Archaeologists often turn to physical science for help in determining ages of sites and/or materials. Electron spin resonance (ESR) has proven. Electron spin resonance (ESR) dating was introduced into archaeology about 20 years ago. Although the method is still in a rapid phase of development, it has. electron spin resonance (ESR) dating of tooth enamel, which, together with the related background, it is impossible to determine the location of the oldest Homo Bones and teeth occur in most archaeological sites and are commonly coeval.
Fossil teeth are usually collected either on site or chosen from collections. Large mammal teeth, and especially from herbivores, are usually preferred, since they offer a thicker enamel layer. Then, in situ measurements of the natural radioactivity at the exact place where the sample was collected during excavations, or at least the closest possible, is carried out to evaluate the gamma dose rate.
Classically, various techniques may be employed: In the laboratory, the fossil tooth is prepared by separating mechanically each dental tissue.
The enamel layer is then cleaned, usually with a dentist drill, and gently powdered, in order to avoid significant angular dependence of the EPR signal within the resonator and to improve sample homogeneity.
Electron spin resonance dating - Wikipedia
This is why EPR must be considered as a destructive dating method. Each aliquot is then measured at room temperature by EPR spectrometry in order to study the behaviour of the EPR signal with the increasing dose values see Figure 1. Routine quantitative measurements are usually performed by X-band EPR spectrometry, since it offers a good compromise between sensitivity and measurement repeatability in comparison with higher frequency bands.
The experimental setup for quantitative EPR measurements is specifically designed to ensure the stability of the system, including air conditioning and chiller to control the temperature of the water circulating in the magnet.
Measurements are thus performed under controlled experimental conditions and following a standardised analytical protocol, in order to minimise any sources of uncertainty that could affect the repeatability of the measurements see further details in Duval et al.
EPR intensities are then extracted from each spectrum, usually by peak-to-peak measurements between T1 and B2 Figure 1 and plotted vs the irradiation doses in order to obtain a growth curve or dose response curve. A given function, usually a single saturating exponential or a double saturating exponential function, is fitted through the EPR experimental data points.
By definition, this function is supposed to describe the behaviour of the radiation-induced EPR signal of tooth enamel since the death of the animal i. If the gamma dose rate is assessed in situ, the beta dose rate from the sediment if it applies should preferably be assessed in the laboratory from the sediment sample that was collected around the tooth.
Various laboratory analytical techniques may be used to calculate the radioelement contents of the sediment, e. Other techniques, like beta counting for example, may directly provide a total beta or gamma dose rate value. To do so, mass spectrometry techniques are now usually employed [e. This is done via tables, and the value depends on the depth of the sample, as well as the density of the sedimentary matrix, latitude and altitude of the site.
EPR age calculation of fossil teeth is not so straightforward since it may involve up to 25 parameters. In addition to this, the dose rate in dental tissues is not constant over time but has to be modelled from the U-series data collected.
An EPR age may be obtained by iteratively solving the integral Equation 1since there is only one solution for which the total dose rate built up over time will match the DE value. Not every chronometric dating method can be used on a given Prehistoric site, since by definition it depends on the presence or absence of suitable materials for this purpose, which is closely related to the geological context and the presumed age of the site.
Figure 3 shows the time range applicability for some of the most used dating techniques in Quaternary studies.
EPR is one of the very few dating methods that may be applied to fossil remains. By definition, the dating of a tooth remains provides a direct dating of hominid or animal occupations, whereas other numerical methods can only date the sedimentary matrix that is enclosing the archaeo—palaeontological materials.
Consequently, this application may be also potentially used in any sedimentary context, while other methods like Argon—Argon or cosmogenic nuclides dating can only be used on volcanic minerals and quartz grains, respectively. In addition, the EPR technique is one of the very few possibilities to date fossil remains beyond the C and U-series dating time range.ESR -Electron Spin Resonance- - principle, working & application
C, U—Th, Ar—Ar; an overview may be found in Reference 12this is nevertheless one of the few methods that can be used for the Early Pleistocene period 2. This is a key period in European Prehistory, marked by the arrival of the first hominids in the continent and who very likely spread from Georgia, about 1.
EPR has definitely an important role to play for the improvement of the chronological framework of the oldest hominids settlements in Europe. This is very likely due to the long and complex analytical process that requires a large diversity of equipment e.
