What can radiocarbon dating be used on

Rachel Wood does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Republish our articles for free, online or in print, under Creative Commons licence. Radiocarbon dating has transformed our understanding of the past 50, years. Professor Willard Libby produced the first radiocarbon dates in and was later awarded the Nobel Prize for his efforts. Radiocarbon dating works by comparing the three different isotopes of carbon. Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons.

This means that although they are very similar chemically, they have different masses. The total mass of the isotope is indicated by the numerical superscript. While the lighter isotopes 12 C and 13 C are stable, the heaviest isotope 14 C radiocarbon is radioactive. This means its nucleus is so large that it is unstable.

Over time 14 C decays to nitrogen 14 N. Most 14 C is produced in the upper atmosphere where neutrons, which are produced by cosmic rays , react with 14 N atoms. This CO 2 is used in photosynthesis by plants, and from here is passed through the food chain see figure 1, below. Every plant and animal in this chain including us!

History of Radiocarbon-14 Dating

When living things die, tissue is no longer being replaced and the radioactive decay of 14 C becomes apparent. Around 55, years later, so much 14 C has decayed that what remains can no longer be measured. In 5, years half of the 14 C in a sample will decay see figure 1, below. Therefore, if we know the 14 C: Unfortunately, neither are straightforward to determine. The amount of 14 C in the atmosphere, and therefore in plants and animals, has not always been constant. For instance, the amount varies according to how many cosmic rays reach Earth.

Luckily, we can measure these fluctuations in samples that are dated by other methods. Tree rings can be counted and their radiocarbon content measured. A huge amount of work is currently underway to extend and improve the calibration curve. In we could only calibrate radiocarbon dates until 26, years.

Now the curve extends tentatively to 50, years. Radiocarbon dates are presented in two ways because of this complication. The uncalibrated date is given with the unit BP radiocarbon years before The calibrated date is also presented, either in BC or AD or with the unit calBP calibrated before present - before The second difficulty arises from the extremely low abundance of 14 C. Many labs now use an Accelerator Mass Spectrometer AMS , a machine that can detect and measure the presence of different isotopes, to count the individual 14 C atoms in a sample.

Australia has two machines dedicated to radiocarbon analysis, and they are out of reach for much of the developing world. In addition, samples need to be thoroughly cleaned to remove carbon contamination from glues and soil before dating.

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This is particularly important for very old samples. When an organism dies, it stops absorbing the radioactive isotope and immediately starts decaying 7. 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.

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. 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.

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. 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.

It wasn't until , and several subsequent tests since then, that this was confirmed 14 ; it is now the best-known example of the success of the AMS method as countless tests have been carried out and confirmed the dates.

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A significant portion of the Shroud would have been destroyed using the older method. The paper for the study is available online Each subsequent test has come back with dates of the mid 14 th century. Landscape Archaeology is a bridge between archaeology and environmental sciences though many consider it an environmental science in its own right. It is the study of how people in the past exploited and changed the environment around them. Typically, this will involve examining spores and pollen to examine when land was cleared of scrub and trees in the Neolithic Revolution to make way for crops.

It also makes use of phytoliths, entomological remains, GIS digital mapping , soil sampling, bone analyses, ground penetrating radar, and map studies and other documentary data. It has been fundamental, especially in Europe, to demonstrating how landscapes are relics and monuments in themselves and are worthy of study as such. Returning to the example of the Vikings in Greenland above, the extended study and dating of the faunal remains shows distinct changes that were made by the Vikings. The studies show the approximate date of arrival of European livestock and crops 13 and when these finally disappeared from the record