Why is the use of carbon-14 limited

Carbon-14 is naturally created with the interaction of high-energy cosmic rays with atmospheric nitrogen. As part of the atmosphere, living organisms take in the carbon and incorporate this into living tissues. As long as the organism is alive and breathing, it keeps adding new carbon-14. When the organism dies, it stops gaining carbon-14 - or anything else, of course.

Carbon-14 is slightly radioactive, with a half-life of about 5700 years. If we assume that the atmospheric production of carbon-14 has been steady for the last 100,000 years, we can calculate the approximate age of when the organism died by determining what percentage of carbon-14 still exists in the dead material.

Paleo-archaeologists and anthropologists use this information when studying old cultures and civilizations.