Number 14 of the process carbon 14 dating
A detailed description of radiocarbon dating is available at the Wikipedia radiocarbon dating web page.
Bottom line: Radiocarbon dating is a technique used by scientists to learn the ages of biological specimens from the distant past.
Carbon-14 dating can be used on objects ranging from a few hundred years old to 50,000 years old.
Libby and others (University of Chicago) devised a method of estimating the age of organic material based on the decay rate of carbon-14.
Here’s an example using the simplest atom, hydrogen. Carbon-14 is an unstable isotope of carbon that will eventually decay at a known rate to become carbon-12.
But when gas exchange is stopped, be it in a particular part of the body like in deposits in bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease.
If you ever wondered why nuclear tests are now performed underground, this is why.
Most radiocarbon dating today is done using an accelerator mass spectrometer, an instrument that directly counts the numbers of carbon-14 and carbon-12 in a sample.
It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes and human activities.
Among the significant events that caused a temporary but significant spike in the atmospheric carbon-14 to carbon-12 ratio were above-ground nuclear test detonations in the two decades following World War II.
For example, plastic, stones, plants, animals and so on.