Limitations of radiocarbon dating
This discovery meant that there are three naturally occurring isotopes of carbon: Whereas carbon-12 and carbon-13 are stable isotopes, carbon-14 is unstable or radioactive.
Libby received the Nobel Prize in Chemistry for his work in 1960.
Prior to the development of radiocarbon dating, it was difficult to tell when an archaeological artifact came from.
Unless something was obviously attributable to a specific year -- say a dated coin or known piece of artwork -- then whoever discovered it had to do quite a bit of guesstimating to get a proper age for the item.
Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.
In contrast, methane made from petroleum products had no measurable radioactivity.
Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).