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We have determined the solubility of sulfur (S) as sulfide (S2–) for 13 different natural melt compositions at temperatures of 1473–1773 K under controlled conditions of oxygen and sulfur fugacities (fO2 and fS2, respectively). The S and major element contents of the quenched glasses were determined by electron microprobe. The sulfide capacity parameter (CS2–) was used to express S2– solubility as a function of the oxygen and sulfur fugacities according to the equation: log C S 2 - = log S melt w t % + 0.5 log f O 2 f S 2 . Sulfide capacities of silicate melts were found to increase with temperature and the FeO content of the melt. We combined our sulfide data at 1473–1773 K with (O'Neill and Mavrogenes, J Petrol 43:1049–1087, 2002) results at 1673 K, and obtained by stepwise linear regression the following equation for sulfide capacity log C S 2 - = 0.225 + 25237 X FeO + 5214 X CaO + 12705 X MnO + 19829 X K 2 O - 1109 X S i 0.5 O - 8879 / T . XMO is the mole fraction of the oxide of M on a single-oxygen basis, and T is in Kelvin. The sulfide capacity equation was combined with sulfate capacity (CS6+) data for similar compositions and at the same temperatures (Boulliung and Wood, Geochim Cosmochim Acta 336:150–164, 2022), to estimate the S redox state (S6+/S2– ratio) as a function of melt composition, temperature and oxygen fugacity. Results obtained are in good agreement with earlier measurements of S6+/S2– for basaltic and andesitic compositions. We observe a significant increase, however, relative to FMQ of the oxygen fugacity of the S2– to S6+ transition as temperature is lowered from 1773 to 1473 K. We used our results to simulate sulfur-degassing paths for basaltic compositions under various redox conditions (FMQ –2 log fO2 units to FMQ + 2). The calculations indicate that, given an initial concentration of 0.12 wt% S in an ascending melt at 250 MPa, most of the S (> 80%) will be degassed before the magma reaches 100 MPa pressure. [ABSTRACT FROM AUTHOR]

The loss of coastal marshes is a topic of great concern, because these habitats provide tangible ecosystem services and are at risk from sea-level rise and human activities. In recent years, a significant effort has gone into understanding and modeling the relationships between the biological and physical factors that contribute to marsh stability. Simulation-based process models suggest that marsh stability is the product of a complex feedback between sediment supply, flooding regime and vegetation response, resulting in elevation gains sufficient to match the combination of relative sea-level rise and losses from erosion. However, there have been few direct, empirical tests of these models, because long-term datasets that have captured sufficient numbers of marsh loss events in the context of a rigorous monitoring program are rare. We use a multi-year dataset collected by the Coastwide Reference Monitoring System that includes transitions of monitored vegetation plots to open water to build and test a predictive model of near-term marsh vulnerability. We found that despite the conclusions of previous process models, elevation change had no ability to predict the transition of vegetated marsh to open water. However, we found that the processes that drive elevation change were significant predictors of transitions. Specifically, vegetation cover in prior year, land area in the surrounding 1 km2 (an estimate of marsh fragmentation) and the interaction of tidal amplitude and position in tidal frame were all significant factors predicting marsh loss. This suggests that (1) elevation change is likely better a predictor of marsh loss at timescales longer than we consider in this study and (2) the significant predictive factors affect marsh vulnerability through pathways other than elevation change, such as resistance to erosion. In addition, we found that, while sensitivity of marsh vulnerability to the predictive factors varied spatially across coastal Louisiana, vegetation cover in prior year was the best single predictor of subsequent loss in most sites followed by changes in percent land and tidal amplitude. The model’s predicted land loss rates correlated well with land loss rates derived from satellite data, although agreement was spatially variable. These results indicate (1) monitoring the loss of small-scale vegetation plots can inform patterns of land loss at larger scales, (2) the drivers of land loss vary spatially across coastal Louisiana, and (3) relatively simple models have potential as highly informative tools for bioassessment, directing future research and management planning. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recent 142Nd isotope data indicate that the silicate Earth (its crust plus the mantle) has a samarium to neodymium elemental ratio (Sm/Nd) that is greater than that of the supposed chondritic building blocks of the planet. This elevated Sm/Nd has been ascribed either to a 'hidden' reservoir in the Earth or to loss of an early-formed terrestrial crust by impact ablation. Since removal of crust by ablation would also remove the heat-producing elements-potassium, uranium and thorium-such removal would make it extremely difficult to balance terrestrial heat production with the observed heat flow. In the 'hidden' reservoir alternative, a complementary low-Sm/Nd layer is usually considered to reside unobserved in the silicate lower mantle. We have previously shown, however, that the core is a likely reservoir for some lithophile elements such as niobium. We therefore address the question of whether core formation could have fractionated Nd from Sm and also acted as a sink for heat-producing elements. We show here that addition of a reduced Mercury-like body (or, alternatively, an enstatite-chondrite-like body) rich in sulfur to the early Earth would generate a superchondritic Sm/Nd in the mantle and an 142Nd/144Nd anomaly of approximately +14 parts per million relative to chondrite. In addition, the sulfur-rich core would partition uranium strongly and thorium slightly, supplying a substantial part of the 'missing' heat source for the geodynamo. [ABSTRACT FROM AUTHOR]

