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Full chemical equilibrium calculations of the sequence of condensation of the elements from cosmic gases made by total vaporization of dust-enriched systems were performed to investigate the oxidation state of the resulting condensates. Computations included 23 elements and 374 gas species over a range of -3=log10(total P) to -6 bar and for enrichments to 1000x in dust of C1 chondritic composition relative to a system of solar composition. Because liquids are stable condensates in these systems, the MELTS non-ideal solution model for silicate liquids was used. Condensation at logP=-3 bar and dust enrichments of 100x, 500x and 1000x occurs at oxygen fugacities of IW-3.1, IW-1.7 and IW-1.2, respectively, and, at the temperature of cessation of direct condensation of olivine from the vapor, yields X(fayalite) of 0.019, 0.088 and 0.164, respectively. Silicate liquid is a stable condensate at dust enrichments >~12.5x at logP=-3. At 1000x, the Na and K oxide contents of the last liquid reach 10.1 and 1.3 wt%, respectively, at logP=-3 bar. At logP=-3 bar, iron sulfide liquids are stable condensates at dust enrichments at least as low as 500x, and the predicted distribution of Fe between metal, silicate and sulfide at 1310K and a dust enrichment of 560x matches that found in H chondrites, and at 1330K and 675x matches that of L chondrites prior to metal loss. With some exceptions, many chondrule glass compositions fall along bulk composition trajectories for liquids in equilibrium with cosmic gases at logP=-3 bar and dust enrichments between 600x and 1000x. If these chondrules formed by secondary melting of mixtures of condensates that formed at different T, nebular regions with characteristics such as these would have been necessary to prevent loss of Na by evaporation and FeO by reduction from the liquid precursors, assuming that liquids and gas were hot for enough time to have equilibrated., 58 pages, 19 figures, 8 tables

Rabbi Norman Lamm, who assumed the presidency of Yeshiva University in 1976, sought to clarify the mission of the institution by using as its tagline the phrase Torah U'’Madda–denoting the dual aim of providing traditional Jewish study (Torah) along with a standard college curriculum (Madda, meaning knowledge). It would replace the word “Synthesis,” which generations of students, including Lamm himself, had found vague and confusing. Lamm launched what he called the Torah U'Madda Project, which ultimately included a campus lecture series, an annual journal, and a book entitled: Torah Umadda: The Encounter of Religious Learning and Worldly Knowledge in the Jewish Tradition. While denying any intention to construct a hard-and-fast institutional philosophy on how to integrate Orthodox Judaism and secular higher education, Lamm insisted that serious exposure to both Torah knowledge and the arts and sciences fulfilled the Torah's mandate to understand and appreciate all aspects of God's world. Lamm's initiative failed, however, because economic conditions induced many students to forsake the liberal arts for vocational and pre-professional courses, and the trend to the right in American Orthodoxy–expressed by rabbis at Yeshiva itself and abetted by the year or more spent at Israeli yeshivot before college–stressed single–minded concentration on Torah study and justified secular education only for the purpose of making a living.

The compositions of the first solar system solids were shaped by nonequilibrium condensation and evaporation., Equilibrium condensation of solar gas is often invoked to explain the abundance of refractory elements in planets and meteorites. This is partly motivated, by the observation that the depletions in both the least and most refractory rare earth elements (REEs) in meteoritic group II calcium-aluminum–rich inclusions (CAIs) can be reproduced by thermodynamic models of solar nebula condensation. We measured the isotopic compositions of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb in eight CAIs to test this scenario. Contrary to expectation for equilibrium condensation, we find light isotope enrichment for the most refractory REEs and more subdued isotopic variations for the least refractory REEs. This suggests that group II CAIs formed by a two-stage process involving fast evaporation of preexisting materials, followed by near-equilibrium recondensation. The calculated time scales are consistent with heating in events akin to FU Orionis– or EX Lupi–type outbursts of eruptive pre–main-sequence stars.

Accepted: 2017-05-26, 資料番号: SA1170244000

One way to better understand processes related to chondrite metamorphism is to evaluate changes in chondrite features as a function of petrologic type. Toward this end the valence and coordination of Ti in olivine and pyroxene in suites of ordinary (H, L, and LL) and enstatite (EH and EL) chondrites of types 3 through 6 have been determined with XANES spectroscopy. Trivalent Ti, typically 10–40% of the Ti in the analytical volumes, was found in ordinary chondrites of all types, despite the stability of oxidized iron in the samples. Average valences and the proportions of Ti that are in tetrahedral coordination generally decrease with increasing grade between types 3.0 and 3.5, increase from 3.5 to 4, and then level off. These trends are consistent with previous studies of chondrite oxidation states using other methods, except here the onset of oxidation is observed at a lower type, ∼3.5, than previously indicated (4). These results are also consistent with previous suggestions that oxidation of higher-grade ordinary chondrite samples involved exposure to aqueous fluids from melting of accreted ice. In the enstatite chondrites, typically 20–90% of the Ti is trivalent Ti, so it is reduced compared to Ti in the ordinary chondrites. Valence decreases slightly from petrologic type 3 to 4 and increases from 4 to 6, but no increases in tetrahedral coordination with petrologic type are observed, indicating a redox environment or process distinct from that of ordinary chondrite metamorphism. The presence of Ti4+ in the E chondrites supports previous suggestions that they formed from oxidized precursors that underwent reduction. Unlike ordinary chondrites, enstatite chondrites are thought to have been derived from a body or bodies that did not accrete ice, which could account for their different valence-coordination-petrologic type relationships. The hypothesis, based on observations of unmetamorphosed chondrules and supported by laboratory experiments, that equilibration of Ti valence is sluggish compared to that of Fe could account for the coexistence of reduced Ti and oxidized Fe seen in chondrites of all petrologic types.

A coordinated, electron-backscatter-diffraction (EBSD) and transmission electron microscope (TEM) study was undertaken to obtain information on the origin of rims on refractory inclusions in the Allende and Axtell CV3 chondrites. These measurements were supported by theoretical modeling using density functional theory. Crystal-orientation analysis of Wark-Lovering rims via EBSD revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions. An epitaxial relationship between grains within the diopside and anorthite rim layers was observed in Allende. TEM examination of the rims of both samples also revealed oriented crystals at depth. The microstructural data on the rims suggest that grain clusters grew in the form of three-dimensional islands. Density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature. The results point toward condensation as the mode of origin for the rims studied here.

