The Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) has led a new international study published in the journal Quaternary Geochronology, about the direct dating of a fossil tooth of Homo antecessor from the unit TD6 of the archaeological site of Gran Dolina in the Sierra de Atapuerca (Burgos, Spain). In the work, a time range of between 772,000 and 949,000 years was found for this species of the Lower Pleistocene, so confirming earlier indirect datings.

In order to carry out this dating, a leading-edge methodology was employed, combining high-resolution Uranium-Thorium analysis using laser ablation coupled to a mass spectrometer and measurements of a fragment of enamel by Electron Spin Resonance (ESR).

"We used the same special protocol that had previously worked successfully with the fossil remains of Homo naledi and the oldest Homo sapiens found outside Africa" says Mathieu Duval, member of the Geochronology and Geology Program of the CENIEH and now at the Australian Research Center for Human Evolution at Griffith University (Australia)

"By combining direct dating of the piece with a new, more precise paleomagnetic study of the deposits of the stratigraphic unit TD6, it was possible to obtain a dating which is consistent with the previous indirect estimates based on the sediment or fauna associated to the hominin remains," the researcher adds.

Collective work

To obtain this dating and overcome the different challenges which arose over the study duration of almost three years, collaboration was needed from specialists in different scientific disciplines such as geochronologists, geologists, archaeologists and paleoanthropologists, among whom are included several researchers from the CENIEH such as Josep María Parés and José María Bermúdez de Castro, coordinators of the program, as well as Laura Martín-Francés and Isidoro Campaña.

Researchers attached to institutions based in Australia (Griffith University), Spain (IPHES, Complutense University of Madrid), France (University of Bordeaux) and China (University of Nanjíng), also collaborated.

Gran Dolina: a dating undergoing constant evolution

With the constant improvement over time of the analytical techniques and dating methods, it has been possible to progressively refine the chronology of the archaeological site of Gran Dolina since its initial study, published in 1995.

The present work joins other recent studies centering on the lower levels. In fact, relatively recently the chronology of the level TD4, where the oldest lithic industries of the site were identified, was successfully refined.

In TD1, it has likewise been possible to date a level at the base of the sedimentary fillings, where a change of magnetic polarity, identified as the Jaramillo event, was observed: this is very difficult to detect at archaeological sites in caves and it marks a very well-defined moment approximately one million years ago.

"Gran Dolina thus becomes one of the best-dated archaeological sites in the world, adding this new direct dating of a human fossil," says Bermúdez de Castro.

Read more at: https://phys.org/news/2018-05-dating...essor.html#jCp


The first direct ESR analysis of a hominin tooth from Atapuerca Gran Dolina TD-6 (Spain) supports the antiquity of Homo antecessor

Abstract



The present study reports the results of the first direct Electron Spin Resonance (ESR) dating study of Homo antecessor, the earliest known hominin species identified in Europe. The analysis of a tooth (ATD6-92) from TD6 unit of Atapuerca Gran Dolina (Spain) following a “semi non-destructive” procedure provides a final age estimate ranging from 624 to 949 ka, which covers all possible uranium uptake scenarios. Last, the additional magnetostratigraphic data collected within TD6 enables to further constrain the initial ESR chronology and to propose an age of between 772 and 949 ka for Homo antecessor, in agreement with previous dating works. Whereas our new results do not refine the existing chronology of stratigraphic unit TD6, they nevertheless support the antiquity of H. antecessor, which pre-dates the estimated divergence age of modern and archaic human lineages based on genetic evidence.


This work illustrates the challenges of dating human teeth by means of the ESR method, with the main pitfalls that are sometimes inherent to this specific application (e.g., systematic μCT-scanning of fossil hominin teeth; limited knowledge about the original sedimentary environment for teeth coming from old excavations; heterogeneous spatial distribution or the U-series elements in dental tissues). We identified several sources of uncertainty that may directly impact the accuracy of the age result. In particular, a slight contamination of dentine (<6%) in the enamel fragment measured by ESR was found to induce a significant age underestimation (33%) if not taken into consideration. It indeed caused not only a DE underestimation (by about 8%), but also produced a massive internal dose rate overestimation (by a factor of about 3.5). In contrast, other sources of uncertainty, such as the heterogeneity of the sedimentary environment, the variability of the water content over time, the previous μCT-scanning of the tooth or the potential preferential creation of unstable NOCORs in the ESR signal, showed here a limited impact on the final age result.

https://www.sciencedirect.com/scienc...383?via%3Dihub