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  • 1
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    The New CLOCIT Irradiation Facility for 40Ar/39Ar Geochronology: Characterisation, Comparison with CLICIT and Implications for High‐Precision Geochronology (2018)
    Wiley
    Details
    Publication Date: 2018
    Description: Key Points The new CLOCIT irradiation facility for 40Ar/39Ar geochronology provides 55% of the flux of CLICIT with similar production rate ratios for interfering reactions. Radial fluence gradients in CLOCIT vary between irradiations ranging 0.2–4.2% cm−1. The non‐planar component of the fluence field can be resolved in CLOCIT and CLICIT and is significant for high‐precision geochronology . The Cadmium‐Lined Outer‐Core Irradiation Tube (CLOCIT) is a new irradiation facility for 40Ar/39Ar geochronology at the Oregon State University TRIGA® reactor. We report fluence (i.e., time‐integrated flux) parameters from the first four CLOCIT irradiations and compare them with the existing Cadmium‐Lined Inner‐Core Irradiation Tube (CLICIT). CLOCIT provides an average neutron flux equivalent of 1.45–1.53 × 10−4 J h−1; about 55% of CLICIT. Radial fluence gradients were on the order of 0.2–4.2% cm−1. A planar fit of J‐values results in residuals in the range of uncertainty in the J‐value, but systematic deviations resolve a non‐planar component of the neutron flux field, which has also been observed in CLICIT. Axial neutron fluence gradients were 0.6–1% cm−1, compared with 0.7–1.6% cm−1 for the CLICIT. Production rate ratios of interfering reactions were (40Ar/39Ar)K = (4 ± 6) × 10−4 and (38Ar/39Ar)K = (1.208 ± 0.002) × 10−2, (36Ar/37Ar)Ca =  (2.649 ± 0.014) × 10−4, (38Ar/37Ar)Ca =  (3.33 ± 0.12) × 10−5 and (39Ar/37Ar)Ca =  (9.1 ± 0.28) × 10−4, similar to the CLICIT values.
    Print ISSN: 1639-4488
    Electronic ISSN: 1751-908X
    Topics: Geosciences
    Published by Wiley
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  • 2
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    Time scales of critical events around the Cretaceous-Paleogene boundary (2013)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2013-02-09
    Description: Mass extinctions manifest in Earth's geologic record were turning points in biotic evolution. We present (40)Ar/(39)Ar data that establish synchrony between the Cretaceous-Paleogene boundary and associated mass extinctions with the Chicxulub bolide impact to within 32,000 years. Perturbation of the atmospheric carbon cycle at the boundary likely lasted less than 5000 years, exhibiting a recovery time scale two to three orders of magnitude shorter than that of the major ocean basins. Low-diversity mammalian fauna in the western Williston Basin persisted for as little as 20,000 years after the impact. The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Renne, Paul R -- Deino, Alan L -- Hilgen, Frederik J -- Kuiper, Klaudia F -- Mark, Darren F -- Mitchell, William S 3rd -- Morgan, Leah E -- Mundil, Roland -- Smit, Jan -- New York, N.Y. -- Science. 2013 Feb 8;339(6120):684-7. doi: 10.1126/science.1230492.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA. prenne@bgc.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23393261" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Argon ; Chronology as Topic ; *Ecosystem ; *Extinction, Biological ; Geologic Sediments ; Mammals ; Mexico ; *Minor Planets ; Radioisotopes ; Radiometric Dating
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Late Pliocene Homo and hominid land use from Western Olduvai Gorge, Tanzania (2003)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2003-02-22
