It is a method to determine the age of plants and fossils. Carbon has three naturally occurring isotopes, C12, C13 and C14. Of the three, C14 is radioactive in nature and has a half-life (decays to half the strength) of 5,730 years. Scientists measure the strength of C14 in the plant or fossil, and compare it with the expected strength of C14 in the atmosphere, to compute the age. Also known as radio carbon dating, this technique was developed by Willard Libby in 1949. He was awarded the Nobel Prize in Chemistry in 1960.