Samples were sawn into slabs and the central parts (4200 g) were used for bulk-rock analysis. The rocks were crushed into small fragments (50•5 cm in diameter) before being further cleaned and powdered in a corundum mill. Bulk-rock geochemical analyses were carried out at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences. Bulk-rock major element oxides were analyzed by X-ray fluorescence (XRF) with analytical uncertainties better than 3% for SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O and K 2 O, and better than 5% for TiO 2 , MnO and P 2 O 5. Trace elements were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Repeated runs give 53% RSD (relative standard deviation) for most trace elements analyzed. Fe/Mn ratios

We use the C/N ratio as a monitor of the delivery of key ingredients of life to nascent terrestrial worlds. Total elemental C and N contents, and their ratio, are examined for the interstellar medium, comets, chondritic meteorites, and terrestrial planets; we include an updated estimate for the bulk silicate Earth (C/N = 49.0 ± 9.3). Using a kinetic model of disk chemistry, and the sublimation/condensation temperatures of primitive molecules, we suggest that organic ices and macromolecular (refractory or carbonaceous dust) organic material are the likely initial C and N carriers. Chemical reactions in the disk can produce nebular C/N ratios of ∼1-12, comparable to those of comets and the low end estimated for planetesimals. An increase of the C/N ratio is traced between volatile-rich pristine bodies and larger volatile-depleted objects subjected to thermal/accretional metamorphism. The C/N ratios of the dominant materials accreted to terrestrial planets should therefore be higher than those seen in carbonaceous chondrites or comets. During planetary formation, we explore scenarios leading to further volatile loss and associated C/N variations owing to core formation and atmospheric escape. Key processes include relative enrichment of nitrogen in the atmosphere and preferential sequestration of carbon by the core. The high C/N bulk silicate Earth ratio therefore is best satisfied by accretion of thermally processed objects followed by large-scale atmospheric loss. These two effects must be more profound if volatile sequestration in the core is effective. The stochastic nature of these processes hints that the surface/atmospheric abundances of biosphereessential materials will likely be variable.terrestrial worlds | elements | interstellar medium | comets | meteorites T he development of a habitable world and a stable biosphere requires the delivery of biogenic elements of which carbon and nitrogen are crucial. Carbon is the backbone for the chemistry of life and, in the form of CO 2 , combines with water to provide the greenhouse needed for a habitable Earth. Nitrogen is a key component of DNA, RNA, and proteins, while also present as the dominant constituent of our atmosphere. The processes that supply these crucial ingredients remain poorly understood. In interstellar space, C and N are abundant, but inherently volatile and so chiefly remain in the gas. Thus, the terrestrial planets, which accrete primarily from rocks and ices, are fed from C-and N-depleted materials and are carbon and nitrogen poor compared with the nebular disk from which they descend (1, 2). The carbon and nitrogen depletion of rocky bodies is a general phenomenon, observable not just in our solar system, but also in the polluted atmospheres of white dwarf stars, which trace the composition of disrupted planetesimals (3, 4). This volatile poor state of terrestrial planets is partially imparted from the starting materials. However, further differential loss of C and N can occur due to parent body processes such as thermal metamorphism, core s...

The Golgi apparatus is the central hub for protein trafficking and glycosylation in the secretory pathway. However, how the Golgi responds to glucose deprivation is so far unknown. Here, we report that GRASP55, the Golgi stacking protein located in medial- and trans-Golgi cisternae, is O-GlcNAcylated by the O-GlcNAc transferase OGT under growth conditions. Glucose deprivation reduces GRASP55 O-GlcNAcylation. De-O-GlcNAcylated GRASP55 forms puncta outside of the Golgi area, which co-localize with autophagosomes and late endosomes/lysosomes. GRASP55 depletion reduces autophagic flux and results in autophagosome accumulation, while expression of an O-GlcNAcylation-deficient mutant of GRASP55 accelerates autophagic flux. Biochemically, GRASP55 interacts with LC3-II on the autophagosomes and LAMP2 on late endosomes/lysosomes and functions as a bridge between LC3-II and LAMP2 for autophagosome and lysosome fusion; this function is negatively regulated by GRASP55 O-GlcNAcylation. Therefore, GRASP55 senses glucose levels through O-GlcNAcylation and acts as a tether to facilitate autophagosome maturation.

Significance Seismic studies revealed that shear wave ( S wave) travels through the inner core at an anomalously low speed, thus challenging the notion of its solidity. Here we show that for the candidate inner core component Fe 7 C 3 , shear softening associated with a pressure-induced spin-pairing transition leads to exceptionally low S -wave velocity ( v S ) in its low-spin and nonmagnetic phase. An Fe 7 C 3 -dominant inner core would match seismic observations and imply a major carbon reservoir in Earth’s deepest interior.

The nature of light element(s) in the core holds key to our understanding of Earth's history of accretion and differentiation, but the core composition remains poorly constrained. Carbon has been proposed to be a major constituent of the inner core, with broad implications for the global carbon cycle, the budget of volatiles in the Earth and origin of carbon‐based life in the Solar System. However, existing estimates of the inner core's carbon content remain highly controversial because of poor constraints on the behavior of compressed iron carbides. Here we investigated the structure, elasticity, and magnetism of Eckstrom‐Adcock carbide Fe7C3up to core pressures, using synchrotron‐based single‐crystal X‐ray diffraction and Mössbauer spectroscopy techniques. We detected two discontinuities in the compression curve up to 167 gigapascals (GPa), the first of which corresponds to a magnetic collapse between 5.5 and 7.5 GPa and is attributed to a ferromagnetic to paramagnetic transition. At the second discontinuity near 53 GPa, Fe7C3softens and exhibits Invar behavior, presumably caused by a high‐spin to low‐spin transition. Considering the magneto‐elastic coupling effects, an Fe7C3‐dominant composition can match the density of the inner core, making the core potentially the largest reservoir of carbon in Earth.

Earth's earliest history was marked by accretion from protoplanetary materials and segregation of the core within about 35 m.y. (Kleine et al. 2002;Yin et al. 2002) and formation of the Moon by giant impact approximately 100 m.y. after the origin of the solar system. During this primary differentiation, all elements were distributed between the Fe-rich metallic phase and the silicate mantle according to their partition coefficients D i (D i = [i] metal /[i] silicate ). The net result is that the mantle is relatively depleted in those (siderophile) elements with high D i , which partitioned strongly into the core and enriched in lithophile elements with low D values. These qualitative observations are placed in context by the observation that Earth's mantle has strong compositional affinities with chondritic meteorites (Allègre et al 1995;McDonough and Sun 1995). Figure 1 shows the abundances of a large number of elements in silicate Earth compared to those in CI chondrites plotted against the temperature at which 50% of the element would condense from a gas of solar composition. Refractory lithophile elements (those which condense at highest temperature) are present in the mantle in approximately chondritic proportions, which implies that all refractory elements are present in bulk Earth (core plus mantle) in approximately chondritic proportions. In contrast, silicate Earth is depleted in volatile elements relative to CI chondrites with a decreasing relative abundance with decreasing condensation temperature. Siderophile elements are partitioned into the core and, in the case of refractory elements, their concentrations in the metal phase may be estimated by mass balance by assuming overall chondritic abundance in bulk Earth (McDonough 2003). In contrast, the abundances of volatile elements such as S, C, and Si in the core are more difficult to estimate because of the non-chondritic bulk Earth ratios of these elements. Nevertheless, plausible bounds may be placed on their concentrations, as discussed below. Mg SiAu Pd Rh,Pt Ru,Ir Re,Os P As Mo Ca, Ti,REE Zr Sc,Al W

No abstract

Except for the first 50-100 million years or so of the Earth's history, when most of the mantle may have been subjected to melting, the differentiation of Earth's silicate mantle has been controlled by solid-state convection. As the mantle upwells and decompresses across its solidus, it partially melts. These low-density melts rise to the surface and form the continental and oceanic crusts, driving the differentiation of the silicate part of the Earth. Because many trace elements, such as heat-producing U, Th and K, as well as the noble gases, preferentially partition into melts (here referred to as incompatible elements), melt extraction concentrates these elements into the crust (or atmosphere in the case of noble gases), where nearly half of the Earth's budget of these elements now resides. In contrast, the upper mantle, as sampled by mid-ocean ridge basalts, is highly depleted in incompatible elements, suggesting a complementary relationship with the crust. Mass balance arguments require that the other half of these incompatible elements be hidden in the Earth's interior. Hypotheses abound for the origin of this hidden reservoir. The most widely held view has been that this hidden reservoir represents primordial material never processed by melting or degassing. Here, we suggest that a necessary by-product of whole-mantle convection during the Earth's first billion years is deep and hot melting, resulting in the generation of dense liquids that crystallized and sank into the lower mantle. These sunken lithologies would have 'primordial' chemical signatures despite a non-primordial origin.