Earth Sciences Research Journal Quaternary dating by electron spin resonance (ESR) applied to human tooth enamel used for estimating the free radical level and paramagnetic centres produced in some materials by ionising radiation. The ESR spectrometer at ANU is one of the most versatile spectrometers. Research School of Earth Sciences It has been shown repeatedly that it is difficult to date human fossils via associated material because in many instances, the human and allow the calculation of differential erosion rates in the Quaternary.
View transcript 0: And an age is actually the result of a long and complex analytical procedure. So we are going to show you here how we date a sample with the ESR method. The goal of this procedure is to try to estimate the radiation dose absorbed by the enamel layer during the geological time. So since the death of the organism.
UV-lamp, B: UV-Lampe, B. This important principle forms the basis of ESR dating of sediments. It is one of the most promising sub-disciplines in ESR dating.
The specific age range of ESR dating of quartz, possibly up to several Ma, makes sediment dating a potentially very valuable tool, with applications in geology, geography, prehistory and palaeoanthropology. The specific issue in ESR dating of sediments is the extent to which the geological clock is reset to zero, or to a value, which can be determined in the laboratory.
Resetting of the geological clock proceeds through sunlight bleaching of ESR centres during transport, prior to burial. Experimental bleaching curves are shown in Fig. The Al-centre contains an unbleachable residual, whereas Ti-centres can be fully or to a negligible level reset. Note that bleaching times are on the order of days to weeks. The most straightforward application of ESR dating of sedimentary quartz is that of aeolian sediments, because of the sunlight bleaching potential.
Since the Al-centre contains an important unbleachable residual with respect to natural sunlight radiation, it is important to mention that the ESR ages reported in these studies are corrected for this residual. The principle of this method is shown in Fig. Although the results show a strong underestimate relative to the independent age control of the loess, the method seems very promising if the residual dose can be determined very accurately. The problem of residual doses is less pertinent with Ti-related ESR centres because bleaching studies indicate that the ESR signal can be reset completely or at least to a negligible level with respect to deposits older than Late Pleistocene.
Correction for the unbleachable residual in ESR dating of quartz sediments using the Al-centre. The residual intensity is measured after prolonged bleaching and this level is used to infer the true palaeodose. Large differences are often encountered for individual Ti-related sub-centres in the regenerative dose method, but it is not clear yet whether this is due to sensitivity changes or not.
The first results Fig. ESR equivalent dose plot for Ti-centres from individual grains taken from a modern desert surface deposit, Eastern Desert, Egypt. Except for one grain no. Mit Ausnahme einer Messung Korn Nr. Despite proven difficulties with bleaching residuals related to the Al-centre in quartz, this specific ESR centre has been used in many studies to date sedimentary sequences spanning the whole Quaternary period, and even up to the Miocene.
A famous example of ESR dating of a fluvial terrace staircase is that from the Somme Basin, France, where consistent ESR results could be obtained relative to biostratigraphi- Electron spin resonance ESR dating of Quaternary materials cal, archaeological and palaeomagnetic data Fig. The same methodology, i. In this study, a consistent ESR dating pattern for deposits from the Tiglian up to the Tortonian around Ma was obtained. The quality of the ESR ages from these studies is guaranteed to some extent by bleaching experiments on recent fluvial deposits.
ESR dating of the River Somme terrace staircase. Only ESR ages on quartz are given. Other age control is available for the terrace sequence. This is confirmed by the ESR dates see arrow. Es sind nur Alter von Datierungen an Quarz dargestellt. Another point that should be kept in mind when evaluating such ESR dating results, is the targeted age range. Whereas, due to the slow bleaching behaviour, the Al-centre is probably inappropriate for detailed chronologies in the Late and late Middle Pleistocene, it may be a valuable tool for rough age determinations of extended Early Pleistocene and Pliocene sedimentary sequences, especially if other age-markers or suitable materials for dating are absent.
However, some fundamental issues in ESR dating using the Al-centre remain ambiguous. Up to the present, it is unclear how the irradiation spectrum of the solar lamp influences the magnitude of this residual. Lately, more attention has been paid to the use of Ti-centres for ESR dating of fluvial deposits from terrace staircases as well.
However, from detailed studies it has become clear that individual ages at the single-grain scale may vary considerably if Ti-centres are used BEERTEN et al. Together with sunlight bleaching, such grinding mechanisms could be an effective zeroing mechanism in ESR dating of glacially derived sediments.