The degree to which dust enrichment enhances the oxygen fugacity (fO2) of a system otherwise solar in composition depends on the dust composition. Equilibrium calculations were performed at 10−3 bar in systems enriched by a factor of 104 in two fundamentally different types of dust to investigate the iron oxidation state in both cases. One type of dust, called SC for solar condensate, stopped equilibrating with solar gas at too high a temperature for FeO or condensed water to be stabilized in any form, and thus has the composition expected of a nebular condensate. The other has CI chondrite composition, appropriate for a parent body that accreted from SC dust and low-temperature ice. Upon total vaporization at 2300 K, both systems have high fO2, >IW. In the SC dust-enriched system, FeO of the bulk silicate reaches ~10 wt% at 1970 K but decreases to

The impact hypothesis for the origin of CB chondrites was tested by performing equilibrium condensation calculations in systems composed of vaporized mixtures of projectile and target materials. When one of the impacting bodies is composed of the metal from CR chondrites and the other is an H chondrite, good agreement can be found between calculated and observed compositions of unzoned metal grains in CB chondrites but the path of composition variation of the silicate condensate computed for the same conditions that reproduce the metal grain compositions does not pass through the measured compositions of barred olivine (BO) or cryptocrystalline (CC) chondrules in the CBs. The discrepancy between measured chondrule compositions and those of calculated silicates is not reduced when diogenite, eucrite or howardite compositions are substituted for H chondrite as the silicate-rich impacting body. If, however, a CR chondrite body is differentiated into core, a relatively CaO-, Al 2 O 3 -poor mantle and a CaO-, Al 2 O 3 -rich crust, and later accretes significant amounts of water, a collision between it and an identical body can produce the necessary chemical conditions for condensation of CB chondrules. If the resulting impact plume is spatially heterogeneous in its proportions of crust and mantle components, the composition paths calculated for silicate condensates at the same P tot , Ni/H and Si/H ratios and water abundance that produce good matches to the unzoned metal grain compositions pass through the fields of BO and CC chondrules, especially if high-temperature condensates are fractionated in the case of the CCs. While equilibrium evaporation of an alloy containing solar proportions of siderophiles into a dense impact plume is an equally plausible hypothesis for explaining the compositions of the unzoned metal grains, equilibrium evaporation can explain CB chondrule compositions only if an implausibly large number of starting compositions is postulated. Kinetic models applied to co-condensing metal grains and silicate droplets in a region of the plume with very similar composition, but with high cooling rate and sharply declining P tot during condensation, produce very good matches to the zoning profiles of Ir, Ni, Co and Cr concentrations and Fe and Ni isotopic compositions observed in the zoned metal grains in CB chondrites but produce very large positive δ 56 Fe in the cogenetic silicate, which are not found in the chondrules.

The Antarctic carbonaceous chondrites DOM 08004 and DOM 08006 have been paired and classified as CO3.0s. There is some uncertainty as to whether they should be paired and whether they are best classified as CO chondrites, but they provide an opportunity for the study of refractory inclusions that have not been modified by parent body processes. In this work, refractory inclusions in thin sections of DOM 08004 and 08006 are studied and compared with inclusions in ALHA77307 (CO3.0) and Acfer 094 (C3.0, ungrouped). Results show that the DOM samples have refractory inclusion populations that are similar to each other but not typical of CO3 chondrites; main differences are that the DOM samples are slightly richer in inclusions in general and, more specifically, in the proportions of grossite-bearing inclusions. In DOM 08004 and DOM 08006, 12.4% and 6.6%, respectively, of the inclusions are grossite-bearing. This is higher than the proportion found in Acfer 094 (5.2%), whereas none were found in ALHA77307. Like those in Acfer 094, DOM inclusions are small (mostly

Ti valence measurements in MgAl_2O_4 spinel from calcium-aluminum-rich inclusions (CAIs) by X-ray absorption near-edge structure (XANES) spectroscopy show that many spinels have predominantly tetravalent Ti, regardless of host phases. The average spinel in Allende type B1 inclusion TS34 has 87% Ti^(+4). Most spinels in fluffy type A (FTA) inclusions also have high Ti valence. In contrast, the rims of some spinels in TS34 and spinel grain cores in two Vigarano type B inclusions have larger amounts of trivalent titanium. Spinels from TS34 have approximately equal amounts of divalent and trivalent vanadium. Based on experiments conducted on CAI-like compositions over a range of redox conditions, both clinopyroxene and spinel should be Ti^(+3)-rich if they equilibrated with CAI liquids under near-solar oxygen fugacities. In igneous inclusions, the seeming paradox of high-valence spinels coexisting with low-valence clinopyroxene can be explained either by transient oxidizing conditions accompanying low-pressure evaporation or by equilibration of spinel with relict Ti^(+4)-rich phases (e.g., perovskite) prior to or during melting. Ion probe analyses of large spinel grains in TS34 show that they are enriched in heavy Mg, with an average Δ^(25)Mg of 4.25 ± 0.028‰, consistent with formation of the spinel from an evaporating liquid. Δ^(25)Mg shows small, but significant, variation, both within individual spinels and between spinel and adjacent melilite hosts. The Δ^(25)Mg data are most simply explained by the low-pressure evaporation model, but this model has difficulty explaining the high Ti^(+4) concentrations in spinel.

We present high-precision measurements of the Mg isotopic compositions of a suite of types I and II chondrules separated from the Murchison and Murray CM2 carbonaceous chondrites. These chondrules are olivine- and pyroxene-rich and have low 27 Al/ 24 Mg ratios (0.012-0.316). The Mg isotopic compositions of Murray chondrules are on average lighter (d 26 Mg ranging from 0.95& to 0.15& relative to the DSM-3 standard) than those of Murchison (d 26 Mg ranging from 1.27& to +0.77&). Taken together, the CM2 chondrules exhibit a narrower range of Mg isotopic compositions than those from CV and CB chondrites studied previously. The least-altered CM2 chondrules are on average lighter (average d 26 Mg = 0.39 0.30&, 2SE) than the moderately to heavily altered CM2 chondrules (average d 26 Mg = 0.11 0.21&, 2SE). The compositions of CM2 chondrules are consistent with isotopic fractionation toward heavy Mg being associated with the formation of secondary silicate phases on the CM2 parent body, but were also probably affected by volatilization and recondensation processes involved in their original formation. The low-Al CM2 chondrules analyzed here do not exhibit any mass-independent variations in 26 Mg from the decay of 26 Al, with the exception of two chondrules that show only small variations just outside of the analytical error. In the case of the chondrule with the highest Al/Mg ratio (a type IAB chondrule from Murchison), the lack of resolvable 26 Mg excess suggests that it either formed >1 Ma after calcium-aluminum-rich inclusions, or that its Al-Mg isotope systematics were reset by secondary alteration processes on the CM2 chondrite parent body after the decay of 26 Al.

