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  • 1
    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
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  • 2
    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
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  • 3
    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
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  • 4
  • 5
    Publication Date: 1997-10-14
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 6
    Publication Date: 2015-12-24
    Description: The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2014-11-04
    Description: Late Cenozoic climate history in Africa was punctuated by episodes of variability, characterized by the appearance and disappearance of large freshwater lakes within the East African Rift Valley. In the Baringo-Bogoria basin, a well-dated sequence of diatomites and fluviolacustrine sediments documents the precessionally forced cycling of an extensive lake system between 2.70 Ma and 2.55 Ma. One diatomite unit was studied, using the oxygen isotope composition of diatom silica combined with X-ray fluorescence spectrometry and taxonomic assemblage changes, to explore the nature of climate variability during this interval. Data reveal a rapid onset and gradual decline of deepwater lake conditions, which exhibit millennial-scale cyclicity of ~1400–1700 yr, similar to late Quaternary Dansgaard-Oeschger events. These cycles are thought to reflect enhanced precipitation coincident with increased monsoonal strength, suggesting the existence of a teleconnection between the high latitudes and East Africa during this period. Such climatic variability could have affected faunal and floral evolution at the time.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 8
    Publication Date: 2013-08-02
    Description: The Indian Peak–Caliente caldera complex and its surrounding ignimbrite field were a major focus of explosive silicic activity in the eastern sector of the subduction-related southern Great Basin ignimbrite province during the middle Cenozoic (36–18 Ma) ignimbrite flareup. Caldera-forming activity migrated southward through time in response to rollback of the subducting lithosphere. Nine partly exposed, separate to partly overlapping source calderas and an equal number of concealed sources compose the Indian Peak–Caliente caldera complex. Calderas have diameters to as much as 60 km and are filled with as much as 5000 m of intracaldera tuff and wall-collapse breccias. More than 50 ignimbrite cooling units, including 22 of regional (〉100 km 3 ) extent, are distinguished on the basis of stratigraphic position, chemical and modal composition, 40 Ar/ 39 Ar age, and paleomagnetic direction. The most voluminous ash flows spread as far as 150 km from the caldera complex across a high plateau of limited relief—the Great Basin altiplano, which was created by late Paleozoic through Mesozoic orogenic deformation and crustal thickening. The resulting ignimbrite field covers a present area of ~60,000 km 2 in east-central Nevada and southwestern Utah. Before post-volcanic extension, ignimbrites had an estimated aggregate volume of ~33,000 km 3 . At least seven of the largest cooling units were produced by super-eruptions of more than 1000 km 3 . The largest, at 5900 km 3 , originally covered an area of 32,000 km 2 to outflow depths of hundreds of meters. Outflow ignimbrite sequences comprise as many as several cooling units from different sources with an aggregate thickness locally reaching a kilometer; sequences are almost everywhere conformable and lack substantial intervening erosional debris and angular discordances, thus manifesting a lack of synvolcanic crustal extension. Fallout ash in the mid-continent is associated with two of the super-eruptions. Ignimbrites are mostly calc-alkalic and high-K, a reflection of the unusually thick crust in which the magmas were created. They have a typical arc chemical signature and define a spectrum of compositions that ranges from high-silica (78 wt%) rhyolite to andesite (61 wt% silica). Rhyolite magmas were erupted in relatively small volumes more or less throughout the history of activity, but in a much larger volume after 24 Ma in the southern part of the caldera complex, creating ~10,000 km 3 of ignimbrite. The field has some rhyolite ignimbrites, the largest of which are in the south and were emplaced after 24 Ma. But the most distinctive attributes of the Indian Peak–Caliente field are two distinct classes of ignimbrite: 1. Super-eruptive monotonous intermediates. More or less uniform and unzoned deposits of dacitic ignimbrite that are phenocryst rich (to as much as ~50%) with plagioclase 〉 biotite quartz hornblende 〉 Fe-Ti oxides ± sanidine, pyroxene, and titanite; apatite and zircon are ubiquitous accessory phases. These tuffs were deposited at 31.13, 30.06, and 29.20 Ma in volumes of 2000, 5900, and 4400 km 3 , respectively, from overlapping, multicyclic calderas. A unique, and possibly kindred, phenocryst-rich latite-andesite ignimbrite with an outflow volume of 1100 km 3 was erupted at 22.56 Ma from a concealed source caldera to the south. 