Willard Libby: A Man For the Ages

Lying about your age got a whole lot harder thanks to the man who was born this week (Dec. 17) in 1908. Willard Libby was a chemist who had worked on the atomic bomb during WW II, but his real claim to fame (relatively speaking) came from his pioneer work in the scientific method of “radiocarbon dating.”  Today we use radiocarbon dating to determine the ages of everything from ancient Egyptian mummies to the Dead Sea Scrolls.  It has proven to be so accurate that it can identify within a few years the ages of objects up to 70,000 years old.

Libby’s forays into radiocarbon dating began at the University of Chicago in 1947, where he conducted experiments on carbon-14, the carbon isotope on which radiocarbon dating is based.  Libby’s experiments were predicated on several known facts, beginning with the fact that carbon-14 is produced when nitrogen is bombarded by cosmic rays in the atmosphere.  It then falls to Earth where it becomes carbon dioxide, which — as we know from our high school biology days — is then absorbed by plants through “photosynthesis.”  From there, carbon spreads to the animals, such as humans, that eat the plants, and to the other animals (humans included) that eat the animals that eat the plants.

The point, as Libby surmised, is that everything containing carbon, including living organisms, also contains various levels of carbon-14. Or to put it another way, we are all slightly radioactive.  What’s more, when an organism dies it stops absorbing carbon-14, and instead starts losing it as part of the decaying process.  Because carbon-14 decays at a predictable rate — one-half of the original amount disintegrates every 5,700 years — Libby concluded that if there was a way to measure how much carbon-14 had been lost, and how much was left in an organism, then one could accurately predict how old that organism was.  Using a sophisticated Geiger counter to measure carbon-14 amounts, and a sophisticated scientific formula that is too complicated for me to understand, let alone explain, Libby then tested his radioactive carbon dating method against pieces of wood (once part of a living tree) from an Egyptian tomb whose age was already known.  They matched, and radiocarbon dating would subsequently revolutionize such fields as archeology, anthropology and geology.  It would also, not surprisingly, spark new debates over religion.

One of those unknown “Men of Science” whose work has profoundly affected modern life and human understanding, Libby received the 1960 Nobel Prize for Chemistry.  He died quietly in 1980, and ironically — or perhaps intentionally — Libby ensured that scientists from 70,000 years in the future would never be able to determine his age. He was cremated and his ashes scattered.