Research shows that 247Cm was present in meteorites at a level consistent with a single stellar environment of r-process nucleosynthesis., High-temperature condensates found in meteorites display uranium isotopic variations (235U/238U), which complicate dating the solar system’s formation and whose origin remains mysterious. It is possible that these variations are due to the decay of the short-lived radionuclide 247Cm (t1/2 = 15.6 My) into 235U, but they could also be due to uranium kinetic isotopic fractionation during condensation. We report uranium isotope measurements of meteoritic refractory inclusions that reveal excesses of 235U reaching ~+6% relative to average solar system composition, which can only be due to the decay of 247Cm. This allows us to constrain the 247Cm/235U ratio at solar system formation to (1.1 ± 0.3) × 10−4. This value provides new clues on the universality of the nucleosynthetic r-process of rapid neutron capture.

– For fayalite formation times of several thousand years, and systems enriched in water by a factor of ten relative to solar composition, 1 μm radius olivine grains could reach 2 mole% fayalite and 0.1 μm grains 5 mole% by nebular condensation, well short of the values appropriate for precursors of most chondrules and the values found in the matrices of unequilibrated ordinary chondrites. Even 10 μm olivine crystals could reach 30 mole% fayalite above 1100 K in solar gas if condensation of metallic nickel-iron were delayed sufficiently by supersaturation. Consideration of the surface tensions of several phases with equilibrium condensation temperatures above that of metallic iron shows that, even if they were supersaturated, they would still nucleate homogeneously above the equilibrium condensation temperature of metallic iron. This phenomenon would have provided nuclei for heterogeneous nucleation of metallic nickel-iron, thus preventing the latter from supersaturating significantly and preventing olivine from becoming fayalitic. Unless a way is found to make nebular regions far more oxidizing than in existing models, it is unlikely that chondrule precursors or the matrix olivine grains of unequilibrated ordinary chondrites obtained their fayalite contents by condensation processes. Perhaps stabilization of FeO occurred after condensation of water ice and accretion of icy planetesimals, during heating of the planetesimals and/or in hot, dense, water-rich vapor plumes generated by impacts on them. This would imply that FeO is a relatively young feature of nebular materials.

– Acfer 094 is an unshocked, nearly unaltered carbonaceous chondrite with an unusual suite of refractory inclusions. The refractory inclusions in a newly prepared thin section and a small aliquot of disaggregated material were studied to compare the population with previous work, and to report new or unusual inclusion types. A total of 289 Ca-, Al-rich inclusions in the thin section and 67 among the disaggregated material, having a total of 31 different mineral assemblages, were found. Inclusions are largely free of secondary alteration products, and are typically ≤200 μm across. The most common are gehlenitic melilite+spinel±perovskite, spinel+perovskite, and spinel with a thin, silicate rim, typically melilite±diopside. Such rims and (thicker) mantles are very common among Acfer 094 inclusions, and they exhibit a variety of zoning patterns with respect to akermanite and FeO contents. In the thin section, about 13% of the inclusions contain hibonite and approximately 5% are grossite-bearing; in the disaggregated material, the percentages are 14 and 9, respectively, comparable to previous work. Among the unusual inclusions are a fine-grained, porous, Ti-rich hibonite+spinel+perovskite+melilite inclusion with a compact, coarse, Ti-poor hibonite+spinel+melilite clast; two inclusions in which hibonite has reacted to form grossite; two inclusions with FeO-rich spinel; and a small object consisting of fassaite enclosing euhedral spinel, the first fragment of a Type B inclusion reported from Acfer 094. Inclusions similar to those found in CM or CV chondrites are rare; Acfer 094 contains a distinctive population of inclusions. The population, dominated by small, melilite-bearing inclusions, is most similar to that of CO chondrites. A distinguishing feature is that in Acfer 094, almost every phase in almost every refractory inclusion contains 0.5–1.5 wt% FeO. A lack of diffusion gradients and the pristinity of the matrix imply that the inclusions experienced prolonged exposure to FeO-bearing fluid prior to accretion into the Acfer 094 parent body. There are no known nebular conditions under which the refractory phases found in the present samples could acquire FeO enrichments to the observed levels. The most likely setting is therefore in an earlier, FeO-rich parent body. The inclusions were ejected from this parent body, mixed with typical CAIs, chondrules, amoeboid olivine aggregates, and amorphous material, and incorporated into the Acfer 094 parent body.

Micrometer-scale analyses of a calcium-, aluminum-rich inclusion (CAI) and the characteristic mineral bands mantling the CAI reveal that the outer parts of this primitive object have a large range of oxygen isotope compositions. The variations are systematic; the relative abundance of (16)O first decreases toward the CAI margin, approaching a planetary-like isotopic composition, then shifts to extremely (16)O-rich compositions through the surrounding rim. The variability implies that CAIs probably formed from several oxygen reservoirs. The observations support early and short-lived fluctuations of the environment in which CAIs formed, either because of transport of the CAIs themselves to distinct regions of the solar nebula or because of varying gas composition near the proto-Sun.

