The approximate time since the organism died can be worked out by measuring the amount of carbon-14 left in its remains compared to the amount in living organisms.
A small but representative fraction have now been radiocarbon dated at three different AMS laboratories.
The present paper summarizes the results of these measurements (see also Rom etal., 1999).
This paper summarizes radiocarbon measurements of mainly botanical samples from the Iceman ("Otzi") and from his discovery site, an Alpine glacier at the Austrian-Italian border.
Materials that originally came from living things, such as wood and natural fibres, can be dated by measuring the amount of carbon-14 they contain.
For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain.
Later called Ötzi the Iceman, small samples from his body were carbon dated by scientists.
The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. It is found in the air in carbon dioxide molecules.
The amount of carbon-14 in the air has stayed the same for thousands of years.
There is a small amount of radioactive carbon-14 in all living organisms because it enters the food chain.
Once an organism dies, it stops taking in carbon-14.
The carbon-14 it contained at the time of death decays over a long period of time, and the radioactivity of the material decreases.