(Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.) Land plants, such as trees, get their carbon from carbon dioxide in the air. The same is true of any creature that gets its carbon by eating such plants. Suppose such a creature dies, and the body is preserved.The C14 will undergo radioactive decay, and after 5730 years, half of it will be gone. So, if we find such a body, the amount of C14 in it will tell us how long ago it was alive. The method doesn't work on things which didn't get their carbon from the air.This leaves out aquatic creatures, since their carbon might (for example) come from dissolved carbonate rock.
The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. It is found in the air in carbon dioxide molecules.
It was developed right after World War II by Willard F.
Libby and coworkers, and it has provided a way to determine the ages of different materials in archeology, geology, geophysics, and other branches of science.
Carbon-14 decays to nitrogen-14 by emitting an electron and a neutrino, and it does so with a half-life of 5,730 years.
Thus, if one started with 1,024 atoms of carbon-14, after 5,730 years, only 512 would remain.All life requires carbon and, chemically speaking, carbon-14 acts just like the far-more-abundant carbon-12.