Brief history carbon dating
When a plant or animal dies it stops taking in carbon-14 and radioactive decay begins to decrease the amount of carbon-14 in the tissues.
The age of the plant or animal specimen containing carbon, such as wood, bones, plant remains, is determined by measuring the ratio of carbon-12 to carbon-14. Because of this relatively short half-life, carbon-14 can only be used to date specimens up to about 45,000 years old.
After this the amount of carbon-14 present in the sample is too small to be measured precisely.
Carbon-14 can not be used to measure the age of very young specimens as the difference between the amount of carbon-12 and carbon-14 will not be sufficient to be detected.
Carbon-14 dating relies on the following assumptions: It is known that the radiocarbon content of the atmosphere has varied in the past, so the initial activity of carbon-14 has NOT been a constant.
The following variations in carbon-14 activity have been noted: Calibration curves have been produced by comparing radiocarbon dates with other dating methods such as dendrochronology (a dating method using the tree's growth rings).
This allows corrections to be made on radiocarbon dates in order to produce more accurate dates.
It should be noted that it is not the artefact that is being dated, it is the soot, ash or charring.
Carbon-14 is continually formed in nature by the interaction of neutrons with nitrogen-14 in the Earth’s atmosphere; the neutrons required for this reaction are produced by cosmic rays interacting with the atmosphere.
Radiocarbon present in molecules of atmospheric carbon dioxide enters the biological carbon cycle: it is absorbed from the air by green plants and then passed on to animals through the food chain.
Radiocarbon decays slowly in a living organism, and the amount lost is continually replenished as long as the organism takes in air or food.
Once the organism dies, however, it ceases to absorb carbon-14, so that the amount of the radiocarbon in its tissues steadily decreases.
Carbon-14 has a half-life of 5,730 ± 40 years—, half the amount of the radioisotope present at any given time will undergo spontaneous disintegration during the succeeding 5,730 years.