Once an organism dies the carbon is no longer replaced.
Because the radiocarbon is radioactive, it will slowly decay away.
Radiocarbon dating is one of the most widely used scientific dating methods in archaeology and environmental science.
It can be applied to most organic materials and spans dates from a few hundred years ago right back to about 50,000 years ago - about when modern humans were first entering Europe.
The dating process is always designed to try to extract the carbon from a sample which is most representative of the original organism.