.
Gilman Canyon Formation at base - 35,000 BP.
Near the top - 20,000 BP.
Brady Palaeosol - 11,800 - 8800 BP.
A layer of loess found in this area called the Peoria loess that is located above the Gilman Canyon Formation and below the Brady Palaeosol. This investigation concluded that the Peoria loess appeared to have been deposited between approximately 20,000 and 10,500 BP. .
There are however a number of problems associated with this method of dating.