Carbon dating, or radiocarbon dating, is a method used to date materials that once exchanged carbon dioxide with the atmosphere. In other words, things that were living. In the late 1940s, American physical chemist Willard Libby first developed a method to measureradioactivity of carbon-14, a radioactiveisotope. Libby was awarded the Nobel Prize in chemistry for this work in 1960. Carbon dioxide in the atmosphere contains a constant amount of carbon-14, and as long as an organism is living, the amount of carbon-14 inside it is the same as the atmosphere. However, once the organism dies the amount of carbon-14 steadily decreases. By measuring the amount of carbon-14 left in the organism, it's possible to work out how old it is. This technique works well for materials up to around 50,000 years old.