For radiocarbon dating to be reliable scientists need to make a number of vital assumptions.Firstly, Dr Libby assumed that C14 decays at a constant rate.A petrified miner’s hat and wooden fence posts were unearthed from an abandoned 19th century gold hunter’s town in Australia’s outback.
However, experimental evidence indicates that C14 decay is slowing down and that millennia ago it decayed much faster than is observed today.
Secondly, the theory behind C14 dating demands that there is the same rate of cosmic production of radioactive isotopes throughout time.
The industrial revolution has belched hundreds of thousands of tons of carbon gases into the atmosphere increasing the C12 ratio and atomic weapons testing have increased neutron levels.
Thirdly, the environment in which the artefact lies heavily impacts on the rate of decay.
The most important archaeological dating method is radiocarbon dating.
It is a technique that can yield absolute dates with accuracy up to approximately 5000 years before present.
As with any radioactive particle it decays over time. Libby in 1948 at the University of Chicago, showed that C14, tested in his laboratory, decayed at the rate that, projected out, would cause half of its weight to be lost in 5568 years.
Hence, the term ‘half-life’ was given to radioactive substances.
Some examples of abnormal C14 results include testing of recently harvested, live mollusc shells from the Hawaiian coast that showed that they had died 2000 years ago and snail shells just killed in Nevada, USA, dated in at 27,000 years old.