First, I want to thank Munir for the kind words, all those who took the time and effort to write letters nominating me for the Leonard Medal and, of course, the society’s Leonard Medal Committee for awarding me this great honor. I also want to express my appreciation to all the members of the Meteoritical Society, just for being such a fascinating group of smart scientists that provided such a vibrant and enjoyable research forum for so many years. It might seem strange to many of you that a kid who grew up on the city streets of Toronto, Canada, a country not particularly noted for its meteorite research, is standing before you today to receive the Leonard Medal. Let me try to convince you that it may not be so strange after all. I owe thanks to many institutions and people along the way whose advice and direction steered me toward this point in time. To my parents (Fig. 1), who instilled in me the importance of learning, despite their having less than a high school education themselves; to the Toronto public school system of the 1950s and 1960s, where success was rewarded and failure was an option; to the Toronto public library system (Fig. 2), where a young person’s extracurricular scientific interests could be satisfied; to the Royal Ontario Museum (Fig. 3), its Junior Field Naturalists, and the Walker Mineral Club, where a young mineral collector’s imagination could run wild; to Bay Street (Fig. 4), where a young boy lacking transportation to mineral collecting localities could go on a field trip by subway, collecting rare minerals by walking from office to office of many of Canada’s mining companies, headquartered in its skyscrapers; to Terry Seward (Fig. 5), a boyhood friend and fellow mineral collector, who steered me away from most Canadian universities whose geology programs were focused on the practical aspects of mineral exploration; and instead toward McMaster, my undergraduate university (Fig. 6), which was more oriented toward theoretical geochemistry; to my professors at McMaster, especially Jim Crocket, Bob McNutt, and Henry Schwarcz (Fig. 7), who all stressed the importance of physical chemistry, and directed me toward American graduate schools for pursuit of my interests in geochemistry; to all those faculty (Bob Gordon, Phil Orville, Brian Skinner), post-docs (Tom Brown, Jack Corliss, Lou Fernandez, Jiba Ganguly, Amitai Katz, Dinkar Kharkar), and graduate students (Don and Sharon Baschinski, Gary Brass, Julius Dasch, John Grover, Mark Kritz, John Morse) at the Kline Geology Lab at Yale University (Fig. 8), who combined to create what became a completely mind-expanding experience during my Ph.D. studies; and especially to my thesis advisers there (Fig. 9): Karl Turekian, a chemical oceanographer with extremely broad scientific interests, who was the first to introduce me to meteorites and was bold enough to supervise a Ph.D. thesis on chondrites; and Syd Clark, who taught me that there is usually a simple way to calculate a good first approximation to almost anything. Condensation calculations have come a long, long way from the days when I rode the New York, New Haven, and Hartford Railway between Yale and the NASA Goddard Institute for Space Studies in Manhattan, carrying multiple boxes of computer punch cards. I owe thanks to every Canadian university, each of which rejected my application for an assistant professorship in 1972, as my interest in meteorites probably would not have survived the scientific and funding priorities of the Canadian research scene; to Edward Anders, who politely listened to my expression of interest in a postdoctoral position in his lab at Chicago, and then gave me the biggest break of my career by suggesting that I apply instead for an assistant professorship at the same institution; to Joseph V. Smith (Fig. 10), who resurrected my appointment as assistant professor at Chicago just when all seemed lost; to the University of Chicago in general and the Department of the Geophysical Sciences (Fig. 11) and

Calcium Tschermak’s pyroxene (CaTs), CaAlAlSiO_6, is well known as an important component in pyroxene. It is a member of the Ca clinopyroxene group in which Al dominates in the M1 site. Pyroxenes with more than 80 mol% CaTs were observed previously in Ca-,Al-rich refractory inclusions (CAI) from five carbonaceous chondrites. This study re-investigated the near end-member CaTs in the Allende and Murray chondrites. Electron backscatter diffraction (EBSD) is used to establish that its crystal structure is monoclinic, C2/c; a = 9.609 A, b = 8.652 A, c = 5.274 A, β =106.06°, V = 421.35 A^3, and Z = 4. Its EBSD pattern is an excellent match to that of synthetic CaAlAlSiO_6 with the C2/c structure. MicroRaman is also carried out to confirm the crystal structure. The Allende CaTs, with 46.00 wt% Al_(2)O_3 and 97 mol% Al in the M1 site, has the formula Ca_(1.02)(Al_(0.97)Fe_(0.01)Mg_(0.01))0.99(Si_(1.00)Al_(1.00))_(Σ2.00)O_6. It occurs as micrometer-sized crystals along with melilite, hibonite, perovskite, spinel, corundum, Ti^(3+)-rich pyroxene, and grossular in a fluffy Type A CAI. It is probably a secondary phase resulting from the alteration of gehlenitic melilite. The CaTs in Murray, with a formula Ca_(0.98)(Al_(0.81)Mg_(0.16)Ti_(0.04)^(4+))_(Σ1.01)(Si_(1.11)Al_(0.89))_(Σ2.00)O_6, occurs with hibonite and Al-rich diopside in a glass-free refractory spherule. This sample formed by solidification of a once-molten droplet early in the history of the solar system.

Bulk chemical and O-, Mg- and Si-isotopic compositions were measured for each of 17 Types A and B refractory inclusions from CV3 chondrites. After bulk chemical compositions were corrected for non-representative sampling in the laboratory, the Mg- and Si-isotopic compositions of each inclusion were used to calculate its original chemical composition assuming that the heavy-isotope enrichments of these elements are due to Rayleigh fractionation that accompanied their evaporation from CMAS liquids. The resulting pre-evaporation chemical compositions are consistent with those predicted by equilibrium thermodynamic calculations for high-temperature nebular condensates, but only if different inclusions condensed from nebular regions that ranged in total pressure from 10−6 to 10−1 bar, regardless of whether they formed in a system of solar composition or in one enriched in dust of ordinary chondrite composition relative to gas by a factor of 10 compared to solar composition. This is similar to the range of total pressures predicted by dynamic models of the solar nebula for regions whose temperatures are in the range of silicate condensation temperatures. Alternatively, if departure from equilibrium condensation and/or non-representative sampling of condensates in the nebula occurred, the inferred range of total pressure could be smaller. Simple kinetic modeling of evaporation successfully reproduces observed chemical compositions of most inclusions from their inferred pre-evaporation compositions, suggesting that closed-system isotopic exchange processes did not have a significant effect on their isotopic compositions. Comparison of pre-evaporation compositions with observed ones indicates that 80% of the enrichment in refractory CaO + Al2O3 relative to more volatile MgO + SiO2 is due to initial condensation and 20% due to subsequent evaporation for both Types A and B inclusions.

We compare the observed composition ranges of olivine, pyroxene, and Fe-Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa096, with a pronounced frequency peak at Fa1. The composition range displayed by the low-calcium pyroxene is also very extensive, from Fs48 to Fs0, with a significant frequency peak centered at Fs5. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water-bearing minerals, the presence of Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major- and minorelement compositions of chondrite matrix and IDPs are required.

