Why carbon dating works
The radiocarbon half-life or decay rate has been determined at 5,730 years.
Chemists have already determined how many atoms are in a given mass of each element, such as carbon.4 So if we weigh a lump of carbon, we can calculate how many carbon atoms are in it.The reason is that, as long as the organism is alive, it replaces any carbon molecule that has decayed into nitrogen.After plants and animals perish, however, they no longer replace molecules damaged by radiocarbon decay.The standard way of expressing the decay rate is called the half-life.5 It’s defined as the time it takes half a given quantity of a radioactive element to decay.
So if we started with 2 million atoms of carbon-14 in our measured quantity of carbon, then the half-life of radiocarbon would be the time it takes for half, or 1 million, of those atoms to decay.
If carbon-14 has formed at a constant rate for a very long time and continually mixed into the biosphere, then the level of carbon-14 in the atmosphere should remain constant.