Search

illus

The article focuses on the experiences of Wilhelm Rahn, a German prisoners of war (POW) in Canada during World War II, as recounted in his rare memoir. Topics include Rahn's capture, his time in British military hospitals, the Canadian treatment of German prisoners of war, and the challenges faced by the POWs, including escape attempts and the impact of war news on their morale.

We have performed experiments at 1.5 GPa and 1400 °C on 25 different bulk compositions to determine the effects of major element compositions on the Cl contents of silicate melts at known fugacities of Cl2and O2. The experimental method involved mixing a “sliding” Cl buffer, a mixture of AgCl, AgI, and Ag with the silicate bulk composition and performing the experiment in a graphite capsule together with a source of CO2(AgCO3). The graphite capsules were sealed inside welded Pt tubes to maintain a CO2-CO atmosphere with oxygen fugacity fixed at the C-CO-CO2(CCO) buffer. During the experiment, the Cl buffer segregates leaving a Cl-bearing melt, which quenches to a glass. We used the results to define chloride capacity CClfor each melt at the pressure and temperature of the experiment:

We performed a series of experiments at 1 atm pressure and temperatures of 1300–1500 °C to determine the effect of oxygen fugacity on the oxidation state of Fe in a synthetic martian basalt. Ferric-ferrous ratios were determined on the quenched glasses using Mössbauer spectroscopy. Following the conventional doublet assignments in the spectrum, we obtain a Fe3+/ΣFe value of 0.19 at 1450 °C and an oxygen fugacity corresponding to the QFM buffer. If we apply the Berry et al. (2018)assignments the calculated Fe3+/ΣFe drops to 0.09, and the slope of log(XFemeltO1.5/XFemelt O) vs. log( fO2) changes from 0.18 to 0.26.

Econometric predictions of the success or failure of sanctions against a nation need to be modified with political considerations. The models proposed by Gary Hufbauer and Kimberly Ann Elliott, and by San Ling Lam, were mistakenly used by Hufbauer and Elliott in 1990 to suggest sanctions would drive Iraq out of Kuwait. These models can be made more accurate by the inclusion of factors such as the regime's internal vulnerability and whether the goals of the sanctions are of ultimate importance to the boycotted nation. A model incorporating these factors does not predict success of sanctions in the Iraqi question.

The article focuses on the evolution of Homo erectus alongside the evolution of other hominin species. Topics include the how paleoanthropologists use fossil remains to determine human evolution, the evolution of Neanderthals, and discoveries of Australopithecus remains. Information is provided on researcher Charles Darwin's theory of evolution.

These three books consider the nature and evolutionary context of the individual and collective behavior of modern humans. Moffett’s The Human Swarm and Christakis’ Blue­print focus on the “big picture.” What, if anything, is distinctive about the ways groups of modern humans behave? What do modern human societies have in common that distin­guishes them from aggregations of non-human organisms? Wrangham’s The Goodness Par­adox focuses more narrowly on aggression, and the enigma that modern humans seem to be individually relatively docile, but collectively capable of planning and executing highly aggressive activities. I was intrigued and educated by all three books.

The article focuses on Paranthropus boisei, which belonged to the hominins that lived in East African and was believed to be an extinct but close relative of modern humans. Topics discussed include its distinctive physical features that included a smaller brain and a massive set of molar and premolar teeth and additional evidence of the hominin from East Africa, particularly in Koobi Fora in Kenya.

Focuses on the skull unearthed in Djurab Desert in Chad. Significance of the picture on the idea of human evolution; Complexity of the evolutionary history based on research on fossils; Contribution of molecular biology in confirming that humans are merely a rather peculiar African ape.

As part of a project to investigate the volatilities of so-called “moderately volatile elements” such as Zn, In, Tl, Ga, Ag, Sb, Pb, and Cl during planetary formation, we began by re-calculating the condensation temperatures of these elements from a solar gas at 10-4bar. Our calculations highlighted three areas where currently available estimates of condensation temperature could be improved. One of these is the nature of mixing behavior of many important trace elements when dissolved in major condensates such as silicates, Fe-rich metals, and sulfides. Nonideal solution of the trace elements can alter (generally lower) condensation temperatures by up to 500 K. Second, recent measurements of the halogen contents of CI chondrites (Clay et al. 2017) indicate that the solar system abundance of chlorine is significantly overestimated, and this affects the stabilities of gaseous complexes of many elements of interest. Finally, we have attempted to improve on previous estimates of the free energies of chlorine-bearing solids since the temperature of chlorine condensation has an important control on the condensation temperatures of many trace elements. Our result for the 50% condensation temperature of chlorine, 472 K is nearly 500 K lower than the result of Lodders (2003), and this means that the HCl content of the solar gas at temperatures <900 K is higher than previously estimated.

The oxidation state of iron in Earth’s mantle is well known to depths of approximately 200 km, but has not been characterized in samples from the lowermost upper mantle (200–410 km depth) or the transition zone (410–660 km depth). Natural samples from the deep (>200 km) mantle are extremely rare, and are usually only found as inclusions in diamonds. Here we use synchrotron Mössbauer source spectroscopy complemented by single-crystal X-ray diffraction to measure the oxidation state of Fe in inclusions of ultra-high pressure majoritic garnet in diamond. The garnets show a pronounced increase in oxidation state with depth, with Fe3+/(Fe3++ Fe2+) increasing from 0.08 at approximately 240 km depth to 0.30 at approximately 500 km depth. The latter majorites, which come from pyroxenitic bulk compositions, are twice as rich in Fe3+as the most oxidized garnets from the shallow mantle. Corresponding oxygen fugacities are above the upper stability limit of Fe metal. This implies that the increase in oxidation state is unconnected to disproportionation of Fe2+to Fe3+plus Fe0. Instead, the Fe3+increase with depth is consistent with the hypothesis that carbonated fluids or melts are the oxidizing agents responsible for the high Fe3+contents of the inclusions. The lowermost mantle and transition zone are increasingly oxidized at depth, according to analyses of the oxidation state of iron in majoritic garnet inclusions from deep diamonds.

The silicate Earth is strongly depleted in moderately volatile elements (such as lead, zinc, indium and alkali elements) relative to CI chondrites, the meteorites that compositionally most closely resemble the Sun. This depletion may be explained qualitatively by accretion of 10 to 20 per cent of a volatile-rich body to a reduced volatile-free proto-Earth, followed by partial extraction of some elements to the core. However, there are several unanswered questions regarding the sources of Earth’s volatiles, notably the overabundance of indium in the silicate Earth. Here we examine the melting processes that occurred during accretion on Earth and precursor bodies and report vaporization experiments under conditions of fixed temperature and oxygen fugacity. We find that the pattern of volatile element depletion in the silicate Earth is consistent with partial melting and vaporization rather than with simple accretion of a volatile-rich chondrite-like body. We argue that melting and vaporization on precursor bodies and possibly during the giant Moon-forming impact were responsible for establishing the observed abundances of moderately volatile elements in Earth.

Subduction of oceanic crust generates chemical and lithological heterogeneities in the mantle. An outstanding question is the extent to which these heterogeneities contribute to subsequent magmas generated by mantle melting, but the answer differs depending on the geochemical behaviour of the elements under investigation: analyses of incompatible elements (those that preferentially concentrate into silicate melts) suggest that recycled oceanic crust is an important contributor, whereas analyses of compatible elements (those that concentrate in crystalline residues) generally suggest it is not. Recently, however, the concentrations of Mn and Ni—two elements of varying compatibility—in early-crystallizing olivines, have been used to infer that erupted magmas are mixtures of partial melts of olivine-rich mantle rocks (that is, peridotite) and of metasomatic pyroxene-rich mantle rocks (that is, pyroxenite) formed by interaction between partial melts of recycled oceanic crust and peridotite. Here, we test whether melting of peridotite alone can explain the observed trend in olivine compositions by combining new experimental data on the partitioning of Mn between olivine and silicate melt under conditions relevant to basalt petrogenesis with earlier results on Ni partitioning. We show that the observed olivine compositions are consistent with melts of fertile peridotite at various pressures—importantly, melts from metasomatic pyroxenites are not required. Thus, although recycled materials may well be present in the mantle source regions of some basalts, the Mn and Ni data can be explained without such a contribution. Furthermore, the success of modelling the Mn–Ni contents of olivine phenocrysts as low-pressure crystallization products of partial melts of peridotite over a range of pressures implies a simple new approach for constraining depths of mantle melting.

The extent to which sulfur dissolves in silicate melts saturated in an immiscible sulfide phase is a fundamental question in igneous petrology and plays a primary role in the generation of magmatic ore deposits, volcanic degassing, and planetary differentiation. In igneous systems, sulfide melts can be described as FeS-NiS-CuS0.5solutions with Fe/(Fe+Ni+Cu) significantly less than 1. Despite the presence of Ni and Cu in the sulfide, however, most experimental studies to date have concentrated on the effects of silicate melt composition on sulfur solubility and have used essentially pure FeS as the sulfide liquid.

We have developed a method for the manufacture of polycrystalline olivine capsules, suitable as containers for olivine-saturated melts in near-liquidus experiments. The aim was to avoid some of the problems found in 1-atm gas-mixing experiments, notably iron loss from silicate melts to Pt wire loops and reaction between noble metal loops and sulfide liquids. Use of olivine capsules of fixed Mg/Fe enables the Mg# of the coexisting melt to be controlled and doping of the capsule with minor elements of interest enables partition coefficients to be determined at measureable concentrations. Capsules with olivine compositions ranging from Fo.70 to Fo.90 have been manufactured and found to remain impermeable to basaltic melts for extended periods. In the case of magnesian compositions (~Fo90), we found that several cycles of heating and cooling from (1250 to 1550 °C) were needed to enhance grain growth and reduce permeability to an acceptable level. In contrast, our iron-rich composition (Fo70) functioned well after a single cycle of heating from 800 to 1350 °C.

Sulfides, although modally of low abundance in most igneous rocks, have strong influences on the geochemical behavior of many elements including Pb, Cu, Ni, and the PGEs. In a recent paper, we demonstrated a simple relationship between the sulfide-silicate partition coefficients DMsulf/silof such elements and the FeO content of the coexisting silicate me lt (Kiseeva and Wood 2013).

Magmas erupted at convergent margins consist of components from both mantle wedge and subducted slab. In an effort to quantify the relative contributions of these sources, we have determined 19 trace element partition coefficients (D values) for orthopyroxene and clinopyroxene, in equilibrium with spinel and hydrous high-MgO melt under conditions appropriate to melting in the mantle wedge, i.e., 1.3 GPa, 1245 °C, and fO2of NNO + 1. All trace elements are more incompatible in clinopyroxene during hydrous melting than during anhydrous melting of fertile and depleted peridotite. Orthopyroxene D values are relatively insensitive to pressure, temperature, and phase composition. The new D values are used to calculate the trace-element composition of the mantle wedge, which produced primitive South Sandwich Islands and St. Vincent (Lesser Antilles) arc basalts. Both sources correspond to previously depleted mantle that has been enriched in LILEs and LREEs by slab-derived fluids. In the case of the South Sandwich Islands, the calculated source is in very close agreement with dredged fore-arc lherzolites. Our partitioning data confirm that hydrous melting of wedge peridotite itself cannot produce the characteristic enrichments of LILEs over REEs and HFSEs. Our estimates of the slab component in South Sandwich Islands and St. Vincent are consistent with estimates from other arcs, derived by alternative methods.

On 16 and 17 January 2002 The Royal Society held a meeting to discuss one of the most contentious issues in the Earth sciences, which has generated heated debate between scientists studying the Earth's interior for the last 20 years or so. In its simplest and earliest form the debate centred on whether the Earth's upper and lower mantles are mixing. Several compelling geochemical arguments required (at least) two distinct mantle reservoirs that have preserved chemical heterogeneity for billions of years. The boundary between the two reservoirs has traditionally been placed at 670 km from the Earth's surface, the depth where the major phase transition of ringwoodite to perovskite and magnesiowustite may act to impede flow. Recent seismological studies, however, provide what seems to be overwhelming evidence that some subducting slabs do penetrate deep into the lower mantle (i.e. deeper than 670 km) and thereby directly contradict the model of geochemically isolated upper and lower mantles. This evidence seems so strong that, in fact, nobody at this Discussion Meeting seriously proposed that the simple model of separately convecting isolated upper and lower mantles is appropriate for today's Earth (although Professor McKenzie, during a discussion period, did give a word of warning that the tomographic images only show seismically fast areas: they do not in themselves give direct evidence for mass transport). Although the simple model of two–layered convection appears (for the moment at least) to be out of favour, many of the arguments that supported it are still difficult for a whole–mantle–convection model to explain. Plenty of exciting alternative scenarios were presented at the meeting.

Early hominid masticatory characters are widely considered to be more prone to homoplasy than characters from other regions of the early hominid skull and therefore less reliable for phylogenetic reconstruction. This hypothesis has important implications for current reconstructions of early hominid phylogeny, but it has never been tested. In this paper we evaluate the likely veracity of the hypothesis using craniometric data from extant primate groups for which reliable consensus molecular phylogenies are available.

One of the distinguishing features of Homo sapiensis its absolutely and relatively large brain. This feature is also seen in less extreme form in some fossil Homospecies. However, are increases in brain size during the Plio-Pleistocene only seen in Homo, and is brain enlargement among Plio-Pleistocene primates confined to hominins? This study examines evidence for changes in brain size for species and lineage samples of three synchronic East African fossil primate groups, the two hominin genera Homoand Paranthropus, and the cercopithecoid genusTheropithecus. Hominin endocranial capacity data were taken from the literature, but it was necessary to develop an indirect method for estimating the endocranial volume of Theropithecus. Bivariate and multivariate regression equations relating measured endocranial volume to three external cranial dimensions were developed from a large (ca.340) sample of modern African cercopithecoids. These equations were used to estimate the endocranial volumes of 20 Theropithecusspecimens from the African Plio-Pleistocene. Spearman's rho and the Hubert nonparametric test were used to search for evidence of temporal trends in both the hominin and Theropithecusdata. Endocranial volume apparently increased over time in bothHomoand Paranthropus boisei, but there was no evidence for temporal trends in the endocranial volume ofTheropithecus. Thus, hypotheses which suggest a mix of environmental, social, dietary, or other factors as catalysts for increasing brain in Plio-Pleistocene primates must accommodate evidence of brain enlargement in both HomoandParanthropus, and explain why this phenomenon appears to be restricted to hominins.

We rely on fossils for the interpretation of more than 95% of our evolutionary history. Fieldwork resulting in the recovery of fresh fossil evidence is an important component of reconstructing human evolutionary history, but advances can also be made by extracting additional evidence for the existing fossil record, and by improving the methods used to interpret the fossil evidence. This review shows how information from imaging and dental microstructure has contributed to improving our understanding of the hominin fossil record. It also surveys recent advances in the use of the fossil record for phylogenetic inference.

This review begins by setting out the context and the scope of human evolution. Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so‐called ‘common hominin ancestor’, and its only extant member is Homo sapiens. This clade contains all the species more closely‐related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini. The rest of the review sets out the formal nomenclature, history of discovery, and information about the characteristic morphology, and its behavioural implications, of the species presently included in the human clade. The taxa are considered within their assigned genera, beginning with the most primitive and finishing with Homo. Within genera, species are presented in order of geological age. The entries conclude with a list of the more important items of fossil evidence, and a summary of relevant taxonomic issues.

Since its introduction in the 18th century, the genus Homohas undergone a number of reinterpretations, all of which have served to make it a more inclusive taxon. In this paper, we trace this trend towards greater inclusiveness, and explain how it has affected the way Homois defined. We then demonstrate that the current criteria for identifying species of Homoare difficult, if not impossible, to operate using paleoanthropological evidence. We discuss alternative, verifiable, criteria, and show that when these new criteria are applied to Homo, two species, Homo habilisand Homo rudolfensis,fail to meet them. We contend that the lowest boundary of Homoshould be redrawn so that the earliest species in the genus is Homo ergaster,or early African Homo erectus.The appearance of this species at around 1.9 Myr appears to mark a distinct shift in hominin adaptive strategy involving morphological and behavioral innovations.

DNA sequences for the mitochondrial cytochromebgene from the four extant gibbon subgenera are described. The data confirm that the gibbon subgenera evolved from a common hylobatid ancestor and suggest that they diverged from each other after the divergence of the extant African great ape species. The cytochromebgene does not resolve the evolutionary relationships between the gibbon subgenera themselves.

Since its introduction in the 18th century, the genus Homo has undergone a number of reinterpretations, all of which have served to make it a more inclusive taxon. In this paper, we trace this trend towards greater inclusiveness, and explain how it has affected the way Homo is defined. We then demonstrate that the current criteria for identifying species of Homo are difficult, if not impossible, to operate using paleoanthropological evidence. We discuss alternative, verifiable, criteria, and show that when these new criteria are applied to Homo, two species, Homo habilis and Homo rudolfensis, fail to meet them. We contend that the lowest boundary of Homo should be redrawn so that the earliest species in the genus is Homo ergaster, or early African Homo erectus. The appearance of this species at around 1.9 Myr appears to mark a distinct shift in hominin adaptive strategy involving morphological and behavioral innovations.