We report petrography, mineral chemistry, bulk chemistry, and bulk isotopic compositions of a suite of 40 spinel-rich inclusions from the Murchison (CM2) carbonaceous chondrite. Seven types of inclusions have been identified based on mineral assemblage: spinel-hibonite-perovskite; spinel-perovskite-pyroxene; spinel-perovskite-melilite; spinel-hibonite-perovskite-melilite; spinel-hibonite; spinel-pyroxene; and spinel-melilite-anorthite. Hibonite-bearing inclusions have Ti-poor spinel compared to the hibonite-free ones, and spinel-hibonite-perovskite inclusions have the highest average bulk TiO 2 contents (7.8 wt%). The bulk CaO/Al 2 O 3 ratios of the inclusions range from 0.005 to 0.21, well below the solar value of 0.79. Hibonite-, spinel-rich inclusions consist of phases that are not predicted by condensation calculations to coexist; in the equilibrium sequence, hibonite is followed by melilite, which is followed by spinel. Therefore, hibonite-melilite or melilite-spinel inclusions should be dominant instead. One explanation for the “missing melilite” is that it condensed as expected, but was lost due to evaporation of Mg and Ca during heating and melting of spherule precursors. If this theory were correct, melilite-poor spherules would have isotopically heavy Mg and Ca, assuming Rayleigh fractionation accompanied evaporation. Except for one inclusion with F Mg = 4.3 ± 2.6‰/amu and another with isotopically light Ca ( F Ca = −3.4 ± 2.0‰/amu), however, all the inclusions we analyzed have normal isotopic compositions within their 2σ uncertainties. Thus, we found no evidence for significant mass-dependent fractionation. Conditions necessary for non-Rayleigh evaporation are unlikely if not unrealistic, and our preferred explanation for the general lack of melilite among hibonite-, spinel-bearing inclusions is kinetic inhibition of melilite condensation relative to spinel. Because of similarities between the crystal structures of hibonite and spinel, it should be easier for spinel than for melilite to form from hibonite.

Most of the petrologic data available for Type B inclusions comes from Type B1s. Relatively little comes from the B2s, and there has not been a systematic comparison of the properties of their two most abundant minerals. In this work, we document the compositions and zoning patterns of melilite and fassaite in Type B2 inclusions, and compare and contrast them with the features of their counterparts in Type B1 inclusions. We find that melilite compositions in Type B2 inclusions are similar to those of Type B1s, with maximum Ak contents of ∼75 mol % and a positive correlation between Ak and Na 2 O contents. Asymmetrically zoned melilite is common in Type B2s as are melilite grains with reversely zoned regions, and the reversely zoned portions of crystals are thicker than in B1s. In B2s, like B1s, fassaite is zoned with decreasing Ti, Sc, and V oxide contents from cores to rims of grains. Approximately half of the Ti is trivalent, but unlike that in B1s, within fassaite grains in B2s the Ti 3+ /(Ti 3+ + Ti 4+ ) ratio does not decrease from core to rim, and sharp enrichments (“spikes”) in Ti 3+ and V are not observed. Sector-zoned fassaite is much more common in B2s than in B1s. The differences we observed can be accounted for by the differences in bulk compositions between B1s and B2s. Type B2 inclusions tend to have higher SiO 2 contents, hence higher An/Ge component ratios, than Type B1s. Phase equilibria show that, compared to B1s, in B2s less melilite should crystallize prior to the appearance of fassaite, so that in B2s a higher proportion of melilite cocrystallizes with fassaite, causing more of the crystals to be reversely zoned; more melilite crystallizes while adjacent to other crystals, leading to asymmetrical zoning; and with more liquid available, transport of components to growing fassaite occurs more readily than in B1s, facilitating crystal growth and giving rise to sector zoning. The lack of zoning with respect to Ti 3+ /Ti tot and the absence of Ti 3+ -, V-rich spikes suggest that Type B2 melts maintained equilibrium with the nebular gas throughout crystallization, while the interiors of B1s were probably isolated from the gas, perhaps by their melilite mantles. This makes the similarity of Na-Ak relationships in B1 and B2 melilite difficult to understand, but apparently enclosure by melilite mantles was not necessary for the retention of Na 2 O during crystallization of Type B refractory inclusions.

Melanoma risk factors include fair pigmentation, multiple nevi, low DNA repair capacity, and CDKN2A or CDK4 mutations. Variants of the melanocortin-1 receptor (MC1R) gene have been associated with fair pigmentation and melanoma risk, and a polymorphism of the Agouti Signaling Protein (ASIP) gene has been associated with dark pigmentation. We examined MC1R and ASIP genotypes in relation to phenotypic characteristics, sporadic and familial melanoma risk, and melanoma thickness as an indicator of disease progression in a Mediterranean population.We studied 267 melanoma patients and 382 control subjects from a case-control study and a family study in northeastern Italy. Host factors were assessed by physical examination, questionnaire, spectrophotometer, and minimal erythema dose measurement. MC1R was sequenced, ASIP was genotyped, and DNA repair capacity was measured by the host-cell reactivation assay. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression models. Effect modification of the association between MC1R and melanoma risk by phenotypic characteristics and DNA repair capacity was also assessed. All statistical tests were two-sided.Carrying MC1R variant alleles was associated with a two- to fourfold increase in risk of both sporadic and familial melanoma compared with carrying wild-type MC1R, particularly in individuals carrying multiple variant alleles (OR = 3.9; 95% CI = 3.3 to 4.6). This association was stronger in individuals with fewer additional risk factors (those with dark skin or few nevi). MC1R variant allele carriers were also three to four times more likely than were non-carriers to have thick melanomas. The ASIP polymorphism was not associated with pigmentation, nevi, or melanoma risk.MC1R was associated with melanoma risk and progression in a Mediterranean population, particularly in the absence of other strong risk factors, such as freckling or many nevi.