2. Trachydacitic Isom-type tuffs. Also relatively uniform but phenocryst poor (〈20%) with plagioclase 〉〉 clinopyroxene orthopyroxene Fe-Ti oxides 〉〉 apatite. These alkali-calcic tuffs are enriched in TiO 2 , K 2 O, P 2 O 5 , Ba, Nb, and Zr and depleted in CaO, MgO, Ni, and Cr, and have an arc chemical signature. Magmas were erupted from a concealed source immediately after and just to the southeast of the multicyclic monotonous intermediates. Most of their aggregate outflow volume of 1800 km 3 was erupted from 27.90 to 27.25 Ma. Nothing like this couplet of distinct ignimbrites, in such volumes, have been documented in other middle Cenozoic volcanic fields in the southwestern U.S. where the ignimbrite flareup is manifest. Magmas were created in unusually thick crust (as thick as 70 km) where large-scale inputs of mantle-derived basaltic magma powered partial melting, assimilation, mixing, and differentiation processes. Dacite and some rhyolite ignimbrites were derived from relatively low-temperature (700–800 °C), water-rich magmas that were a couple of log units more oxidized than the quartz-fayalite-magnetite (QFM) oxygen buffer at depths of ~8–12 km. In contrast to these "main-trend" magmas, trachydacitic Isom-type magmas were derived from drier and hotter (~950 °C) magmas originating deeper in the crust (to as deep as 30 km) by fractionation processes in andesitic differentiates of the mantle magma. "Off-trend" rhyolitic magmas that are both younger and older than the Isom type but possessed some of their same chemical characteristics possibly reflect an ancestry involving Isom-type magmas as well as main-trend rhyolitic magmas. Andesitic lavas extruded during the flareup but mostly after 25 Ma constitute a roughly estimated 12% of the volume of silicic ignimbrite, in contrast to major volcanic fields to the east, e.g., the Southern Rocky Mountain field, where the volume of intermediate-composition lavas exceeds that of silicic ignimbrites.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
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  • 9
    Publication Date: 2018-04-06
    Description: Development of the African Middle Stone Age (MSA) before 300,000 years ago raises the question of how environmental change influenced the evolution of behaviors characteristic of early Homo sapiens . We used temporally well-constrained sedimentological and paleoenvironmental data to investigate environmental dynamics before and after the appearance of the early MSA in the Olorgesailie basin, Kenya. In contrast to the Acheulean archeological record in the same basin, MSA sites are associated with a markedly different faunal community, more pronounced erosion-deposition cycles, tectonic activity, and enhanced wet-dry variability. Aspects of Acheulean technology in this region imply that, as early as 615,000 years ago, greater stone material selectivity and wider resource procurement coincided with an increased pace of land-lake fluctuation, potentially anticipating the adaptability of MSA hominins.
    Keywords: Anthropology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2018-04-06
    Description: The origin of the Middle Stone Age (MSA) marks the transition from a highly persistent mode of stone toolmaking, the Acheulean, to a period of increasing technological innovation and cultural indicators associated with the evolution of Homo sapiens . We used argon-40/argon-39 and uranium-series dating to calibrate the chronology of Acheulean and early MSA artifact–rich sedimentary deposits in the Olorgesailie basin, southern Kenya rift. We determined the age of late Acheulean tool assemblages from 615,000 to 499,000 years ago, after which a large technological and faunal transition occurred, with a definitive MSA lacking Acheulean elements beginning most likely by ~320,000 years ago, but at least by 305,000 years ago. These results establish the oldest repository of MSA artifacts in eastern Africa.
    Keywords: Anthropology, Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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