This leaves the amount in the air relatively constant.
Radiocarbon immediately reacts with oxygen in the air to form carbon dioxide (CO2).
Although carbon-14 is radioactively decaying away in the body, it is constantly being replaced by new photosynthesis or the ingestion of food, leaving the amount relatively constant.
When a plant stops assimilating carbon dioxide or when an animal or human being stops eating, the ingestion of carbon-14 also stops and the equilibrium is disrupted.
It also means that if a dead plant has 50% as much carbon-14 in it than in a living plant, the dead plant was alive about 5,700 years ago.
After 50,000 years, a fossil won’t have any radiocarbon left in it.
Carbon-14 will have all disappeared by radioactive decay.