Around that same time, governments began widespread atmospheric testing of nuclear weapons.
Libby, a Professor of Chemistry at the University of Chicago, predicted that a radioactive isotope of carbon, known as carbon-14, would be found to occur in nature.
The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere.
Plants take up c14 along with other carbon isotopes during photosynthesis in the proportions that occur in the atmosphere; animals acquire c14 by eating the plants (or other animals).
This is called “radiocarbon dating,” and it’s been used to determine the age of naturally occurring materials, like plants, rocks, and human remains, as well as things made from naturally occurring materials, including the Dead Sea Scrolls and the Shroud of Turin.
Radiocarbon dating was introduced in the 1940s, but it became workable, with standardized methods and widely adopted in the 1950s.