A large (7 mm in diameter) Allende type B inclusion has a typical bulk composition and a unique structure: a fassaite-rich mantle enclosing a melilite-rich core. The core and mantle have sharply contrasting textures. In the mantle, coarse (~1 mm across), subhedral fassaite crystals enclose radially oriented melilite laths about 500 m long that occur at the inclusion rim. The core consists of blocky melilite grains 20-50 μm across and poikilitically enclosed in anhedral fassaite grains that are optically continuous over ~1 mm. Another unique feature of this inclusion is that melilite laths also extend from the core into the mantle. Fassaite in both the core and mantle is very rich in fine-grained (1-10 μm) spinel. The rim laths are normally zoned (Ak 30-70) inward from the rim of the inclusion with reverse zoning over the last ~200 m to crystallize. A very wide range of melilite compositions is found in the core of the inclusion, where gehlenitic grains (Ak 5-12) occur. These grains are enclosed in strongly zoned (Ak 15-70) overgrowths. The gehlenitic cores and innermost parts of the overgrowths are Na2O-free, but the outer parts of the overgrowths are not. In the laths at the rim, Na2O decreases inward from the rim, then increases. Fassaite in the core has the same range of Ti contents as that in the mantle: 29 wt% TiO2 + Ti2O3. Two melting events are required to account for the features of this inclusion. In the first event, the precursor assemblage is heated to ~1400 °C and melts except for gehlenitic (Ak 5-12) melilite and some spinel. These grains become concentrated in the core. During cooling, Na2O-free melilite nucleates at the rim of the inclusion and on the relict grains in the core. After open system secondary alteration, the inclusion is heated again, but only to ~1260 °C. Melilite more gehlenitic than k40 does not melt. During cooling, Na2O-bearing melilite crystallizes as small, blocky grains and laths in the core and as overgrowths on relict grains in the core and at the rim. Eventually melilite co-crystallizes with fassaite, leading to the reverse zoning observed in the laths. The coexistence in this inclusion of Na-free and Na-bearing melilite, plus a positive correlation between Na2O and kermanite contents in melilite in an inclusion with a bulk Mg isotopic composition that is mass-fractionated in favor of the heavy isotopes, are both consistent with at least two melting events. Several other recently described coarse-grained inclusions also have features consistent with a sequence of early, high-temperature melting, secondary alteration, and remelting at a lower temperature, suggesting that remelting of refractory inclusions was a common occurrence in the solar nebula.

On the night of March 26, 2003, a large meteorite broke up and fell upon the south suburbs of Chicago. The name Park Forest, for the village that is at the center of the strewnfield, has been approved by the nomenclature committee of the Meteoritical Society. Satellite data indicate that the bolide traveled from the southwest toward the northeast. The strewnfield has a southeast-northwest trend; however, this is probably due to the effects of strong westerly winds at high altitudes. Its very low 56Co and very high 60Co activities indicate that Park Forest had a preatmospheric mass that was at least ~900 kg and could have been as large as ~7 x 10^3 kg, of which only ~30 kg have been recovered. The average compositions of olivine and low-Ca pyroxene, Fa24.7 ± 1.1 and Fs20.8 ± 0.7, respectively, and its bulk oxygen isotopic composition, δ18O = +4.68‰, δ17O = +3.44‰, show that Park Forest is an L chondrite. The ferromagnesian minerals are well equilibrated, chondrules are easily recognized, and maskelynite is mostly ≤50 μm across. Based on these observations, we classify Park Forest as type 5. The meteorite has been strongly shocked, and based on the presence of maskelynite, mosaicism and planar deformation features in olivine, undulatory extinction in pyroxene, and glassy veins, the shock stage is S5. The meteorite is a monomict breccia, consisting of light-colored, angular to rounded clasts in a very dark host. The light and dark lithologies have essentially identical mineral and oxygen isotopic compositions. Their striking difference in appearance is due to the presence of a fine, pervasive network of sulfide veins in the dark lithology, resulting in very short optical path lengths. The dark lithology probably formed from the light lithology in an impact that formed a sulfide-rich melt and injected it into cracks.

We recently reported an association between low DNA repair capacity, measured through the host-cell reactivation assay, and melanoma risk in subjects with dysplastic naevi or low tanning ability. We investigated the genetic basis for these findings by analysing the Asp312Asn and Lys751Gln polymorphisms of the XPD (ERCC2) DNA repair gene in the same subjects. Similar to our previous report, no significant association between XPD polymorphisms and melanoma risk was found in 176 melanoma cases and 177 controls (odds ratio (OR)=1.5, 95% confidence interval (CI)=0.9-2.5 for 312Asn; OR=1.3, 95% CI=0.8-2.1 for 751Gln, adjusted for age, gender, dysplastic naevi and pigmentation characteristics). However, XPD variants were associated with increased risk in older (>50 years) subjects (OR=3.4, 95% CI=1.6-7.3 for 312Asn; OR=2.3, 95% CI=1.1-4.9 for 751Gln). The 751Gln allele was associated with elevated melanoma risk among subjects without dysplastic naevi (OR=2.6, 95% CI=1.1-6.4). Subjects with low tanning ability and XPD variants exhibited a nonsignificant increase of melanoma risk (OR=2.3, 95% CI=0.7-7.0 for 312Asn; OR=3.0, 95% CI=1.0-8.8 for 751Gln). DNA repair capacity was slightly decreased in subjects carrying 751Gln alleles. XPD variants may modify melanoma risk in subjects with specific host characteristics, such as older age, lack of dysplastic naevi or low tanning ability.

Most studies of Tagish Lake have considered features that were either strongly affected by or formed during the extensive hydrous alteration experienced by this meteorite. This has led to some ambiguity as to whether Tagish Lake should be classified a CI, a CM, or something else. Unlike previous workers, we have focused upon the primary, anhydrous component of Tagish Lake, recovered through freeze-thaw disaggregation and density separation and located by thin section mapping. We found many features in common with CMs that are not observed in CIs. In addition to the presence of chondrules and refractory forsterite (which distinguish Tagish Lake from the CIs), we found hibonite-bearing refractory inclusions, spinel-rich inclusions, forsterite aggregates, Cr-, Al-rich spinel, and accretionary mantles on many clasts, which clearly establishes a strong link between Tagish Lake and the CM chondrites. The compositions of isolated olivine crystals in Tagish Lake are also like those found in CMs. We conclude that the anhydrous inclusion population of Tagish Lake was, originally, very much like that of the known CM chondrites and that the inclusions in Tagish Lake are heavily altered, more so than even those in Mighei, which are more heavily altered than those in Murchison.

We studied three newly diagnosed xeroderma pigmentosum complementation group G patients with markedly different clinical features. An Israeli-Palestinian girl (XP96TA) had severe abnormalities suggestive of the xeroderma pigmentosum/Cockayne syndrome complex including sun sensitivity, neurologic and developmental impairment, and death by age 6 y. A Caucasian girl (XP82DC) also had severe sun sensitivity with neurologic and developmental impairment and died at 5.8 y. In contrast, a mildly affected 14-y-old Caucasian female (XP65BE) had sun sensitivity but no neurologic abnormalities. XP96TA, XP82DC, and XP65BE fibroblasts showed marked reductions in post-ultraviolet cell survival and DNA repair but these were higher in XP65BE than in XP82DC. XP96TA fibroblasts had very low XPG mRNA expression levels whereas XP65BE fibroblasts had nearly normal levels. Host cell reactivation of an ultraviolet-treated reporter assigned all three fibroblast strains to the rare xeroderma pigmentosum complementation group G (only 10 other patients previously reported). XP96TA and XP82DC cells had mutations in both XPG alleles that are predicted to result in severely truncated proteins including stop codons and two base frameshifts. The mild XP65BE patient had an early stop codon mutation in the paternal allele. The XP65BE maternal allele had a single base missense mutation (G2817A, Ala874Thr) that showed residual ability to complement xeroderma pigmentosum complementation group G cells. These observations agree with earlier studies demonstrating that XPG mutations, which are predicted to lead to severely truncated proteins in both alleles, were associated with severe xeroderma pigmentosum/Cockayne syndrome neurologic symptoms. Retaining residual functional activity in one allele was associated with mild clinical features without neurologic abnormalities.

Through freeze-thaw disaggregation of the Murchison (CM) carbonaceous chondrite, we have recovered a ~90 x 75 μm refractory inclusion that consists of corundum and hibonite with minor perovskite. Corundum occurs as small (~10 μm), rounded grains enclosed in hibonite laths (~10 μm wide and 30-40 μm long) throughout the inclusion. Perovskite predominantly occurs near the edge of the inclusion. The crystallization sequence inferred petrographically - corundum followed by hibonite followed by perovskite - is that predicted for the first phases to form by equilibrium condensation from a solar gas for Ptot ≤ 5 x 10^(-3) atm. In addition, the texture of the inclusion, with angular voids between subhedral hibonite laths and plates, is also consistent with formation of the inclusion by condensation. Hibonite has heavy rare earth element (REE) abundances of ~40 x CI chondrites, light REE abundances ~20 x CI chondrites, and negative Eu anomalies. The chondrite-normalized abundance patterns, especially one for a hibonite-perovskite spot, are quite similar to the patterns of calculated solid/gas partition coefficients for hibonite and perovskite at 10^(-3) atm and are not consistent with formation of the inclusion by closed-system fractional crystallization. In contrast with the features that are consistent with a condensation origin, there are problems with any model for the formation of this inclusion that includes a molten stage, relic grains, or volatilization. If thermodynamic models of equilibrium condensation are correct, then this inclusion formed at pressures

We found a common biallelic polymorphism (PAT) in the xeroderma pigmentosum complementation group C (XPC) DNA repair gene consisting of an insertion of 83 bases of A and T [poly(AT)] and a 5 base deletion within intron 9. We developed a PCR assay to resolve the XPC PAT+ and PAT- alleles and found that the PAT+ allele frequency was 0.44 in 156 cancer-free donors from the Johns Hopkins School of Public Health, 0.41 in 263 cancer-free donors from the Baltimore Longitudinal Study of Aging and 0.36 in samples from 216 unselected donors from NIH. We also found a single nucleotide polymorphism in exon 15 of the XPC gene (A2920C, Lys939-->Gln) that creates a new enzyme restriction site. This XPC exon 15 single nucleotide polymorphism occurred at a frequency of 0.38 in 98 NIH donors and is in linkage disequilibrium with the PAT locus. We developed an allele-specific complementation assay utilizing post-UV host cell reactivation to assess DNA repair capacity of polymorphic alleles. We found similar DNA repair with XPC 2920A and XPC 2920C. These common polymorphisms in the XPC DNA repair gene may be useful for molecular epidemiological studies of cancer susceptibility.

— In addition to the Mg-, Al-, 16O-rich spinels that are known to occur in refractory inclusions, the Murchison meteorite contains Cr-rich, 16O-poor spinels, most of whose sources are unknown because they are rarely found in situ. Here we report the in situ occurrence in Allende of Cr-rich spinels, found in 13 chondrules and 4 “olivine-rich objects”. The Allende spinels exhibit major and minor element contents, isotopic compositions, and zoning of Cr2O3 contents like those of the Cr-spinels from Murchison. Some chondrules contain patchy-zoned spinel (Simon et al., 1994), which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains. Unlike the olivine-rich objects, phases in all three chondrules that were analyzed by ion microprobe have uniform, near-normal O-isotopic compositions. One olivine-rich object, ALSP1, has a huge (1 mm) fragment of chevron-zoned spinel. This spinel has near-normal O-isotopic compositions that are quite distinct from those of adjacent forsteritic olivine, which are relatively 16O-rich and plot on the calcium-aluminum-inclusion (CAI) line, like some isolated forsterite grains found in Allende. The spinel and olivine in this object are therefore not genetically related to each other. Another olivine-rich object, ALSP11A, contains a rectangular, 150 ×s 100 μm, homogeneous spinel grain with 50 wt% Cr2O3 and 23 wt% FeO in a vuggy aggregate of finer-grained (5–90 μm), FeO-rich (Fo47–55) olivine. The magnesian core of one olivine grain has a somewhat 16O-rich isotopic composition like that of the large spinel, whereas the FeO-rich olivine is relatively 16O-poor. The composition of the spinel in ALSP11A plots on the CAI line, the first Cr-rich spinel found to do so. Chevron-zoned spinel has not been observed in chondrules, and it is unlikely that either ALSP1 or ALSP11A were ever molten. Calculations show that a spinel with the composition of that in ALSP1 can condense at 1780 K at a Ptot of 10−3 atm and a dust/gas ratio of 100 relative to solar. The Cr-rich spinel in ALSP11A could condense at ∼1420 K, but this would require a dust/gas enrichment of 1000 relative to solar. The data presented here confirm that, as in Murchison, the coarse Cr-rich spinels in Allende are relatively 16O-depleted and are isotopically distinct from the 16O-enriched MgAl2O4 from CAIs. Sample ALSP11A may represent a third population, one that is Cr-rich and plots on the CAI line. That the O-isotopic composition of ALSP1 is like those of Cr-rich spinels from chondrules indicates that O-isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules.

A combination of hydrodynamic and cross-linking studies were used to investigate self-assembly of the Escherichia coli DNA repair protein UvrB. Though the procession of steps leading to incision of DNA at sites flanking damage requires that UvrB engage in an ordered series of complexes, successively with UvrA, DNA, and UvrC, the potential for self-association had not yet been reported. Gel permeation chromatography, nondenaturing polyacrylamide gel electrophoresis, and chemical cross-linking results combine to show that UvrB stably assembles as a dimer in solution at concentrations in the low micromolar range. Smaller populations of higher order oligomeric species are also observed. Unlike the dimerization of UvrA, an initial step promoted by ATP binding, the monomer-dimer equilibrium for UvrB is unaffected by the presence of ATP. The insensitivity of cross-linking efficiency to a 10-fold variation in salt concentration further suggests that UvrB self-assembly is driven largely by hydrophobic interactions. Self-assembly is significantly weakened by proteolytic removal of the carboxyl terminus of the protein (generating UvrB*), a domain also known to be required for the interaction with UvrC leading to the initial incision of damaged DNA. This suggests that the C terminus may be a multifunctional binding domain, with specificity regulated by protein conformation.

