All organisms have a certain amount of 14C present in their bodies – it is absorbed out of the atmosphere by plants during the process of photosynthesis, and transferred to animals when the plants are eaten.While alive, organisms experience a balance of 14C intake and dissipation.
The levels of 14C present in a specimen can be measured in a variety of ways; however the invention of accelerator-based mass spectrometric techniques have drastically increased measurement accuracy, as it provides a count of the number of 14C atoms present in a sample.
It has been used to date specimens up to 60,000 years in age.
Radiocarbon dating is essentially a method designed to measure residual radioactivity.
By knowing how much carbon 14 is left in a sample, the age of the organism when it died can be known.
Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes.