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About 3000 years ago, a major vegetation change occurred in Central Africa, when rainforest trees were abruptly replaced by savannas. Up to this point, the consensus of the scientific community has been that the forest disturbance was caused by climate change. We show here that chemical weathering in Central Africa, reconstructed from geochemical analyses of a marine sediment core, intensified abruptly at the same period, departing substantially from the long-term weathering fluctuations related to the Late Quaternary climate. Evidence that this weathering event was also contemporaneous with the migration of Bantu-speaking farmers across Central Africa suggests that human land-use intensification at that time had already made a major impact on the rainforest.
Marine sediments suggest that climate was not the sole driver of the African rainforest crisis 3000 years ago.
The results from both weathering proxies can be explained by changing climate, except for the period between 3000 and 2000 years ago. During the African rainforest crisis of the first millennium B.C.E., both proxies show that weathering increased despite reduced precipitation and constant temperatures.
After a few insistent e-mails to the journal, Forget and Jansen were given the name of the submitted paper's corresponding author: Serge Valentin Pangou, director of the Study and Research Group on Biological Diversity (GERDIB) in Brazzaville, the Congo's capital. While GERDIB is not well known internationally, it is an important institution in the Congo that often carries out ecological and environmental studies for the government, researchers familiar with it say. And according to foreign scientists who have worked in the Congo, as its director, Pangou serves as a powerful gatekeeper who can grant research permits to them, as well as to Congolese graduate students and junior researchers.
New undergraduate students arriving to study physics at the University of Bristol from 1975 onwards have all taken the same test of their knowledge and understanding of physics and mathematics. Many of the questions test knowledge of material that has been in the A-level syllabus for maths or physics throughout this period. The ability of incoming students to answer these questions declined significantly in the 1990s with average scores falling from around 75 % up to 1990 to below 50 % after 2000 against a background of increasing A-level grades of the entrants to the programme. It is suggested that changes in teaching and examination methods have caused students to be less able to carry out multi-stage calculations and that the introduction of modular examinations may have encouraged a culture where students tend to forget material learnt in previous modules.
In an unusual attempt at scientific self-examination, psychology researchers are scrutinizing their field's reproducibility
Nosek first became interested in the problem of replication in psychology several years ago, after he started having persistent problems confirming others' results—something his lab routinely does before extending research to address new questions. Believing himself to be a careful methodologist, he wondered whether something was wrong with the studies he was attempting to reproduce.
Too many sloppy mistakes are creeping into scientific papers. Lab heads must look more rigorously at the data – and at themselves.
Seit eineinhalb Jahrzehnten forscht die Kommission für Archäologie Außereuropäischer Kulturen (KAAK) des DAI im Nordosten des Königreichs Marokko. Grund dafür war die ganz besondere geografische Situation an der Nahtstelle des afrikanischen zum europäischen Kontinent. Hier bot sich die Chance, nahezu in Sichtweite zwei ganz unterschiedliche Kulturkreise miteinander zu vergleichen.
An der Unterkante stieß man in 3 m Tiefe völlig unerwartet auf reiche Schichten des Mittelpaläolithikums. Sie wurden aufgrund mittels Beschleuniger-Massenspektrometrie erstellter Radiokarbondaten auf ein Alter von 50 000 bis 40 000 Jahren datiert. Zu diesem Zeitpunkt unterschieden wir dabei ein >Atérien< und, darunter, ein >Moustérien<, eine akkurat dem Lehrbuch entsprechende stratigrafische Situation. Im weiteren Verlauf der Grabungen, die wir inzwischen auf nahezu die Hälfte des 100 m2 messenden Abris ausgeweitet hatten, wurde der Schichtverlauf immer komplizierter und überraschender. Unter dem >Moustérien< folgte eine kompakte und geschlossene Calciumcarbonatschicht. Darunter befand sich erneut >Atérien<, unter dem schließlich wieder ein >Moustérien< lag. Diese eigenartige Interstratifikation, jüngst im Zentrum ergänzt um ein oberstes >Moustérien<, eliminiert logischerweise die verbreitete Vorstellung einer Abfolge Atérien – Moustérien und reduziert die beiden Komplexe auf ein übergeordnetes Mittelpaläolithikum. Daraufhin angefertigte umfangreiche TL-Datierungsserien an verbranntem Silex ergaben eine Abfolge von ca. 180000 bis 30000 Jahren. Somit liegt in Ifri n'Ammar das älteste gesicherte Mittelpaläolithikum Nordafrikas vor und zugleich mit ca. 135 000v.Chr. das älteste >Atérien<. Alle anderen bekannten Fundstellen im westlichen Maghreb setzen später ein.
The `radioactive dice' experiment is a commonly used classroom analogue to model the decay of radioactive nuclei. However, the value of the half-life obtained from this experiment differs significantly from that calculated for real nuclei decaying exponentially with the same decay constant. This article attempts to explain the discrepancy and suggests modifications to the experiment to minimize this effect.
A newly discovered partial hominin foot skeleton from eastern Africa indicates the presence of more than one hominin locomotor adaptation at the beginning of the Late Pliocene epoch. Here we show that new pedal elements, dated to about 3.4 million years ago, belong to a species that does not match the contemporaneous Australopithecus afarensis in its morphology and inferred locomotor adaptations, but instead are more similar to the earlier Ardipithecus ramidus in possessing an opposable great toe. This not only indicates the presence of more than one hominin species at the beginning of the Late Pliocene of eastern Africa, but also indicates the persistence of a species with Ar. ramidus-like locomotor adaptation into the Late Pliocene.
A fossil foot found in Ethiopia suggests that human ancestors that walked on two feet and also ably climbed trees existed until 3.4 million years ago, adding evidence for locomotor diversity during early human evolution.
Human hunting was responsible for the extinction of large mammal species in tropical Australia.
Although an African origin of the modern human species is generally accepted, the evolutionary processes involved in the speciation, geographical spread, and eventual extinction of archaic humans outside of Africa are much debated. An additional complexity has been the recent evidence of limited interbreeding between modern humans and the Neandertals and Denisovans. Modern human migrations and interactions began during the buildup to the Last Glacial Maximum, starting about 100,000 years ago. By examining the history of other organisms through glacial cycles, valuable models for evolutionary biogeography can be formulated. According to one such model, the adoption of a new refugium by a subgroup of a species may lead to important evolutionary changes.
Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia's megafauna. Our results suggest that human arrival rather than climate caused megafaunal extinction, which then triggered replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape. This ecosystem shift was as large as any effect of climate change over the last glacial cycle, and indicates the magnitude of changes that may have followed megafaunal extinction elsewhere in the world.
s335-1610-Supplement.pdf, s335-1610-Supplement1.xlsx, s335-1610-Supplement2.xlsx, s335-1610-Supplement3.xlsx, s335-1610-Supplement4.xlsx, s335-1610-Supplement5.xlsx
The present-day 238U/235U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision 238U/235U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. This data set exhibits a range in 238U/235U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional trends. Variation between comagmatic minerals suggests that 238U/235U fractionation processes operate at magmatic temperatures. A mean 238U/235U value of 137.818 ± 0.045 (2s) in zircon samples reflects the average uranium isotopic composition and variability of terrestrial zircon. This distribution is broadly representative of the average crustal and “bulk Earth” 238U/235U composition.
N. Kinoshita, M. Paul, Y. Kashiv, P. Collon, C. M. Deibel, B. DiGiovine, J. P. Greene, D. J. Henderson, C. L. Jiang, S. T. Marley, T. Nakanishi, R. C. Pardo, K. E. Rehm, D. Robertson, R. Scott, C. Schmitt, X. D. Tang, R. Vondrasek, A. Yokoyama
The extinct p-process nuclide 146Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its a-decay daughter 142Nd. Based on analyses of 146Sm/147Sm a-activity and atom ratios, we determined the half-life of 146Sm to be 68 ± 7 (1s) million years, which is shorter than the currently used value of 103 ± 5 million years. This half-life value implies a higher initial 146Sm abundance in the early solar system, (146Sm/144Sm)0 = 0.0094 ± 0.0005 (2s), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with 146Sm-142Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)0 values.
New 238U/235U ratios for uranium-bearing minerals provide a better chronometer for dating geological processes.
Nuclear accidents that lead to melting of a reactor core create heterogeneous materials containing hundreds of radionuclides, many with short half-lives. The long-lived fission products and transuranium elements within damaged fuel remain a concern for millennia. Currently, accurate fundamental models for the prediction of release rates of radionuclides from fuel, especially in contact with water, after an accident remain limited. Relatively little is known about fuel corrosion and radionuclide release under the extreme chemical, radiation, and thermal conditions during and subsequent to a nuclear accident. We review the current understanding of nuclear fuel interactions with the environment, including studies over the relatively narrow range of geochemical, hydrological, and radiation environments relevant to geological repository performance, and discuss priorities for research needed to develop future predictive models.
