Originally printed in the Jan. 8, 2003 edition of the Illinois Valley News
All matter is made of atoms, according to modern scientists. Atoms are made of a nucleus, and electrons which move around that nucleus. The nucleus is made mostly of protons and neutrons with many other particles which have been identified and named. In a stable nucleus the proton number is the same as the number of electrons while the neutron number can be varied. However, if the number of neutron gets too large or too small, the nucleus becomes unstable. In order to gain stability, the nucleus releases energy and pieces of matter, this is the source of radioactivity and is called radioactive decay. Most is harmless to living things, but it can be measured with Geiger counters.
In the atmosphere there are many nitrogen atoms and occasionally a cosmic ray from space will change a nitrogen nucleus into an unstable carbon-14 nucleus. Normal carbon is carbon-12 and carbon-14 changes to carbon-12 by radioactivity. The carbon-14 atom will still react with oxygen to produce carbon dioxide which in turn will react normally. The amount of radioactive carbon dioxide is very small but is measurable and maintains a fairly constant percentage of the total carbon dioxide in the atmosphere. This carbon dioxide is picked up by plants during photosynthesis and all animals get a constant percentage by eating the plants or eating other animals which eat plants. The percentage of carbon-14 in the body of a plant or animal remains constant until they die, then the carbon-14 percentage begins to drop as it changes to carbon-12.
In 1947 Willard Libby first proposed his theory concerning the process of using carbon-14 to measure the age of ancient or prehistoric life. His procedure is based on some built- in, unprovable, assumptions, but it has been tested on materials which have known ages and has proven reliable. The percentage of carbon-14 in the atmosphere, and in living organisms, is measurable for the present time. The rate by which carbon-14 decays to carbon-12 is also fairly constant and is able to be calculated mathematically. The assumptions are: 1. That the amount of carbon-14 in the atmosphere of past ages is the same as now. 2. That the rate of radioactive decay has remained relatively constant during the intervening time. The process of determining the age of an object, is simply measure the percentage of carbon-14 present in the specimen, then compare this to the percentage in a similar material of today. This will show how much carbon-14 has changed to carbon-12, and consequently how much time was required to make that change. It is considered only reliable up to 60 thousand years.
Willard Frank Libby received the Noble Prize for Chemistry in 1960 for his discovery and testing of this process. He was born Dec. 17, 1908 in Grand Valley, Colorado, received his early education in Sebastopol, Calif. and his PhD at the University of Calif. at Berkeley. He was a college chemistry professor and later worked on the Manhattan Project which developed the atomic bomb. He was also appointed as a member of the Atomic Energy Commission and received many awards and honors for his accomplishments. His last position was on the faculty at UCLA before retiring, he passed away in 1980.
Radiocarbon dating is a common practice today in archeology, geology and paleontology. It does not work with inorganic substances such as rocks or wood which has become petrified. These substances are dated with other radioactive substances which take much longer to decay radioactively and are based on more unprovable assumptions.