Age dating of environmental organic residues
There are three carbon isotopes that occur as part of the Earth's natural processes; these are carbon-12, carbon-13 and carbon-14.The unstable nature of carbon 14 (with a precise half-life that makes it easy to measure) means it is ideal as an absolute dating method.
Though their initial calculations were slightly incorrect thanks to the contaminants of extensive nuclear testing of the age, scientists soon discovered the error and developed methods that were more accurate, including a date of calibration to 1950.Radiocarbon dating may only be used on organic materials.Typically (6): The above list is not exhaustive; most organic material is suitable so long as it is of sufficient age and has not mineralised - dinosaur bones are out as they no longer have any carbon left.When an organism dies, it stops absorbing the radioactive isotope and immediately starts decaying (7).As previously mentioned, the half life of the C isotope is 5,730 years - this means that it takes 5,730 years to reach half the radioactivity that the organism had at the point of death, another 5,730 years to reach 25% radioactivity it had at the point of death and so on.AMS works slightly differently; it converts the atoms of the sample into fast-moving ions so that they become charged atoms.
By applying magnetic and electrical fields, the mass of these ions is measured and the accelerator is used to remove ions that might contaminate the dating.
The next big step in the radiocarbon dating method would be Accelerated Mass Spectrometry which was developed in the late 1980s and published its first results in 1994 (3).
This was a giant leap forward in that it offered far more accurate dates for a far smaller sample (9); this made destruction of samples a far less delicate issue to researchers, especially on artefacts such as The Shroud of Turin for which accurate dates were now possible without damaging a significant part of the artefact.
It also has some applications in geology; its importance in dating organic materials cannot be underestimated enough.
In 1979, Desmond Clark said of the method “we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation” (3).
Stone and metal cannot be dated but pottery may be dated through surviving residue such as food particles or paint that uses organic material (8).