Firstly the technique reaches its limit about 40,000 to 50,000 years (www.1) as the total amount of 14C has reduced by so many half-life's that it becomes difficult to date. Another problem is that contamination of older samples by younger carbon, this contamination causes the material to seem younger then it actually is (Geyh and Scleider, 1990). Finally there is an effect known as the Suess effect' that was first noticed by Suess. He found that due to the increase input of carbon into the atmosphere from industrialisation, the dates of the materials could be found to be inaccurate (www.3). The increased input of carbon led to a change in the ratios of the three carbon isotopes in the atmosphere and therefore in the biosphere. This means .
that the dates of the materials sometimes appear older then they actually are but this only occurs when dating samples from the 20th Century as this is when the ratios of carbon have been dramatically changed (www.3).
The advantages of this method are that it can be used on anything that was once living as they all contain carbon.
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Luminescence Dating.
This method is also used to date loess, which was developed in the 1960's (www.4). It is based on the fact that many minerals, such as quartz and feldspars, are able to act as dosimeters that record the amount of ionising radiation they are exposed to (www.4). The energy created by this ionising radiation is stored within the crystal structure (Duller, 2002). The radiation is from Uranium, Thorium and potassium found in the sediments surrounding the sample (www.4). When this sample is exposed to heat or light it emits light that is known as luminescence. When the sediment is being transported and is exposed to daylight the luminescence signal is zeroed which means that as the material is buried the signal begins to increase over time. It is this signal that is measured. This mean it is essential when the sample is taken not to expose it to daylight and therefore causing the signal to return to zero again.
