Facts carbon 14 dating
For example, if a sample emits radiation indicating the presence of 10 carbon-14 atoms and we know from its mass that it originally must have contained 20, that means the plant or animal from which the sample was taken died about 5,730 years ago.
Carbon-14, along with the more common, stable (nonradioactive) carbon isotopes carbon-12 and carbon-13, combine with oxygen to produce carbon dioxide.
Animals, in turn, eat the plants (or eat other animals that have eaten the plants), and thus the carbon-14 atoms propagate throughout the food chain.
The result is that everything that is alive, or once was, contains some number of carbon-14 atoms.
Likewise, the proportion of carbon-14 to carbon-12 in the environment must have remained fairly constant.
And in any given sample, one must be certain that contaminants from other time periods are not present—a sometimes-tricky issue.
As is often the case, the controversy over this topic is at least as interesting as the topic itself.