ESR Dating Of Tooth Enamel Research Articles

A very personal, 35 years long journey in ESR dating

This paper describes a personal journey in ESR dating and gives some insights of the progress made over 35 years in ESR dating of tooth enamel. When I started, samples were irradiated with four additive dose steps of 5, 10, 15 and 20 krad and the linear extrapolation yielded the dose value. An assumed dose rate of 100 mrad/a yielded the age of the sample. Since then I learned that one actually has to measure the dose rate. I also learned that the dose response can be described by a single saturating function, or perhaps two, and that errors can be appropriately calculated. Rather than having a single anisotropic CO2− radical, tooth enamel consists of two anisotropic CO2− radicals and two isotropic CO2− radicals, one stable, one unstable. Also, the dose response shows spatial differences in the production of these different radicals in response to beta and gamma rays. Then there is the problem of uranium uptake over time. We solved this by combining ESR and U-series analyses. We can even measure appropriate beta attenuation factors including sequential laser ablation U-series analyses. Even better, all analyses can be carried out on small enamel fragments, which can be glued back into their original position with little to no visible damage. Still, when using the most sophisticated dose rate calculations, they're often close to 1000 μGy a−1.

ESR dating of Lower Pleistocene fossil teeth: Limits of the single saturating exponential (SSE) function for the equivalent dose determination

In ESR dating of tooth enamel, a single saturating exponential (SSE) function is generally used to fit the dose response data points. This study shows several analytical and physical limits of this function when applied on Lower Pleistocene samples with expected ages in excess of one million years. We have checked other mathematical functions to obtain a closer fit to the analytical data. Indeed, the choice of the fitting function becomes crucial as this has a strong influence on the D E value. Among the functions used, the combination of a double saturating exponential (DSE) function provided the best approximation to the experimental points. The use of just one SSE function seems to lead to D E systematic overestimations if the D E values are >300 Gy.

Two types of CO2− radicals threaten the fundamentals of ESR dating of tooth enamel

In ESR dating of tooth enamel, dose values are usually obtained from powdered samples. It has been shown that the qualitative response of enamel powder to environmental and laboratory dosing is closely similar, thus apparently validating ESR protocols for dose estimation. When working on human fossils, their cultural and scientific value prevents the powdering of any samples. Measurements are carried out on enamel fragments instead. In fragments, natural and laboratory irradiations cause significantly different ESR responses. These can be attributed to two distinct CO2− radicals, one with apparently axial symmetry (orientated) and one that has no preferential orientation (non-orientated). The spectra of the naturally irradiated samples investigated here show a mix of about 90% of the orientated and about 10% of the non-orientated CO2− radicals. In contrast, laboratory irradiation induces a mix of about 60% orientated and 40% non-orientated CO2− radicals. Heating experiments show that the non-orientated CO2− radicals are significantly less stable than the orientated. This fact on its own would have serious implications for dose estimations, implying massive underestimations. It turns out, however, that with the heating induced decline of the non-orientated CO2− radicals, a larger number of orientated CO2− radicals is created. It is presently unclear whether these two processes are directly connected. In spite of very large internal reorganisations during these processes, powder spectra are only little affected by heating, because the powder spectra of both CO2− radicals are closely similar.The maximum differences that are observed on powder spectra in post-irradiation heating experiments, are in the range of 3%, dose values may be affected by a similar amount. However, when using preheating steps, which would occur when applying post-irradiation heating protocols to single aliquots, the thermal behaviour of the irradiated samples is quite different. While the annihilation of the non-orientated CO2− radicals has about the same decay rate in preheated and non-preheated samples, the increase of the orientated CO2− radicals is less pronounced in the preheated samples. As a result, overall intensity changes become critically dependent on the preheating times. The observed increase in signal intensity is in contrast to long-term fading experiments that showed that the ESR intensity of irradiated samples actually decreased over 6–12 years after laboratory irradiation. In view of this complexity and the small amount of quantitative information available, it is presently not possible to recommend any pre- or post-irradiation protocols.The good news for ESR dating is that any systematic errors introduced by a different mix of orientated and non-orientated CO2− radicals in the natural and irradiation spectra seem relatively small (<5%). At present, the most reliable way for the dose estimation of fragments seems to measure the samples rotating around the three principal axes and to merge the spectra to produce a powder-equivalent spectrum and use this for the construction of the dose response curve.

