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116: A new way to date bones
There is now a new way of dating skeletons. We will at some point in the near future have to send some samples off for analysis for carbon dating and DNA analysis. Now it appears there is a more accurate way but before we cover that, let's look briefly at how it is done now.
The various dating techniques available to archaeologists
Today's archaeologist has a wide variety of natural, electro-magnetic, chemical, and radio-metric dating methodologies available to her that can be used to accurately date objects that are just a few hundred years old as well as objects that are a few million years old with high accuracy in the right circumstances.
Natural Dating Techniques
One of the oldest natural dating techniques is geochronology, which is based on the principle of superposition -- an object, or layer, on top must have been placed there at a later point in time. Once a geologist has determined the absolute age of a geological formation, the archaeologist can assign an indirect date to objects found in the formation.
Natural sequence dating is based on the principle that as human behavior changes, so does the material products it produces. This allows an archaeologist, who is able to identify the attributes of a class of artifacts that are the most sensitive to change, to construct a sequence of those artifacts that accurately reflects the passage of time.
Chemical Dating Techniques
Aspartic amino acid racemization which can be used to date bones, teeth, and shells that are between 1,000 years and 1,000,000 years old (if calibrations to local climates are available). It's based on the fact that the chemical structures of amino acids found in all living things changes over time at a known rate given a known set of environmental conditions.
Another chemical dating technique available to archaeologists for dating bone is the bone-nitrogen dating technique. Bones buried in soil lose organic components, and nitrogen in particular, and gain inorganic components, such as fluorine and uranium, in their place. Since bones buried at the same time in the same deposit will lose nitrogen and gain fluorine and uranium at the same rate, an archaeologist can used this as a relative dating technique to determine if bones found in the same matrix were indeed deposited together.
Radiometric Dating Techniques
Radiometric dating techniques are based on the fact that unstable radioactive elements have regular rates of decay, or half-lives, that can be used as virtual clocks. Carbon-14 dating, which is based on the decay of carbon 14, with a half-life of 5730 years, to nitrogen-14 through beta-decay, measures the age of an organic object using the ratio of carbon-14 to carbon-12 that remains in the object.
Although carbon-14 dating is fairly accurate, since the concentration of carbon-14 in the atmosphere to carbon-12 has varied over time (due to changes in the earth's magnetic field, alterations in solar activity, and the industrial activities of humans), dates may only be off by a few decades for more recent objects More precisely, without calibrations, radiocarbon age determinations for items older than 3500 years old become increasingly inaccurate as you go back in time. One advantage of the carbon-14 method, which was one of the first radiometric dating methods developed, is that only a handful of charcoal, burned bone, shell, hair, wood, or other organic substance is required for laboratory analysis.
Summary of the old way:
The first thing is to approximate the date of the deposition of the bones, which is usually the same at the time since death. Confirmation is rarely obtained by collateral evidence and estimates are usually made in thesthholds of 30,70 or even 100 years. Bones in wet environments are harder to date than those in dry conditions (as our tall ones are). If one studies the organic sconstoitiuanst of the bones using techniques developed as far back as 1947. Nitrogen in protein loss. The fluorine dating - the process starts with cleaning the bone sample (in Dichloroindophenol as one method) and allowing to dry. N1 hydrochloric acid is used in tiny amounts to test effervescence. It was tested for the amount of nitrogen content, amino acid content and tested for benzidine reaction and ultra violet fluorescence. All these plus some others give an approximation of age based on a estimated scale.
Carbon dating is done much the same way as carbon deteriorates at a known rate in certain environments. Radiocarbon dating is a method for determining the age of an object by analysing the amount of radioactive carbon dioxide it contains. When an animal or plant dies, it stops exchanging carbon with its environment, and measuring the amount that remains provides a method of determining when it died.
The New Method - (From the European Society for Human Genetics)
Interest in the origins of human populations and their migration routes has increased greatly in recent years. A critical aspect of tracing migration events is dating them. However, the radiocarbon techniques*, that are commonly used to date and analyse DNA from ancient skeletons can be inaccurate and not always possible to apply. Inspired by the Geographic Population Structure model that can track mutations in DNA that are associated with geography, researchers have developed a new analytic method, the Time Population Structure (TPS), that uses mutations to predict time in order to date the ancient DNA.
TPS can calculate the mixtures of DNA deriving from different time periods to estimate its definitive age. "This introduces a completely new approach to dating. At this point, in its embryonic state, TPS has already shown that its results are very similar to those obtained with traditional radiocarbon dating. We found that the average difference between our age predictions on samples that existed up to 45,000 years ago, and those given by radiocarbon dating, was 800 years. This study adds a powerful instrument to the growing toolkit of paleo geneticists that can contribute to our understanding of ancient cultures, most of which are currently known from archaeology and ancient literature," says Dr Esposito.
Radiocarbon technology requires certain levels of radiocarbon on the skeleton, and this is not always available. In addition, it is a delicate procedure that can yield very different dates if done incorrectly. The new technique provides results similar to those obtained by radiocarbon dating, but using a completely new DNA-based approach that can complement radiocarbon dating or be used when radiocarbon dating is unreliable. "This permits us to open a powerful window on our past. The study of genetic data allows us to uncover long-lasting questions about migrations and population mixing in the past. In this context, dating ancient skeletons is of key importance for obtaining reliable and accurate results, " says Dr Esposito. " Through this work, together with other projects that we are working on in the lab, we will be able to achieve a better understanding of the historical developments that took place from the beginning of the Neolithic period, with the introduction of farming practices in Europe, and throughout the Bronze and Iron Ages. These periods include some of the most crucial events involving the population movements and replacements that shaped our world."
The technique is also expected to be valuable for genealogy. "When applying our ancient DNA dating technology to modern genomes, we have seen that some populations have more ancient genomes than others, and this can be helpful in establishing individual origins" says Dr Esposito.
Health research will benefit too. Since the study of genetic disorders is closely tied up with questions of ancestry and population stratification, being able to analyse the homogeneity of populations is of vital importance to epidemiologists. The researchers are currently compiling a larger dataset to increase the geographical/time coverage of their model and improve its accuracy. "Given the rapid increase in the number of ancient skeletons with published DNA, we believe that our technique will be useful to develop alternative hypotheses."
Chair of the ESHG conference, Professor Joris Veltman, Director of the Institute of Genetic Medicine at Newcastle University in Newcastle, United Kingdom, said: "This study shows how DNA derived from ancient skeletons can be used to more accurately determine the age of the skeleton than traditional radiocarbon tracing methods. This is another example of the power of modern genomics technologies to assist in helping us understand where we come from, how the journeys of our forefathers have helped shape our current genome and how this now impacts our current abilities and weaknesses, including risks of disease."
*Radiocarbon dating is a method for determining the age of an object by analysing the amount of radioactive carbon dioxide it contains. When an animal or plant dies, it stops exchanging carbon with its environment, and measuring the amount that remains provides a method of determining when it died.
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So when we are ready, we have a more accurate basis on which to present evidence to the world not only of age, but of origin. And all that in a more accurate way than what was possible up until now.