Ian Carmichael spent 45 years thinking about and working on the activities of components in silicate melts and their use to estimate physicochemical conditions at eruption and in the source regions of igneous rocks. These interests, principally in major components such as SiO, led us to think about possible ways of determining the complementary activity coefficients of trace components in silicate melts. While investigating the conditions of accretion and differentiation of the Earth, a number of authors have determined the partitioning of trace elements such as Co, Ni, Mo and W between liquid Fe metal and liquid silicate. These data have the potential to provide activity information for a large number of trace components in silicate melts. In order to turn the partitioning measurements into activities, however, we need to know the activity coefficient of FeO, γ in the silicate. We obtained γ as a function of melt composition by fitting a simple model to 83 experimental data for which the authors had measured the FeO content of the silicate melt in equilibrium with metal (Fe-bearing alloy) at known f. The compositional dependence of γ is weak, but, when calculated in the system Diopside-Anorthite-Forsterite, it decreases towards the Forsterite apex. A similar approach for Ni, for which twice as many data are available, leads to similar composition dependence of activity coefficient and confirms the suggestion that γ/γ is almost constant over a wide range of silicate melt composition. The activity coefficients for FeO were used in conjunction with measured Mo and W partitioning between Fe-rich metal and silicate melt to estimate activity coefficients for trace MoO and WO dissolved in silicate melt. When combined with data on Mo- and W-saturated silicate melts a strong dependence of activity coefficient is observed. Calculated in the system Diopside-Anorthite-Forsterite, both MoO and WO exhibit similar behaviour to FeO and NiO in that activity coefficients decrease as Forsterite content increases. The effect is much larger for Mo and W, however, γ and γ varying by factors of 20 and nearly 100, respectively, in this system. In order to illustrate the potential applications of the metal-silicate partitioning approach to determine the activity coefficients of volatile elements, we used it to determine activity coefficients of PbO, CuO and InO in a silica-saturated melt at 1,650 °C. We find values of 0.22, 3.5 and 0.02, respectively, indicating a strong dependence on cation charge. The value for CuO is in excellent agreement with experimental data of Holzheid and Lodders (Geochim Cosmochim Acta 65:1933-1951, ), which shows that the method is viable. When combined with thermodynamic data on the gas species, we find that Pb is the most volatile of the 3 elements under 'normal' terrestrial conditions of oxygen fugacity but that In should become the most volatile under strongly reducing conditions such as those of the solar nebula. The oxygen fugacity dependence of volatility has implications for the high relative abundance of In in silicate Earth. We conclude that metal-silicate partitioning experiments are a viable means for determining activities of trace components in silicate melts and are particularly useful if the metal of the element is unstable or volatile at igneous temperatures. [ABSTRACT FROM AUTHOR]

Four-field anthropology departments are no longer in a 'steady state'. Their integrity is threatened by a combination of internal and external developments. It remains to be seen whether they, in combination, are powerful enough to break the historic bonds that have united them for nearly a century. [ABSTRACT FROM AUTHOR]

Modern humans represent the only surviving species of an otherwise extinct clade of primates, the hominins. As the closest living relatives to extinct hominins, extant primates are an important source of comparative information for the reconstruction of the diets of extinct hominins. Methods such as comparative and functional morphology, finite element analysis, dental wear, dental topographic analysis, and stable isotope biogeochemistry must be validated and tested within extant populations before they can be applied to extinct taxa. Here we review how these methods have and might be used to reconstruct the diet of a particular extinct hominin, Paranthropus boisei, which has no extant analogue for its highly derived masticatory morphology. Our review emphasizes the potential and limitations of using extant primates as models for the reconstruction of extinct hominin diets. We encourage paleoanthropologists and those who study the feeding behaviors of extant primates to work together to investigate and validate methods for interpreting the diets of all extinct primates, including hominins. [ABSTRACT FROM AUTHOR]