    Description: Excavation in the previously little-explored western portion of Olduvai Gorge indicates that hominid land use of the eastern paleobasin extended at least episodically to the west. Finds included a dentally complete Homo maxilla (OH 65) with lower face, Oldowan stone artifacts, and butchery-marked bones dated to be between 1.84 and 1.79 million years old. The hominid shows strong affinities to the KNM ER 1470 cranium from Kenya (Homo rudolfensis), a morphotype previously unrecognized at Olduvai. ER 1470 and OH 65 can be accommodated in the H. habilis holotype, casting doubt on H. rudolfensis as a biologically valid taxon.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Blumenschine, Robert J -- Peters, Charles R -- Masao, Fidelis T -- Clarke, Ronald J -- Deino, Alan L -- Hay, Richard L -- Swisher, Carl C -- Stanistreet, Ian G -- Ashley, Gail M -- McHenry, Lindsay J -- Sikes, Nancy E -- Van Der Merwe, Nikolaas J -- Tactikos, Joanne C -- Cushing, Amy E -- Deocampo, Daniel M -- Njau, Jackson K -- Ebert, James I -- New York, N.Y. -- Science. 2003 Feb 21;299(5610):1217-21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Human Evolutionary Studies, Department of Anthropology, 131 George Street, Rutgers University, New Brunswick, NJ 08901-1414, USA. rjb@rci.rutgers.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12595689" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Dentition ; Environment ; Facial Bones/anatomy & histology ; *Fossils ; *Hominidae/anatomy & histology/classification ; Humans ; Life Style ; Mandible/anatomy & histology ; Maxilla/anatomy & histology ; Paleodontology ; Paleontology ; Seasons ; Skull/anatomy & histology ; Tanzania ; Terminology as Topic ; Tooth/anatomy & histology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Progressive aridification in East Africa over the last half million years and implications for human evolution [Earth, Atmospheric, and Planetary Sciences] (2018)
    National Academy of Sciences
    Details
    Publication Date: 2018-10-31
    Description: Evidence for Quaternary climate change in East Africa has been derived from outcrops on land and lake cores and from marine dust, leaf wax, and pollen records. These data have previously been used to evaluate the impact of climate change on hominin evolution, but correlations have proved to be difficult,...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 5
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    Paleoanthropology. Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-03-06
    Description: Sedimentary basins in eastern Africa preserve a record of continental rifting and contain important fossil assemblages for interpreting hominin evolution. However, the record of hominin evolution between 3 and 2.5 million years ago (Ma) is poorly documented in surface outcrops, particularly in Afar, Ethiopia. Here we present the discovery of a 2.84- to 2.58-million-year-old fossil and hominin-bearing sediments in the Ledi-Geraru research area of Afar, Ethiopia, that have produced the earliest record of the genus Homo. Vertebrate fossils record a faunal turnover indicative of more open and probably arid habitats than those reconstructed earlier in this region, which is in broad agreement with hypotheses addressing the role of environmental forcing in hominin evolution at this time. Geological analyses constrain depositional and structural models of Afar and date the LD 350-1 Homo mandible to 2.80 to 2.75 Ma.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉DiMaggio, Erin N -- Campisano, Christopher J -- Rowan, John -- Dupont-Nivet, Guillaume -- Deino, Alan L -- Bibi, Faysal -- Lewis, Margaret E -- Souron, Antoine -- Garello, Dominique -- Werdelin, Lars -- Reed, Kaye E -- Arrowsmith, J Ramon -- New York, N.Y. -- Science. 2015 Mar 20;347(6228):1355-9. doi: 10.1126/science.aaa1415. Epub 2015 Mar 4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA. dimaggio@psu.edu kreed@asu.edu. ; Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, USA. ; CNRS Geosciences Rennes, Campus de Beaulieu, 35042 Rennes, France. ; Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA. ; Museum fur Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany. ; Biology Program, Stockton University, 101 Vera King Farris Drive, Galloway, NJ 08205, USA. ; Human Evolution Research Center, University of California, Berkeley, 3101 Valley Life Sciences Building, Berkeley, CA, 94720-3160, USA. ; School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA. ; Swedish Museum of Natural History, Department of Palaeobiology, Box 50007, SE-10405 Stockholm, Sweden.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25739409" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; *Ecosystem ; Ethiopia ; Fossils ; *Geologic Sediments ; *Hominidae
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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