Carbon (C-12) is a principal organic element which constantly moves in and out of the food chain. As long as an organism is part of the food chain, the amount of carbon in its cells is constant and at the same level as the C-12 atmospheric content. This principle also applies to C-14 – a radioactive isotope of carbon that has two extra neutrons. The C-14 isotope naturally occurs in minute amounts, slowly decays into nitrogen (N-14) and is harmless to living organisms. When an organism dies, the quantity of C-14 slowly drops over the course of thousands of years, as it transforms into N-14. The radiocarbon method used to date archaeological, geological, and hydrogeological samples (which can be up to 60,000 year old) is based on the fact that C-14 is present in organic materials.
Detonations of nuclear bombs into the atmosphere after World War II and up until 1960 have affected the content of radioactive trace materials in the air. They have created “the C-14 bomb pulse”, doubling the quantity of C-14 in the atmosphere. Since 1960, the atmospheric C-14 levels have slowly decreased back to the natural levels. The sudden change in atmospheric C-14 levels had an impact on the entire food chain and therefore, on organic materials. Even the lens crystallins of our eyes absorbed the increased carbon content through food we consumed.
Crystallins are transparent proteins which constitute the lens of the human eye. They are arranged in a particular way that allows light to pass through the lens so that we can see. From conception and up to 1-2 years of age, the crystallins build up in the lens. From then on, however, they remain essentially unchanged for the rest of our lives. In fact, crystallins reflect the content of C-14 present in the atmosphere at the time of their creation shortly after birth.
Physicists at the Department of Eye Pathology and the Department of Physics and Astronomy at Arhus University, Denmark, together with associate Professor Niels Lynnerup from the Department of Forensic Sciences at the University of Copenhagen, developed a forensic method that utilizes a large nuclear accelerator to determine the amount of C-14 in lens tissue. Using this method, as little as one milligram of C-14 can be detected, allowing scientists to calculate the specific person’s year of birth.
According to Professor Lynnerup, the technique may have several other applications: “We think that the carbon dating of proteins and other molecules in the human body can also be used to study when certain kinds of tissue are generated and regenerated. This could, for example, be applied to cancer tissue and cancer cells. Calculating the amount of C-14 in these tissues could perhaps tell us when the cancerous tissues formed, and this could further the understanding of cancer.” he explains.
TFOT previously covered several other carbon-based applications, which utilize carbon nanotubes. Such nanotubes are used for radiotherapy treatment of cancerous cells, while nanotubes which are faster and longer than ever before are being developed as electricity conductors for electrical uses.
The research article describing the eye-lens C-14 dating method is available in the online, open-access journal PLoS ONE.