Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Willard Frank Libby (1908-1980) won the 1960 Nobel prize in chemistry for discovering a technique for dating objects of biological origin and used in archaeology and other sciences by measuring the decay of radioactive carbon 14 which they contain. This isotope is continually being created by gamma radiation of nitrogen in the upper atmosphere, and it decays with a half-life of 5700 years. A tiny fraction of the carbon in the atmosphere, it quickly forms carbon dioxide and is equally assimilated by living organisms such as trees. However, when an organism dies, its exchange of carbon dioxide with the atmosphere ceases, and the fraction of carbon 14 in its molecular structure starts to decrease. The time period from its death can then be calculated from the carbon decay in comparison to that of a living specimen. Unlike many other Nobel prize winning discoveries, this one is simple to grasp and yet is a powerful tool in verifying age of natural remains. The stamp shows the exponential decay curve of carbon 14, an archaeological dig, and the head of a mummy.