Rainer Grün

Ages for the Middle Stone Age of southern Africa: implications for human behavior and dispersal.

The expansion of modern human populations in Africa 80,000 to 60,000 years ago and their initial exodus out of Africa have been tentatively linked to two phases of technological and behavioral innovation within the Middle Stone Age of southern Africa—the Still Bay and Howiesons Poort industries—that are associated with early evidence for symbols and personal ornaments. Establishing the correct sequence of events, however, has been hampered by inadequate chronologies. We report ages for nine sites from varied climatic and ecological zones across southern Africa that show that both industries were short-lived (5000 years or less), separated by about 7000 years, and coeval with genetic estimates of population expansion and exit times. Comparison with climatic records shows that these bursts of innovative behavior cannot be explained by environmental factors alone.

Electron spin resonance (ESR) dating

Abstract ESR dating has been systematically applied in earth sciences and archaeology since 1975 when Ikeya dated a stalactite from the Akiyoshi cave in Japan. In the meantime this new technique has been successfully applied to the dating of materials such as speleothems, spring deposited travertines, mollusc shells, corals, and tooth enamel. The present research focuses on the dating of quartz which allows the age assessment of heated ceramics, volcanic rocks, intrafault material, or windblown sediments. ESR dating is based on the measurement of the number of paramagnetic centers in a mineral. These centers are generated by alpha-, beta-, and gamma-radiation of the matural radioelements such as U, Th, and K, and have accumulated over time. Two parameters have to be determined: the accumulated dose (AD) and the dose rate (D) to which the sample was exposed. This review comprises three major parts: (a) introduction into ESR dating; (b) application of the method; and (c) appendices giving detailed description of dose rate calculation, physical basis of electron spin resonance, the ESR spectrometer and ESR lines. The major emphasis lies on the outline of the application of ESR dating. This includes the discussion of the ESR-signals of the various materials, sampling, sample preparation, and measurement techniques.

Earliest evidence of modern human life history in North African early Homo sapiens

Recent developmental studies demonstrate that early fossil hominins possessed shorter growth periods than living humans, implying disparate life histories. Analyses of incremental features in teeth provide an accurate means of assessing the age at death of developing dentitions, facilitating direct comparisons with fossil and modern humans. It is currently unknown when and where the prolonged modern human developmental condition originated. Here, an application of x-ray synchrotron microtomography reveals that an early Homo sapiens juvenile from Morocco dated at 160,000 years before present displays an equivalent degree of tooth development to modern European children at the same age. Crown formation times in the juveniles macrodont dentition are higher than modern human mean values, whereas root development is accelerated relative to modern humans but is less than living apes and some fossil hominins. The juvenile from Jebel Irhoud is currently the oldest-known member of Homo with a developmental pattern (degree of eruption, developmental stage, and crown formation time) that is more similar to modern H. sapiens than to earlier members of Homo. This study also underscores the continuing importance of North Africa for understanding the origins of human anatomical and behavioral modernity. Corresponding biological and cultural changes may have appeared relatively late in the course of human evolution.

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

Abstract 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) = Uo(t)p+1; Uo 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.

ESR dates for the hominid burial site of Qafzeh in Israel

Abstract Early modern hominids are found buried at the mouth of a cave at Qafzeh near Nazareth, Israel. They are associated with a Middle Paleolithic lithic industry. Previous dating of this site by TL analysis of burnt flint (Valladas et al., 1988) gave an age of 92 ± 5 kyr. We have now used the ESR method to date enamel of teeth of large mammals from the hominid-bearing layers. Assuming a constant rate of uptake of U through time by the teeth, we obtain an age of 115 ± 15 kyr. This is consistent with the TL results demonstrating early arrival of fully modern humans in Southwestern Asia.

ESR dating in quaternary geology

Abstract Electron spin resonance (ESR), a relatively new dating technique, was first suggested by Zeller et al. (1967) Zeller (1968) and Levy (1968). It has made substantial progress in frequent applications in the last few years. ESR-dating is based on the direct measurement of the amount of radiation-induced paramagnetic electrons trapped in crystal defects. These ‘free’ electrons were generated by alpha-, beta- and gamma-radiation of natural radioelements (e.g. U, Th, K) and have accumulated in the minerals over geologic time. The ESR-age is obtained by dividing the total amount of accumulated radiation dose (‘archaeological dose’, AD) by the dose per year (annual dose). This review comprises four major parts: The principles of the method, the determination of the archaeological dose (AD), the determination of the annual dose, and a compilation of datable materials. Several questions remain: the evaluation of the AD; the determination of the annual dose; and particularly with respect to the nature and stability of the electron traps used for dating.