Pierre Deschamps, Nicolas Durand, Edouard Bard, Bruno Hamelin, Gilbert Camoin, Alexander L. Thomas, Gideon M. Henderson, Jun'ichi Okuno & Yusuke Yokoyama
Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.
The exact origin, timing and amplitude of a rapid period of sea-level rise known as meltwater pulse 1A, about 14,500 years ago, have remained unclear. An analysis of coral samples from Tahiti delivers some answers.
Contentious observations of Pleistocene shoreline features on the tectonically stable islands of Bermuda and the Bahamas have suggested that sea level about 400,000 years ago was more than 20 metres higher than it is today1-4. Geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage (MIS) 11, an unusually long interval of warmth during the ice age1-4. Previous work has advanced two divergent hypotheses for these shoreline features: first, significant melting of the East Antarctic Ice Sheet, in addition to the collapse of the West Antarctic Ice Sheet and the Greenland Ice Sheet1-3; or second, emplacement by a mega-tsunami during MIS 11 (ref. 4, 5). Here we showthat the elevations of these features are correcteddownwards by 10metres whenwe account for post-glacial crustal subsidence of these sites over the course of the anomalously long interglacial. On the basis of this correction, we estimate that eustatic sea level rose to 6-13m above the present-day value in the second half of MIS 11. This suggests that both the Greenland Ice Sheet and the West Antarctic Ice Sheet collapsed during the protracted warm period while changes in the volume of the East Antarctic Ice Sheet were relatively minor, thereby resolving the long-standing controversy over the stability of the East Antarctic Ice Sheet during MIS 11.
Across Atlantic Ice: The Origin of America's Clovis. Dennis J. Stanford & Bruce A. Bradley. Preis: EUR 26,00, Gebundene Ausgabe: 304 %
Seiten, Verlag: University of California (21. Februar 2012), Sprache: Englisch, ISBN-10: 0520227832
When originally proposed in the late 1990s, Stanford and Bradley's hypothesis linked Solutrean artifacts to those of the 13,000-year-old Clovis culture, the first clearly identified stone-tool-making tradition in the Americas. Since then, additional strong evidence for pre-Clovis tools has come to light (Science, 25 March 2011, p. 1512); most experts still think the first Americans hailed from Asia, although earlier than once thought.
Ancient DNA expert Eske Willerslev of the University of Copenhagen sides with the critics that no current evidence supports the Solutrean hypothesis. But he also agrees with Stanford and Bradley that researchers need additional older North American DNA, in particular from the much larger and more informative nuclear genome, before the controversy can be resolved. Thus down but not out, the Solutrean hypothesis lives for another day.
Free Will. Sam Harris. Free Press 96 pp. $9.99 (2012)
Neuroscientist Sam Harris, the author of the bestselling The Moral Landscape (2010), here skewers the concept of free will – that mainstay of law, policy and politics – in fewer than 100 pages. Using evidence drawn from psychology and neuroscience, Harris asserts that the course of human life is all down to luck, and that willpower is a “biological phenomenon”. We are not in charge of our own minds, he says: thought and intention simply arise. This is a tract that is sure to boldly go straight to the heart of the determinism debate.
Born Believers: The Science of Children's Religious Belief. Justin L. Barrett. Free Press 320 pp. $26.00 (2012)
Psychologist Justin Barrett says that belief is rooted not in indoctrination, but in a default setting of the infant brain. A range of findings in developmental psychology, he argues, support the theory: very young children, for instance, are aware that nature is not designed by humans; and people tend to look for unseen agents behind natural phenomena. Barrett says that the evidence points to a universal “natural religion” – but he also argues that parents must not impose belief systems on their children, and should leave the question of whether to die a believer up to their offspring.
The history of the memory sciences resembles in some respects the claims about memory made by one particular psychologist-Bartlett, whose mantra was that the fate, significance, and meaning of all psychic material was in the hands of future users.
Memory. Fragments of a Modern History. by Alison Winter. University of Chicago Press, Chicago, 2011. 329 pp. $30, £19.95. ISBN 9780226902586.
The notion that “secreted within us are perfect records of past experiences” was the very theory that Bartlett vigorously opposed-the “trace theory” of memory. Winter does a masterful job of explicating Bartlett's perspective, despite its odd placement late in the book between recovered memories and the FMSF. Regardless of this quibble, her rich account of the development of Bartlett's work, from his early fellowship dissertation studies of conventionalization to his dynamic model of memory schema, shows that it is more than an argument for the falsity of memory.
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