In 1947 Willard Frank Libby found out the method of radiocarbon dating for establishing the age of an enormous diversity of organic materials from bone to wood to fabric. More recently, accelerator mass spectrometry has extended the range of the technique, confirming it as an indispensable tool in geology, anthropology, archaeology and paleontology.
Only small samples are now required to date invaluable items such as the famous Turin shroud. Radiocarbon analysis of the shroud in 1988 revealed that the flax it is made of was harvested around AD 1325 (plus or minus 33 years), proving the relic to be medieval and not Christ’s winding sheet as was commonly believed.
Libby, an American chemist, joined the Manhattan Project during the Second World War where he worked on the separation of uranium isotopes for the development of the atomic bomb. After the war he moved to the Institute of Nuclear Studies at the University of Chicago and soon realized that radioactive carbon, or carbon-14, could be used to dale organic materials, a discovery that earned him the Nobel Prize for Chemistry in 1960.
In 1939 it was shown that carbon-14 is formed by the action of cosmic rays on atmospheric nitrogen. So carbon dioxide containing traces of this isotope is continually being incorporated into all living organisms and indeed all organic products derived from them After death, no more carbon-14 is incorporated, and what remains begins its natural decay to the stable isotope carbon-12. As the rate of decay is known, measurement of the new ratio of the two forms of carbon establishes the time elapsed since death. But at 5,730 years, the half-life of radiocarbon is relatively short so the method is used mainly to date materials