The supraspinatus muscle is a key component of the soft tissues of the shoulder. In pronograde primates, its main function, in combination with the other rotator cuff muscles (subscapularis, infraspinatus, and teres minor), is to stabilize the glenohumeral joint, whereas in orthograde primates it functions together with the deltoid, to elevate the upper extremity in the scapular plane. To determine whether these functional differences are also reflected in the molecular biochemistry of the supraspinatus muscles involved in these different locomotor modes, we used real-time polymerase chain reaction (RT-PCR) to analyze the expression of the myosin heavy chain (MHC) isoforms in supraspinatus muscles from modern humans and 12 species of pronograde and orthograde primates. The MHC expression pattern in the supraspinatus muscle of pronograde primates was consistent with its function as a tonic and postural muscle, whereas the MHC expression pattern observed in the supraspinatus muscle of nonhuman orthograde primates was that of a muscle that emphasizes speed, strength, and less resistance to fatigue. These findings are consistent with the role of the supraspinatus in the posture and locomotor modes of these groups of nonhuman primates. The humans included in the study had an expression pattern similar to that of the nonhuman orthograde primates. In conclusion, molecular analysis of skeletal muscles via RT-PCR can contribute to a better understanding of the morphological and functional characteristics of the primate musculoskeletal system. [ABSTRACT FROM AUTHOR]

Clinopyroxene-melt trace element partitioning experiments were carried out in the system NaO-CaO-MgO-AlO-SiO at pressures of 1, 2.3 and 3 GPa and temperatures of 1508 to 1811 K, to investigate the effects of temperature ( T), pressure ( P) and composition ( X) on partition coefficients. Of particular interest were elements entering the octahedral M1-site. Ion probe analyses of run products produced crystal-melt partition coefficients ( D) for 16 elements (Na, Ca, Al, Cl, Sc, Ti, Fe, Zr, In, La, Ce, Nd, Sm, Ho, Yb and Hf). With the exception of D, partition coefficients for all elements studied decrease with increased P and T, despite the concomitant increase in the Al content of the T-site. Fitting partition coefficients for isovalent series of cations to the elastic strain model of Blundy and Wood () produced values for the site radius ( r), effective elastic modulus ( E) and strain-free partition coefficient ( D). At each pressure, E values for the M1 and M2-sites increase with increasing Al concentration in the T-site $$ \left( {X_{\text{Al}}^{T} } \right) $$. For a given bulk composition, E values decrease with increased T. The decrease in E with increasing T accounts for the remarkable constancy of the degree of fractionation between chemically similar elements, e.g. $$ D\left( {{\frac{\text{Zr}}{\text{Hf}}}} \right) $$, over the range of pressures studied here. $$ E_{{{\text{M}}1}}^{4 + } $$ for our experiments is found to be higher than predicted by the Hazen and Finger () relationship between elastic moduli and interatomic distance. This is explained by deformation of the M1-site polyhedron leading to relative displacement and kinking of the clinopyroxene T-site chains. We developed expressions for $$ E_{{{\text{M}}1}}^{4 + } $$, $$ r_{{0,{\text{M}}1}}^{4 + } $$, D and D as functions of P, T and composition. We show the feasibility of using calculated D values in the prediction of D and D. Scandium and Ti partition coefficients were modelled based on the thermodynamic description for the crystal-melt exchange reaction and in terms of the energetics of the different charge-imbalanced configurations produced by insertion of a heterovalent trace cation. The resulting equations produce values of D and D that are within a factor of 2 of other experimentally determined values. Fits of the equations along the lherzolite solidus show that D remains compatible in clinopyroxene at high pressure and that ratios of Zr/Hf and Ti/Eu should vary subtly with the pressure at which melting occurred. [ABSTRACT FROM AUTHOR]

The relationships among the living apes and modern humans have effectively been resolved, but it is much more difficult to locate fossil apes on the tree of life because shared skeletal morphology does not always mean shared recent evolutionary history. Sorting fossil taxa into those that belong on the branch of the tree of life that leads to modern humans from those that belong on other closely related branches is a considerable challenge. [ABSTRACT FROM AUTHOR]

The meaning of the age of the Earth defined by lead isotopes has long been unclear. Recently it has been proposed that the age of the Earth deduced from lead isotopes reflects volatile loss to space at the time of the Moon-forming giant impact rather than partitioning into metallic liquids during protracted core formation. Here we show that lead partitioning into liquid iron depends strongly on carbon content and that, given a content of ∼0.2% carbon, experimental and isotopic data both provide evidence of strong partitioning of lead into the core throughout the Earth’s accretion. Earlier conclusions that lead is weakly partitioned into iron arose from the use of carbon-saturated (about 5% C) iron alloys. The lead isotopic age of the Earth is therefore consistent with partitioning into the core and with no significant late losses of moderately volatile elements to space during the giant impact. [ABSTRACT FROM AUTHOR]

The article focuses on the discovery of a complete 3.3-million-year-old skeleton of a three-year-old Australopithecus afarensis female in Dikika, Ethiopia by Zeresenay Alemseged. There is controversy regarding the posture and locomotion of A. afarensis. Although some parts of the specimen are missing, the preserved parts include the face, the brain case and the base of the cranium.

The Earth took 30–40 million years to accrete from smaller ‘planetesimals’. Many of these planetesimals had metallic iron cores and during growth of the Earth this metal re-equilibrated with the Earth's silicate mantle, extracting siderophile (‘iron-loving’) elements into the Earth's iron-rich core. The current composition of the mantle indicates that much of the re-equilibration took place in a deep (> 400 km) molten silicate layer, or ‘magma ocean’, and that conditions became more oxidizing with time as the Earth grew. The high-pressure nature of the core-forming process led to the Earth's core being richer in low-atomic-number elements, notably silicon and possibly oxygen, than the cores of the smaller planetesimal building blocks. [ABSTRACT FROM AUTHOR]

Kelvin calculated the age of the Earth to be about 24 million years by assuming conductive cooling from being fully molten to its current state. Although simplistic, his result is interesting in the context of the dramatic cooling that took place after the putative Moon-forming giant impact, which contributed the final ∼10 per cent of the Earth's mass. The rate of accretion and core segregation on Earth as deduced from the U–Pb system is much slower than that obtained from Hf–W systematics, and implies substantial accretion after the Moon-forming impact, which occurred 45 ± 5 Myr after the beginning of the Solar System. Here we propose an explanation for the two timescales. We suggest that the Hf–W timescale reflects the principal phase of core-formation before the giant impact. Crystallization of silicate perovskite in the lower mantle during this phase produced Fe3+, which was released during the giant impact, and this oxidation resulted in late segregation of sulphur-rich metal into which Pb dissolved readily, setting the younger U–Pb age of the Earth. Separation of the latter metal then occurred 30 ± 10 Myr after the Moon-forming impact. Over this time span, in surprising agreement with Kelvin's result, the Earth cooled by about 4,000 K in returning from a fully molten to a partially crystalline state. [ABSTRACT FROM AUTHOR]

Calculations of the energetics of terrestrial accretion indicate that the Earth was extensively molten in its early history. Examination of early Archaean rocks from West Greenland (3.6–3.8 Gyr old) using short-lived 146Sm–142Nd chronometry indicates that an episode of mantle differentiation took place close to the end of accretion (4.46 ± 0.11 Gyr ago). This has produced a chemically depleted mantle with an Sm/Nd ratio higher than the chondritic value. In contrast, application of 176Lu–176Hf systematics to 3.6–3.8-Gyr-old zircons from West Greenland indicates derivation from a mantle source with a chondritic Lu/Hf ratio. Although an early Sm/Nd fractionation could be explained by basaltic crust formation, magma ocean crystallization or formation of continental crust, the absence of coeval Lu/Hf fractionation is in sharp contrast with the well-known covariant behaviour of Sm/Nd and Lu/Hf ratios in crustal formation processes. Here we show using mineral–melt partitioning data for high-pressure mantle minerals that the observed Nd and Hf signatures could have been produced by segregation of melt from a crystallizing magma ocean at upper-mantle pressures early in Earth's history. This residual melt would have risen buoyantly and ultimately formed the earliest terrestrial protocrust. [ABSTRACT FROM AUTHOR]

High-pressure melting experiments were performed at ~26 GPa and ~2,200-2,400°C on synthetic peridotite compositions with varying FeO and Al2O3 contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of MgPv followed by MgPv + Fp observed in the chondritic composition. The difference in crystallisation sequence is a consequence of the different bulk Mg/Si ratios. MgPv/melt partition coefficients for major, minor and trace elements were determined by electron microprobe and secondary ion mass spectrometry. Partition coefficients of tri- and tetravalent elements increase with increasing Al concentration in MgPv. A lattice strain model indicates that Al3+ substitutes predominantly onto the Si-site in MgPv, whereas most elements substitute onto the Mg-site, which is consistent with a charge-compensating coupled substitution mechanism. MgPv/melt partition coefficients for Mg (DMg) and Si (DSi) are related to the melt Mg/Si ratio such thatDSi becomes lower thanDMg at low Mg/Si melt ratios. We use a crystal fractionation model, based on upper mantle refractory lithophile element ratios, to constrain the amount of MgPv and Ca-silicate perovskite (CaPv) that could have fractionated during a Hadean magma ocean event and could still be present as a chemically distinct heterogeneity in the lower mantle today. We show that a fractionated crystal pile composed of 96% MgPv and 4% CaPv could comprise up to 13 wt% of the entire mantle. [ABSTRACT FROM AUTHOR]

We have determined the partition coefficients of a large number of trace elements between CaTiO3 perovskite and anhydrous silicate melts at atmospheric pressure and 3 GPa. Determination of the concentration limits of Henry’s law behaviour in the CaO-Al2O3-SiO2-TiO2 system reveals that the incorporation of rare earth elements (REE) and tetravalent large ion lithophile elements (LILE4+ such as U and Th) at the Ca-site of CaTiO3 perovskite occurs with charge compensation through Ca-vacancy formation rather than by coupled substitution of Al for Ti. When melt composition is varied, we find that partition coefficients for REE and Th are strong functions of the CaO content of the melt. The observed trends are in excellent agreement with those predicted from the Ca-vacancy model. Given that they adopt the same crystal structure and have similar trace element partitioning behaviour, CaTiO3 perovskite and the deep mantle phase CaSiO3 perovskite can be considered analogous to one another. When the analogy is pursued in detail, we find that partitioning into both phases follows the composition-dependence predicted by the Ca-vacancy model. Thus, substitution of REE, U4+ and Th into CaSiO3 in the lower mantle also occurs with Ca-vacancy formation to balance charge. Furthermore when 2+, 3+ and 4+ partition coefficients for both phases are plotted as functions of CaO melt content, the trends for CaSiO3 and CaTiO3 appear to be continuous. This surprising result means that partitioning into Ca-perovskite is independent of pressure and temperature and also of whether or not the host is CaSiO3 or CaTiO3. One implication is that CaSiO3 crystallising from a peridotitic magma ocean may have partition coefficients for Th and U up to about 400. Crystallisation and sequestration of as little as 0.25 volume% of this phase in the lower mantle early in earth history would make a significant contribution to current mantle heat production. [ABSTRACT FROM AUTHOR]

Presents a predictive model for the partitioning of magnesium and a range of trivalent trace elements between garnet and anhydrous silicate melt. Information on the partial melting in the Earth's mantle; Approaches in acquiring a framework of partitioning data relevant to mantle melting; Component found in natural magmatic garnets.

Summarizes the data relating to the structure and composition of the Earth's mantle with an emphasis on observations in favor of, or against chemical layering. Mantle structure; Phase transformations; Seismological constraints; Heat flow and geochemistry.

Presents a systematic attempt to reconstruct the evolutionary history of the bipedalism of modern humans. Locomotor behavior of early hominids; Examination of the vestibular system of living primates and early hominids; Cranial semicircular canals.

Describes the the partitioning of rare earth elements between clinopyroxene and anhydrous silicate by using a quantitative model. Background information on the study; Information on the theoretical development; Information on a melt model.

Discusses the Taung skull discovered by Raymond Dart in Africa and its connection with the diversity in the structure of early hominids. Comparison of the Taung skull and the fossil cranium found by Michel Brunet and his colleagues; Description of the skeletal structure of the early hominids; Chart showing the evolution of ape-like creatures to human.

Presents a model for predicting crystal/melt partition coefficients. Study of partitioning of 15 elements between silicate minerals and their coexisting melts; Critical role of size and elasticity of crystal lattice sites.