Wednesday, June 17, 2015

Digging Up the Root of Carbon Dating

The discovery of the principle behind carbon dating was reported in The New York Times two years before its remarkable implications were widely understood.

On Dec. 28, 1947, in a roundup of the year’s events in atomic physics, Waldemar Kaempffert wrote that “Prof. Willard F. Libby and his colleagues discovered that radioactive carbon 14 is produced by cosmic rays and that there is enough of it in all living matter to constitute one of the most important sources of radiation to which the human body is exposed.”

Two years later, the importance of the discovery had become clear. “Scientist Stumbles Upon Method to Fix Age of Earth’s Material” read the headline of an unsigned article on Page 29 of The Times on Sept. 6, 1949, marking the first time that readers learned of radiocarbon dating.

The article said that Dr. Libby, a 40-year-old chemistry professor at the University of Chicago, “stumbled on the technique two years ago when studying cosmic ray action on the atmosphere.” Then it offered a brief explanation of the method, saying that living materials contain radioactive carbon that decays after death at a known rate, and that this rate can be used to determine with great accuracy when a plant or animal died.

“We have reason to believe that ages up to 15,000 to 20,000 years can be measured with some accuracy,” Dr. Libby told The Times.

On Dec. 31, 1951, the newspaper reported that J. Laurence Kulp hadimproved the technique, so that it could be used to date materials as old as 30,000 years. Two years later, The Times reported that Canadian researchers were able to extend the range to 40,000 years with “liquid scintillation,” still used to test the radioactivity of low-energy isotopes.

Through the 1950s, The Times reported on the use of radiocarbon dating to discover the age of the Pyramid of the Sun in Mexico, the wood in a 4,600-year-old Egyptian coffin, sandals found in a cave in Oregon and the wooden floor of an ancient Syrian palace. Today, the technique continues to be refined, and dates of prehistoric objects and events are sometimes modified. As recently as last summer, Kenneth Chang reported that the newest techniques and equipment had been used to revise the dates of the period that Neanderthals and modern humans lived together in Europe.

But all of this depends on the principle that Dr. Libby was the first to elucidate, and his contribution did not go unnoticed. As The Times reported on Nov. 6, 1960, Dr. Libby was awarded the Nobel Prize in Chemistry. The Nobel Committee cited him “for his method to use carbon 14 for age determination in archaeology, geology, geophysics and other branches of science.”

Bakalar, Nicholas. 2015. “Digging Up the Root of Carbon Dating”. The New York Times. Posted: April 20, 2015. Available online:

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