Carbon-14 or “radiocarbon” dating can be used to judge the approximate age of potentially ancient materials.
Carbon-14 dating is a process by which scientists or archaeologists might measure the ‘age’ of a piece of organic matter, or its date of death, to be more specific, by comparing the number of carbon-14 isotopes in the sample to the number of carbon-12 isotopes.
Carbon exists in three varieties, carbon-12, which makes up a little less than 99% of the world’s carbon, carbon-13, which makes up about 1% of the world’s carbon, and carbon-14, which makes up something in the realm of .0000000001% of the world’s natural carbon. Isotopes of an element are the same in every way chemically, but contain a different number of neutrons, or neutral atomic particles in their nucleus. This gives them often-differing atomic properties. Carbon-14, for instance, is radioactive, with a half-life of 5568 years. This means that every 5568 years, 100g of theoretical carbon-14 will have degenerated into 50g of the same material. Scientists can therefore use this property of the isotope to gauge the relative date of the material in question.
In order to get an accurate concept of the date of a sample, three items must be tested:
- The “X”.
- A geologic “baseline” sample.
- A standard.
The “X”, of course, is your sample, the undetermined factor to be tested. The geologic sample is an ancient piece of carbon, any piece, really, that can be used to determine the amount of variation to be expected in any sample, sometimes called “background activity”. When the final answer is determined, this amount is subtracted from the other measurements to ensure accuracy.
The standard is a modern sample, most often one of three mass-produced ‘standards’ created in 1955 and 1977 or a personal laboratory standard. Any standard consists of a large supply of organic material, often oxalic acid from beet crops, which was produced in the same year and so has a mostly uniform level of decay. The date of the sample’s production becomes the date by which the final measurement is taken.
In summary, the ratio of carbon-14 to carbon-12 is gathered from a test sample (X), a geologic sample (A), and a modern sample (B). You subtract A’s ratio from B (since A is the baseline), then subtract A from X, and then compare your new X to your new B. This isn’t a precise scientific formula, of course, but it should give you a good idea of the principles involved.
Because of the relatively short half-life of carbon-14 its effective range is generally less than 50,000 years, so anything older than that must be tested using other, often less appropriate methods of dating. Carbon-14 dating can, however, therefore be applied to most historical and archaeological study today.
Ideal materials include:
- Bone, hair, shells and other animal or human matter.
- Wood, pollen, seeds and preserved plant matter.
- Manufactured goods such as cloth textiles.
Non-organic materials may also be tested (somewhat less reliably) through the process of associating their age with the age of materials discovered in the same stratum of a dig site. For instance, a stone tool could not effectively be tested for its materials were never alive, but trace amounts of pollen on the tool or wood found near it could be dated rather easily, lending archaeologists a clue to its origins. Pottery, as well, may sometimes be carbon-dated if it contains fragments of organic matter or can be associated with nearby datable objects.