As isotopes break down, or decay they give off radiation. Materials that decompose in this way are said to have a 'half-life'. As the quantity of material present decreases, so does the actual rate at which the material decays. The process of dating artifacts by radioactive C-14 measurement depends strictly upon this condition. Using C-14 measurement and analysis it is possible to obtain a reasonably accurate estimate of the age of materials, given certain conditions.
Carbon-based materials such as wood, bone, and other organic materials, come from sources that were once living and in a dynamic relationship with their environment. Organic fibers that come from sourcessuch as trees, flax, cotton, and wool, grow through or depend on the process of photosynthesis. In photosynthesis, carbon dioxide is incorporated with water to produce the structural fiber cellulose and related compounds. Due to the influx of background radiation from terrestrial sources and 'cosmic rays', there is a fairly constant percentage of carbon dioxide in which the carbon atom is radioactive C-14 rather than non-radioactive C-12. While the plant is alive, this radioactive carbon dioxide is incorporated into the photosynthetic process at a constant corresponding rate, providing a baseline composition ratio of C-14 to C-12.
When the plant is killed, photosynthesis ceases and the relative amount of C-14 in the material begins to decrease from the baseline quantity. By relating the amount of C-14 remaining in the artifact material to the baseline amount of C-14 in living systems, a fairly accurate estimate can be had of the amount of time that has passed since the artifact was produced, according to the number of half-lives that have transpired. An invaluable tool for archeologists.
About the Author
Richard M J Renneboog, MS
Richard M. J. Renneboog is an independent private technical consultant and writer in both chemical and computer applications. Endeavors have included preparation of scripts for instructional and promotional video, corporate website design, curriculum development for training in advanced composites technology, and development.