As such, the Ge-related impurity centre in quartz appears to generate promising results, e. For instance, although growing with small artificial irradiation doses, it appears very difficult to find a natural Ge signal in quartz, as has been pointed out already by RINK The implication of this observation could be that the Ge centre is not stable at average burial temperatures. Generally, the additive dose method is used to determine the equivalent dose in quartz.
However, sometimes this approach may lead to large uncertainties for samples with a relatively large equivalent dose. In such cases, it would be advantageous to use the regenerative dose method. For ESR centres in quartz, artificial heating may be the most efficient and comfortable way of annealing the signal prior to regenerative dosing.
A major concern here is the possible presence of sensitivity changes i. Less comfortable in experimental terms, but much more related to the zeroing mechanism in sedimentary environments, is optical bleaching of ESR centres prior to administering the regenerative dose.
First results of this approach were recently published for Al-centres in loess YIN et al. Unfortunately, the ESR dose response is often found to be problematic in various quartz samples. Sometimes, strong inflexion points are found in the dose response of the Ti-centre and the Al-centre.
The most common applications in this framework include speleothems, foraminifera, and tooth enamel. Many ESR papers have published combined ESR and U-series dating results of speleothems stalagmites, stalactites , which generally show good agreement. A detailed review is given by RINK U-series dating methods. The authors see the possibility to date planctonic foraminifera up to approx. All in all, more studies on wellstratified deep sea cores in combination with independent age controls are needed to show Electron spin resonance ESR dating of Quaternary materials the potential and the limits of ESR dating of foraminifera.
So since the death of the organism. A few keys here to understand what I'm going to mention later on, is that ESR stands for Electron Spin Resonance, which is a spectroscopic analytical technique that looks at paramagnetic properties of materials. First we try to cut a piece of the tooth, and then we extract the different dental tissues.
The tooth is made by several dental tissues-- the enamel, but also dentine, and sometimes, the cement. So we need to extract them. We measure the thickness of the layer before and after cleaning. Once this is done, we powder the enamel. So at the end of the sample preparation, we have each dental tissue separated in a different vial, and the enamel powder. So the enamel powder is divided in various aliquots, which are subsamples of the same weight.
The samples are carefully weighed in small tubes before irradiation. Each aliquot is going to be irradiated at increasing dose. The idea is to understand the behaviour of the sample with the radiation. So after the radiation, the aliquots are carefully weighed in quartz tubes for ESR measurements. Each tube is placed in a resonator. As you can see here, this is a small metal box that is located between the two magnets.
For each tube, we record an ESR signal. This is the radiation- induced ESR signal that is measured for one tube. The intensity of the signal is directly dependent on the dose that has been absorbed by the sample. However, there is also a more advanced procedure that has been specifically designed to minimise the damage caused to the teeth.
This is essential when we work on highly valuable samples like human fossil teeth. There is no visible damage. So the procedure here is slightly different, compared with the standard approach. Once we receive the tooth, we take a few pictures of it, and then extract a piece of enamel.
We then, again, must clean the enamel in order to remove any kind of contamination from the adjacent dental tissues. Once we have a piece of enamel, we measure its thickness. So we use a teflon holder in which we mount a piece of parafilm. And once the parafilm is cooler, it becomes harder and saves the shape of the fragment. The objective of this procedure is to make sure that the fragment will be systematically measured in the exact same position.
Then the sample is fixed at the bottom of a quartz tube and measured. The main difference here is that we have only one fragment, so one aliquot. Which means that we need to successively measure the fragment and then irradiate it. This is a single aliquot procedure. This is impossible with enamel fragment, so we use the single aliquot procedure, which consists of successively measuring with ESR and irradiating the same fragment.
They all form a part of the ESR dating method. Electron spin resonance ESR dating is a trapped charge dating method. The other trapped charge dating methods are thermoluminescence dating TL and optically stimulated luminescence OSL.
However, only ESR can be applied to bones and teeth and is therefore used for the direct dating of human fossils. Trapped charge refers to the behaviour of the electrons within the material being tested. Here comes the science… Crystalline materials have their atoms arranged in an ordered structure called a lattice.
The structure of these lattices determines many of the physical properties of the material. The lattice has imperfections, or defects, where the arrangement of the molecules is not perfect — atoms may be missing in places, for example, creating holes in the lattice. These defects often have an electric charge. When the mineral is formed, all the electrons are where they belong: However, with radioactive irradiation like the one we used for killing off cancer cells in the hospital , electrons can be removed from the atoms and go on a journey through the crystal lattice.
Some of the electrons get trapped at these defects. Here we can measure them with ESR. We need teeth For ESR dating, we need teeth. They preserve the ESR signal in the hard minerals of the enamel. When we dig out a tooth at an archaeological site, it has an ESR signal.