U-series analyses facilities, EPR spectrometer, gamma irradiation source, high resolution gamma spectrometer, portable gamma spectrometerwhich make it especially complicated to setup a complete and autonomous laboratory. However, recent developments in the field have demonstrated the potential of this method for Quaternary geochronology. Among them, the development of almost non-destructive direct dating of hominid fossil teeth is perhaps the most promising.
If EPR spectroscopy is not a destructive method per se, the standard procedure consists in working with enamel powder, mainly for practical reasons, to avoid the complexity induced by EPR signal anisotropy.
For a long time, this aspect has significantly limited the access to rare samples, like hominid teeth. Once the analyses are done, the fragment may be inserted back into the tooth in its original position.
Quaternary dating by electron spin resonance (ESR) applied to human tooth enamel
This new approach offers interesting perspectives for the EPR method by allowing direct dating of hominid remains that are beyond the 14 C time range. World Scientific, Singapore Isotopes 62, — Isotopes 68, — Mineralogical Society of America, pp.
D 14 1—2— Guilarte Moreno and R. Each sample's radiation sensitivity is individually calibrated for dose assessment by the additive dose method; each sample is incrementally irradiated with at least 14 additional doses up to Gy or more avoiding the sample becoming saturated. A linear regression analysis is applied to the ESR measurements at each dose increment and the original measurement laboratory-un-irradiated sample.
The original DA in the sample is obtained from the negative intercept of the regression line with the dose axis; is estimated as being the total radiation provided by all radioactive elements present in a sample and soil and also cosmic radiation Ikeya ; Jonas ; Walker ; Grun Materials and Methods The dentine was initially removed from teeth using a dental drill and water cooling.
The molar enamel powder was divided into nine aliquots. The spectrometer parameters used were: Soil samples were also collected from the Aguazuque site and sent for U, Th and K content analysis by gamma spectrometry. Radiometric analysis is widely used for determining natural radioisotopes in geological samples by means of spectroscopic methods and, especially, for quantifying the uranium, thorium and potassium present in samples.
A linear model was used for fitting ESR signal intensity to dose, as has been done by other authors Baffa et al.
Dating fossil teeth by electron paramagnetic resonance: how is that possible?
ROSY software Brennan et al. Soil water content was The software's default values were used for the remaining parameters. Finding the dose rate to convert DA into an age is a crucial step after DA has been found. ROSY software allows age to be calculated from an enamel sample by taking DA due to radioisotopes from adjacent layers into account. The software computes age based on three uranium absorption models linear, early uptake and a combination of both. Table 1 shows the soil analysis results.
The present work did not determine U, Th and K concentration in enamel and dentine as their percentages have been negligible for calculating age in previous work, especially in dates for the Holocene period Kinoshita et al. Typical soil density, enamel and dentine values were used for calculating age 2.
Using these values and the radioisotope concentrations listed in Table 1ROSY software was used for obtaining the alpha, beta and gamma radiation dose rate contribution for each radioisotope in sediment the results are listed in Table 2. These results were the same for any uranium absorption model. It should be noted that ROSY software calculates these ages using three uranium accumulation models: The way that uranium accumulates in a tooth is established by these models; accumulation increases at the same rate as time in the linear model and accumulation occurs in a short period of time in the early model, relative to a tooth's age and then remains constant after this short period of time.
The tooth's age was the same when calculated by these three methods; this result was consistent if taken into account that the accumulation of radioactive elements inside the tooth was negligible. Conclusions Age determined at many countries' archaeological sites is the result of radiocarbon 14C analysis of particular items found around the burials and not direct dating of individuals found there.
The results regarding either physical or geological phenomena may not be chronologically equal, hence the importance of having techniques like ESR which can directly and absolutely determine the age of individuals of interest. This result agreed with stratigraphic analysis at sites providing soil ages ranging from 2, to 3,y BP for 50 and 80 cm depths Correal, ESR dating accuracy was obtained relatively straightforwardly, using just a few grams of tooth enamel, thereby highlighting some of the advantages and characteristics of the ESR dating method.
The results so obtained have contributed towards joining links in the long chain of Colombian and American history where there is still much to do, due to the rich pre-Hispanic and colonial past. This paper thus represents a pioneering effort aimed at promoting the dating of our ancestors.
Rodriguez, for providing facilities and allowing the use of his samples, as well as AM Groot archaeologist for her support during this research. ESR dating of a toxodon tooth from a Brazilian karstic cave. Direct Dating of Human Fossils. Free Radicals in Biology and Medicine. Advances in ESR Applications. Use of electron paramagnetic resonance dosimetry with tooth enamel for retrospective dose assessment.