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Measurements of 36CI in Polar Ice
- David Elmore, Nicholas J. Conard, Peter W. Kubik, Harry E. Gove, Martin Wahlen, Juerg Beer
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- Journal:
- Annals of Glaciology / Volume 10 / 1988
- Published online by Cambridge University Press:
- 20 January 2017, p. 202
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We are measuring 36Cl in the upper part of the 1966 Camp Century deep core, using the tandem-accelerator mass-spectrometry facility at the University of Rochester. There are two primary motivations for measuring 36Cl in ice. The first is to look for correlations between 36Cl concentrations and changes in solar activity. Previous studies of 10Be and 14C (Stuiver and Quay 1980, Raisbeck and others 1981, Beer and others 1983) have demonstrated that the production of these radio-isotopes increases during periods of low solar activity. When the sun is active, the magnetic field induced by the solar wind deflects galactic cosmic rays from the inner solar system and thereby lowers the production of radio-isotopes. Our study of 36Cl in ice dating back to A.D. 1550, from Camp Century, Greenland, shows that there was an increase in 36Cl production during the Maunder Minimum (1650–1715). However, climatic variations introduce fluctuations of a factor of 2 or more over short periods and the Maunder Minimum peak is only readily apparent when the data are smoothed mathematically.
The second motivation for measuring 36Cl in ice is to test the possibility that the ratio of 36Cl to 10Be will provide a means for dating ice over 50 000 years old (Nishiizumi and others 1983). The dependence on both solar activity and climatic fluctuations mentioned above precludes dating with a single radio-isotope. If, however, the production rates of 36Cl and 10Be are each proportional to the cosmic-ray flux and are transported identically to the ice sheet, these fluctuations would cancel and the ratio of 36Cl to 10Be would provide a radiometric means of dating very old ice. The half-lives for 36Cl (3.0 × 105 years) and 10Be (1.6 × 106 years), combine to give a “half-life” for the 36Cl/10Be ratio of 3.7 × 105 years.
Unfortunately, preliminary results from Camp Century, Greenland, show that it will almost certainly not be possible to use the 10Be/36Cl ratio for dating. 10Be and 36Cl have been measured in more than 20 samples; the 10Be/36Cl ratio varied, without any obvious pattern, from below 5 to over 15. Additional evidence comes from Antarctica. We found that the 10Be/36Cl ratio changed significantly within a short depth interval within a single block of ice and that the calculated age of ice based on 10Be/36Cl differed from the age of an embedded meteorite, ALHA82102 (personal communication from K. Nishiizumi).
A variation in the 10Be/36Cl ratio may be caused by climatic effects: for example, changes in air circulation between the stratosphere and the troposphere in the polar region, in combination with chemical processes that affect aerosol chlorine and beryllium differently. Also, the 10Be/36Cl ratio is smaller than expected, indicating that there may be additional sources of 36Cl. If there is a source of 36Cl that varies independently from the galactic cosmic-ray flux, this would result in variations in the isotope ratio. Discovery of the cause of the variations may result in a new tool for understanding paleoclimate.
An overview of the patterns of behavioural change in Africa and Eurasia during the Middle and Late Pleistocene
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- By Nicholas J. Conard, Institut für Ur- und Frühgeschichte und Archäologie des Mittelalters, Abteilung Ältere Urgeschichte und Quartärökologie, Eberhard-Karls-Universität Tübingen, Schloss Hohentübingen, 72070 Tübingen, Germany
- Edited by Francesco d'Errico, George Washington University, Washington DC, Lucinda Backwell, University of the Witwatersrand, Johannesburg
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- Book:
- From Tools to Symbols
- Published by:
- Wits University Press
- Published online:
- 04 June 2019
- Print publication:
- 01 June 2005, pp 294-332
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Summary
Abstract
This paper examines some large-scale patterns of behavioural change that are often viewed as indicators for the advent of cultural modernity and developed symbolic communication. Using examples from Africa and Eurasia, the paper reviews patterns of lithic and organic technology, subsistence and settlement as potential indicators of modern behaviour. These areas of research produce a mosaic picture of advanced technology and behavioural patterns that come and go during the late Middle and Late Pleistocene. Based on these data the emergence of modern behaviour, as seen in the archaeologically visible material record, appears to be gradual and heterogeneous in space and time. The evidence for the use of pigments is consistent with these data.
During the early part of the Late Pleistocene personal ornaments in the form of sea shells are documented in south-western Asia and southern Africa. By about 40 thousand years ago (Kya) a diverse array of personal ornaments is documented across the Old World in association with Neanderthals and anatomically modern humans in Europe. These include both modified natural objects and fully formed ornaments. The timing and distribution of the appearance of figurative art and other classes of artefacts including musical instruments point to a more punctuated development of fully modern behaviour during the middle of the Late Pleistocene at approximately 40 Kya. Due perhaps in part to the long and intense history of research much, but by no means all, of the relevant data come from Europe. Early figurative art from the Aurignacian of south-western Germany, northern Italy, Austria and southern France provides undisputed evidence for fully developed symbolic communication and behavioural modernity.
This paper also discusses some of the hypotheses for the development and spread of cultural modernity and rejects a strict monogenetic model in favour of a pattern of historically contingent, polygenetic development within a dynamic equilibrium between archaic and modern humans. The paper highlights the need for new refutable, regional and super-regional hypotheses for the advent and spread of behavioural modernity.
Résumé
Le présent article examine quelques-uns des aspects du changement comportemental généralement considéré comme indicateur de l'apparition d'une modernité culturelle et d'un système de communication symbolique élaboré. Sur la base d'exemples tirés d'Afrique et d'Eurasie nous passerons en revue la technologie lithique et en matière dure animale, les modes de subsistance et d'habitat comme vecteurs potentiels d'un comportement moderne.
Tools Underfoot: Human Trampling as an Agent of Lithic Artifact Edge Modification
- Sally McBrearty, Laura Bishop, Thomas Plummer, Robert Dewar, Nicholas Conard
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- Journal:
- American Antiquity / Volume 63 / Issue 1 / January 1998
- Published online by Cambridge University Press:
- 20 January 2017, pp. 108-129
- Print publication:
- January 1998
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A series of eight replication experiments tests the proposition that human trampling of stone flakes can produce edge damage that mimics deliberate retouch. Retouchlike edge damage, breakage, and other forms of macroscopic mechanical damage were observed on large numbers of pieces in all trampled sets. Experiments measured the relative contributions of three variables-raw material, artifact density, and substrate-in generating damage. Results indicate that while all three factors contribute to some degree, substrate plays the most decisive role, and that artifacts are more likely to exhibit damage if trampled on an impenetrable substrate. It was further found that trampling transforms flakes into pseudo-tools that can be classified as formal tools using a standard typology. Many of these are notched and denticulate pieces, indicating that special caution is needed in behavioral interpretations based on these tool types, and that the European Paleolithic Denticulate Mousterian industry requires critical reassessment.