How carbon dating is done

Not all materials can be radiocarbon dated. Most, if not all, organic compounds can be dated. Samples that have been radiocarbon dated since the inception of the method include charcoal , wood , twigs, seeds , bones , shells , leather, peat , lake mud, soil , hair, pottery , pollen , wall paintings, corals, blood residues, fabrics , paper or parchment, resins, and water , among others. Physical and chemical pretreatments are done on these materials to remove possible contaminants before they are analyzed for their radiocarbon content.

The radiocarbon age of a certain sample of unknown age can be determined by measuring its carbon 14 content and comparing the result to the carbon 14 activity in modern and background samples. The principal modern standard used by radiocarbon dating labs was the Oxalic Acid I obtained from the National Institute of Standards and Technology in Maryland. This oxalic acid came from sugar beets in When the stocks of Oxalic Acid I were almost fully consumed, another standard was made from a crop of French beet molasses.

Over the years, other secondary radiocarbon standards have been made. Radiocarbon activity of materials in the background is also determined to remove its contribution from results obtained during a sample analysis. Background samples analyzed are usually geological in origin of infinite age such as coal, lignite, and limestone. A radiocarbon measurement is termed a conventional radiocarbon age CRA. The CRA conventions include a usage of the Libby half-life, b usage of Oxalic Acid I or II or any appropriate secondary standard as the modern radiocarbon standard, c correction for sample isotopic fractionation to a normalized or base value of These values have been derived through statistical means.

American physical chemist Willard Libby led a team of scientists in the post World War II era to develop a method that measures radiocarbon activity. He is credited to be the first scientist to suggest that the unstable carbon isotope called radiocarbon or carbon 14 might exist in living matter. Libby and his team of scientists were able to publish a paper summarizing the first detection of radiocarbon in an organic sample.

Dating advances

It was also Mr. Now living plants 'breathe' CO 2 indiscriminately they don't care about isotopes one way or the other , and so while they are living they have the same ratio of carbon 14 in them as the atmosphere. Animals, including humans, consume plants a lot and animals that consume plants , and thus they also tend to have the same ratio of carbon 14 to carbon 12 atoms. This equilibrium persists in living organisms as long as they continue living, but when they die, they no longer 'breathe' or eat new 14 carbon isotopes Now it's fairly simple to determine how many total carbon atoms should be in a sample given its weight and chemical makeup.

And given the fact that the ratio of carbon 14 to carbon 12 in living organisms is approximately 1: In actually measuring these quantities, we take advantage of the fact that the rate of decay how many radioactive emissions occur per unit time is dependent on how many atoms there are in a sample this criteria leads to an exponential decay rate.

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We have devices to measure the radioactivity of a sample, and the ratio described above translates into a rate of Voila, now you can tell how old a sample of organic matter is. Carbon 14 dating is not great for dating things like a year old because if much less than 1 half-life has passed, barely any of the carbon 14 has decayed, and it is difficult to measure the difference in rates and know with certainty the time involved.

Radiocarbon dating is simply a measure of the level of 14 C isotope within the organic remains 8. This is not as clear-cut as it seems as the amount of 14 C isotopes in the atmosphere can vary.

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How is carbon dating done?

This is why calibration against objects whose age is known is required AMS works slightly differently; it converts the atoms of the sample into fast-moving ions so that they become charged atoms. By applying magnetic and electrical fields, the mass of these ions is measured and the accelerator is used to remove ions that might contaminate the dating. The sample passes through several accelerators in order to remove as many atoms as possible until the 14 C and some 12 C and 13 C pass into the detector.

These latter atoms are used as part of the calibration process to measure the relative number of isotopes 9. When the half-life was corrected in , the year was taken as a base date from which to calculate all resulting dates. It is presumed that the proportion of atmospheric 14 C is the same today as it was in 10 , 11 and that the half-life remains the same. If a radioactivity level comes back as half of what would have been expected if the organism had died in , then it is presumed to be 5, years before This does not mean that we have a precise year of BC, it means we then need to calibrate through other methods that will show us how atmospheric concentrations of the 14 C isotope has changed - most typically through the dendrochronology records tree ring data Very old trees such as North American Bristlecone Pine are ideal for constructing long and accurate records of the state of the atmosphere.

This allows researchers to account for variation by comparing the known records of 14 C levels in the tree record, looking for a tree record that has the same proportion of radiocarbon.

How Does Radiocarbon-14 Dating Work?

The overlapping nature of the tree records means this is the most accurate record we have. Archaeology was one of the first, and remains the major, disciplines to use radiocarbon dating and this is why many enter into the lab through combining chemistry and archaeological studies. It has a greater impact on our understanding of the human past than in any other field. Radiocarbon dating is profoundly useful in archaeology, especially since the dawn of the even more accurate AMS method when more accurate dates could be obtained for smaller sample sizes. One good example is a critical piece of research into the diet of the fragile Viking colonies of Greenland 13 for example; the study examined not just the 14 C dates of the people in the graves, but was also in examining their diet through examining the carbon isotopes themselves.

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The study concluded dates that were already suspected but not confirmed: There has been much debate about the age of The Shroud of Turin. It has become an important relic for many Catholics.


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The debate raged on for the decades after its discovery. Experts pointed to its medieval design, depiction of Christ and several other key factors marking it as in the region of years old.


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