Radiocarbon Dating was developed by a team led by Willard F. Libby just after World War II and won him a Nobel Prize for the work. It is based on the fact that when organisms die the amount of Carbon-14 in the remains decay at a fixed rate. Although initially hailed as a definitive dating method for organic remains, it soon became obvious that it was not as reliable a tool as initially thought.
Originally a Carbon-14 half-life of 5568±30 years was used and is known as the Libby half-life. Later this was revised to 5730±40 years and is known as the Cambridge half-life. The initial theory was based on the assumption that Carbon-14 was being produced at a constant rate. However, this constancy has been questioned, as it can vary as a result of changes in the earth’s magnetic field. The intervention of man in the form of atomic bomb tests briefly doubled the amount of Carbon-14 produced. Local events can also have a dramatic effect on measurements; for example, the Tunguska explosion left the soil there so enriched with Carbon-14 that it gives a date in the future (1). Emilio Spedicato has also pointed out that Carbon-14 can be created in the atmosphere by any cometary or asteroidal impact and so alter the assumed constant ratio of C12 to C14.
Graham Phillips mentions[034] that ‘recent evidence suggests that that the level of Carbon 14 in the atmosphere may have decreased permanently around 3,500 years ago due to changes in the earth’s magnetic field.’ This has resulted in dates around that period being up to 500 year out. Calibration figures are now available to take account of some of these deviations based on data from dendrochronology, ice and sediment cores and coral samples. Further refinements are not to be ruled out.
Radiocarbon dating is only useful up to a maximum of around 50,000 years. In February 2010, researchers at Queens University Belfast announced a new calibration curve that extends back over the 50 millennia. The producton of this calibration curve is the result of 30 years research into the variations in athmospheric Carbon 14 caused by solar activity, the earth’s magnetic field and the oceans. Other radiometric dating methods are now available to deal with dates beyond this limit.
2010 also saw another important refinement of radiocarbon dating with the development of a ‘non-destructive carbon dating’ method which will enable the dating of very delicate, rare or highly valuable artefacts, without having to destroy any samples from them, as is required at present(a).
One strong dissenting voice was that of archaeologist, Zahi Hawass, Secretary General of the Egyptian Supreme Council of Antiquities who said “Carbon-14 dating has a margin of error of 100 years. In order to date Egyptian dynasties, we need to have specific dates; you cannot use carbon dating,” Hawass explained to Al-Masry Al-Youm. “This technique shouldn’t be used at all in making changes to the chronology of the ancient Egypt, not even as a helpful addition.”(b).
One of these, namely, the potassium/argon method has been claimed by writers such as Richard Milton[521] to have its own inherent problems and must be treated with caution. It appears that although dating methods have advanced greatly further improvements can be expected.
(1) New Scientist (7/9/02, p.14)
