# Simple definition of carbon dating

The technique used is called carbon dating, and in this lesson we will learn what this is and how it is used. Carbon dating, or radiocarbon dating, is a method used to date materials that once exchanged carbon dioxide with the atmosphere. In the late 1940s, an American physical chemist named Willard Libby first developed a method to measure radioactivity of carbon-14, a radioactive isotope.Libby was awarded the Nobel Prize in chemistry for his work in 1960.By knowing how much carbon-14 is left in a sample, the age of the organism and when it died can be worked out.Radiocarbon dating has been used extensively since its discovery.For example, if you start off with 1000 radioactive nuclei with a half-life of 10 days, you would have 500 left after 10 days; you would have 250 left after 20 days (2 half-lives); and so on.The half-life is always the same regardless of how many nuclei you have left, and this very useful property lies at the heart of radiocarbon dating. The graph below shows the decay curve (you may recognize it as an exponential decay) and it shows the amount, or percent, of carbon-14 remaining.

For the record, a beta-particle is a specific type of nuclear decay. Image 1 shows carbon-14 production by high energy neutrons hitting nitrogen-14 atoms, while in Image 2, carbon-14 naturally decomposes through beta-particle production.Once an organism is dead, however, no new carbon is actively absorbed by its tissues, and its carbon 14 gradually decays.Libby thus reasoned that by measuring carbon 14 levels in the remains of an organism that died long ago, one could estimate the time of its death.This is why radiocarbon dating is only useful for dating objects up to around 50,000 years old (about 10 half-lives).Radioactive carbon-14 is continually formed in the atmosphere by the bombardment of cosmic ray neutrons on nitrogen-14 atoms.