The problems in ESR dating of tooth enamel of Early Pleistocene and the age of Longgupo hominid, Wushan, China

Quite often ESR dating of tooth enamel provides underestimated ages. The factors, which may account for the age suppression are studied. For dating of the samples of Early Pleistocene, thermal fading of the g=2.0018 signal during the burial time may also lead toage underestimation. Isothermal annealing of the g=2.0018 line was studied in this work and a mixed first- and second-order kinetics was observed. Its implication to the practical dating purpose is discussed. It is suggested that if no uranium leakage is detected, ESR EU ages of Early Pleistocene enamel samples should be considered only as the lower limits of the true ages. Combined ESR and magnetic dating of the Longgupo profile, Wushan, China, assigns the Olduvai subchron to the fossil hominid-bearing layers of 7–8 of this profile.

The possibility of esr dating of tooth enamel of theEarly Pleistocene

The possibility of esr dating of tooth enamel of theEarly Pleistocene

ESR Dating of Tooth Enamel: Comparison with AMS 14C at El Castillo Cave, Spain

At El Castillo, in Cantabrian Spain, uncalibrated AMS 14C dating has shown the transition from Mousterian to Aurignacian to occur at 39·3±1·6 ka BP. We found ESR tooth enamel ages from the basal Aurignacian level at El Castillo to be 36·2±4·1 ka (early and linear uptake). The enamel and dentine had very low U contents, but ESR ages are strongly dependent upon knowledge of the moisture content history of the sediments. Although the Aurignacian ESR age is 8% younger than the weighted average uncalibrated AMS 14C age of 39·6±1·3 ka obtained from charcoal samples, we have shown that the methods agree within experimental uncertainty. However, since no precise 14C calibration yet exists for this period of time, we are unable to specify which of the ages is more accurate, nor are we able ascribe the apparent age discrepancy to a particular deficiency in the ESR method.

ESR dating of tooth enamel from Karain excavation (Antalya, Turkey)

Samples of fossil tooth enamesl taken from different depths of Karain Cave (Antalya, Turkey) were studied by the ESR method. The accumulated doses ( D ES of the samples were determined using the paramagnetic center at g = 2.0020 ± 0.0003 by means of three different microwave power conditions. It is found that the dating signal at g = 2.0020 ( ΔHpp ≈ 0.34 mT) is disturbed significantly by the isotropic signal at g = 2.0007 ± 0.0003 at high microwave power. The lifetime of this signal is significantly smaller than the lifetime of the dating signal. However, the statistical uncertainty caused by different microwave powers is still within the total uncertainty in the age determination of the tooth enamels under investigation. The ESR ages of the samples were calculated using early uranium (EU) and linear uranium (LU) uptake models. The ages due to EU and LU models are in agreement within an error of 10% due to the low uranium content of the samples.

ESR dating of tooth enamel: comparison with U-series, FT and TL dating at the Peking Man site

Deer tooth samples from Zhoukoudian, the Peking Man Cave, were studied. Non-linear fitting is used to determine AD, from which ESR ages were calculated by both the disequilibria model (DU) and linear uptake model (LU). Comparison of ESR ages with those from U-series, FT and TL methods show that the enamel of deer teeth is a suitable material for ESR dating.

Attempt at ESR dating of tooth enamel of French middle Pleistocene sites

Tooth enamel samples from four important French middle Pleistocene sites are analyzed by the ESR method. ESR ages were calculated using uranium uptake mathematical models and compared with U-series results.

ESR dating of tooth enamel: A comparison with KAr dating

The reliability of the ESR dating of tooth enamel was tested for a famous Italian Palaeolithic site, Isernia la Pineta, already dated by the KAr method. ESR ages, calculated with early uranium uptake model (EU), linear uranium uptake model (LU) and US-ESR model, are between 80 and 251 ka. The US model with the hypothesis of inverse correlation between ESR signal heights and uranium concentration resulted in an age of about 450 ka for one sample. These ages are compared with a KAr age of 736 ka.

ESR dating of tooth enamel: Coupled correction for U-uptake and U-series disequilibrium

ESR dates on tooth enamel require a knowledge of the history of uptake of uranium ( U ) by both the dentin and enamel. We present a method of determining the uptake history by simultaneously fitting a model uptake function to the U-series and accumulated dose data. The function is of the form U ( t ) = U o ( t ) p +1 ; U o is the observed U-238 content of the tooth; p is a parameter to be determined in the fitting procedure; T is the age of the sample, and U ( t ) is the U content at any time t .