New evidence for a 67,000-year-old human presence at Callao Cave, Luzon, Philippines

Documentation of early human migrations through Island Southeast Asia and Wallacea en route to Australia has always been problematic due to a lack of well-dated human skeletal remains. The best known modern humans are from Niah Cave in Borneo (40-42ka), and from Tabon Cave on the island of Palawan, southwest Philippines (47+/-11ka). The discovery of Homo floresiensis on the island of Flores in eastern Indonesia has also highlighted the possibilities of identifying new hominin species on islands in the region. Here, we report the discovery of a human third metatarsal from Callao Cave in northern Luzon. Direct dating of the specimen using U-series ablation has provided a minimum age estimate of 66.7+/-1ka, making it the oldest known human fossil in the Philippines. Its morphological features, as well as size and shape characteristics, indicate that the Callao metatarsal definitely belongs to the genus Homo. Morphometric analysis of the Callao metatarsal indicates that it has a gracile structure, close to that observed in other small-bodied Homo sapiens. Interestingly, the Callao metatarsal also falls within the morphological and size ranges of Homo habilis and H. floresiensis. Identifying whether the metatarsal represents the earliest record of H. sapiens so far recorded anywhere east of Wallaces Line requires further archaeological research, but its presence on the isolated island of Luzon over 65,000 years ago further demonstrates the abilities of humans to make open ocean crossings in the Late Pleistocene.

Speleothems, travertines, and paleoclimates

Abstract Age data for about 660 speleothems and about 140 spring-deposited travertines were collected, including many unpublished results. These data were plotted as histograms and also as error-weighted frequency curves on a 350,000-yr scale. These plots clearly show periods of increased speleothem/travertine growth as well as times of cessation. The periods of most frequent speleothem growth were between approximately 130,000 and 90,000 yr ago and since about 15,000 yr ago. Such periods before 150,000 yr ago, however, cannot be yet recognized because of a lack of sufficient data and the associated uncertainties of dates in this age range. A comparison with the oxygen-isotope record of deep-sea core V28–:238 shows a clear relationship, indicating that terrestrial calcite formation is controlled by paleoclimatic fluctuations. The evident climatic stimulation of Quaternary calcite formation is readily explained geochemically and is substantiated by the obvious difference in speleothem/travertine growth as a function of geographic position.

238U, 232Th profiling and U-series isotope analysis of fossil teeth by laser ablation-ICPMS

U and Th concentration profiles in fossil hominid and faunal teeth have been measured by laser ablation ICPMS. These profiles record diverse modes of U and Th uptake, particularly within enamel, that can be broadly related to the state of sample preservation. Observed U profiles are in general inconsistent with existing diffusion–adsorption models developed for U-uptake in bone and teeth. Where the models appear applicable, calculated diffusion rates are several orders of magnitude smaller than previous estimates. Laser ablation ICPMS offers a means of rapidly characterizing U and Th distributions in the enamel and dentine components of teeth as a precursor to ESR and U-series dating. In particular, it should allow the identification of teeth (and also bone) samples that have simple U-uptake histories and are amenable to precise dating by time-consuming and expensive Th–U and Pa–U TIMS techniques. We also demonstrated the use of laser ablation ICPMS to measure U-series isotopes in dentine and enamel samples with relatively high U concentrations (>20 ppm). These results, obtained using a quadrupole ICPMS, illustrate significant promise for in situ U-series isotope analysis, particularly when combined with the greater sensitivity and multi-collection capabilities of new sector ICPMS instrumentation. The latter may permit precise isotope ratio measurements on samples containing only a few ppm of U.

The Later Stone Age calvaria from Iwo Eleru, Nigeria: morphology and chronology

Background In recent years the Later Stone Age has been redated to a much deeper time depth than previously thought. At the same time, human remains from this time period are scarce in Africa, and even rarer in West Africa. The Iwo Eleru burial is one of the few human skeletal remains associated with Later Stone Age artifacts in that region with a proposed Pleistocene date. We undertook a morphometric reanalysis of this cranium in order to better assess its affinities. We also conducted Uranium-series dating to re-evaluate its chronology. Methodology/Principal Findings A 3-D geometric morphometric analysis of cranial landmarks and semilandmarks was conducted using a large comparative fossil and modern human sample. The measurements were collected in the form of three dimensional coordinates and processed using Generalized Procrustes Analysis. Principal components, canonical variates, Mahalanobis D2 and Procrustes distance analyses were performed. The results were further visualized by comparing specimen and mean configurations. Results point to a morphological similarity with late archaic African specimens dating to the Late Pleistocene. A long bone cortical fragment was made available for U-series analysis in order to re-date the specimen. The results (∼11.7–16.3 ka) support a terminal Pleistocene chronology for the Iwo Eleru burial as was also suggested by the original radiocarbon dating results and by stratigraphic evidence. Conclusions/Significance Our findings are in accordance with suggestions of deep population substructure in Africa and a complex evolutionary process for the origin of modern humans. They further highlight the dearth of hominin finds from West Africa, and underscore our real lack of knowledge of human evolution in that region.