The small DNA fragment thymidine dinucleotide (pTpT) stimulates photoprotective responses in mammalian cells and intact skin. These responses include increased melanogenesis (tanning) and enhanced repair of DNA damage induced by ultraviolet (UV) light. Here we show that pTpT treatment of human keratinocytes enhances their repair of DNA damaged by the chemical carcinogen benzo(a)pyrene (BP), as determined by increased expression of a transfected BP-damaged reporter plasmid containing the chloramphenicol acetyltransferase (CAT) gene. The pTpT-enhanced repair of this BP-damaged plasmid is accomplished at least in part through activation of the p53 tumor suppressor protein and transcription factor, because p53-null H1299 cells showed enhanced repair only if previously transfected with a p53-expression vector. To elucidate the mechanism of this enhanced DNA repair, we examined the expression of p21 and proliferating cell nuclear antigen (PCNA), proteins known to be regulated by p53, as well as the XPA protein, which is mutated in the inherited repair-deficient disorder xeroderma pigmentosum (XP) group A and is necessary for the recognition of UV-induced DNA photoproducts. The p53, PCNA and XPA proteins were all up-regulated within 48 h after the addition of pTpT. Taken together, these data demonstrate that pTpT-enhanced repair of DNA damaged by either UV irradiation or chemical mutagens can be achieved in human cells by exposure to small DNA fragments at least in part through the activation of p53 and increased expression of p53-regulated genes.

— We have studied both of the known glass-free, hibonite-pyroxene spherules: MYSM3, from Murray (CM2), and Y17–6, from Yamato 791717 (CO3). They consist of hibonite plates (∼2 wt% TiOtot2) enclosed in Al-rich pyroxene that has such high amounts of CaTs (CaAl2SiO6) component, up to ∼80 mol%, that it must have crystallized metastably. Within the pyroxene, abundances of MgO and SiO2 are strongly correlated with each other and are anticorrelated with those of Al2O3, reflecting an anticorrelation between the diopside and CaTs components of the pyroxene. In contrast with previous results for Type B fassaite, however, we do not observe an anticorrelation between MgO and TiOtot2, possibly reflecting different relative distribution coefficients for Ti3+ and Ti4+ in the aluminous pyroxene of the spherules from those found for fassaite in Type B inclusions. Previously described hibonite-silicate spherules have 26Mg deficits but the present samples do not. Furthermore, the pyroxene in Y17-6 has excess 26Mg, while the hibonite it encloses does not, indicating that the two phases either had different initial 26Al/27Al ratios or different initial 26Mg/24Mg ratios. The Ti isotopic compositions of the present samples are highly unusual: δ50Ti = 103.4 ± 5.2%o in MYSM3 and -61.4 ± 4.1%0 in Y17-6, which are among the largest 50Ti anomalies reported for any refractory inclusion. The textures suggest that hibonite crystallized first; but based on the calculated bulk compositions of both spherules, it is not the liquidus phase in either sample, which suggests that the hibonite in both samples is relict. The presence of ragged hibonite grains in MYSM3 and rounded hibonite grains in Y17-6 and a lack of isotopic equilibrium between pyroxene and hibonite support this conclusion. The spherules crystallized from liquid droplets that probably formed as a result of the melting of solid precursor grains that included hibonite. The heating events were too short and/or not hot enough to melt all the hibonite. The droplets cooled quickly enough that CaTs-rich pyroxene crystallized instead of anorthite. Based on the observed differences in isotopic composition, it is unlikely that the precursors of the present samples formed in the same reservoir as each other or as the previously described hibonite-silicate spherules, providing further evidence of the isotopic heterogeneity of the early solar nebula.

— We report the results of a study of TS2, an unusual compact Type A inclusion from Allende. A distinctive, major feature of this inclusion is that many of its melilite crystals have no dominant core-rim zoning but instead consist of 50–200 μm patches of Mg-rich melilite (Ak32–62, median Ak51) set in or partially enclosed by, and optically continuous with, relatively Al-rich melilite (Ak25–53, median Ak38). The Al-rich regions have jagged, dendritic shapes but occur within crystals having straight grain boundaries. Another unusual feature of this inclusion is the size and spatial distribution of spinel. In many places, especially in the interior of the inclusion, the aluminous melilite encloses numerous, fine (0.5–5 μm) inclusions of spinel and minor perovskite and fassaite. The latter phases also occur as isolated grains throughout the inclusion. Coarse-grained spinel, ∼50–150 μm across, occurs in clumps and chains enclosed in relatively Mg-rich melilite, whereas none of the fine spinel grains are clumped together. The sample also contains a spinel-free palisade body, 1.7 × 0.85 mm, that consists almost entirely of Ak-rich (45–65 mol%) melilite. Within the palisade body are two grains of perovskite with extremely Nb-rich (∼4–8 wt% Nb2O5) cores and rims of typical composition. All phases in this inclusion have chondrite-normalized REE patterns that are consistent with crystal/melt partitioning superimposed upon a bulk modified Group II pattern. We suggest that TS2 had an anomalous cooling history and favor the following model for the formation of TS2. Precursors having a bulk modified Group II pattern melted. Rapid growth of large, dendritic, nonstoichiometric melilite crystals occurred. The melilite trapped pockets of melt and incorporated excess spinel components and TiO2. Bubbles formed in the residual melt. As crystallization slowed, coarse spinel grew. Some spinel grains collected against bubbles, forming spherical shells, and others formed clumps and chains. Relatively Ak-rich melilite crystallized from the residual melt between dendritic melilite crystals and from melt trapped in pockets and between arms of dendrites, and incorporated the clumps and chains of coarse spinel. Bubbles broke and filled with late-stage melt, their shapes preserved by their spinel shells. Slow cooling, or perhaps an episode of reheating, allowed the early melilite to become stoichiometric by exsolving fine grains of spinel, perovskite and fassaite, and allowed the melilite to form smooth grain boundaries. Dendritic crystals are indicative of rapid growth and the melilite crystals in TS2 appear to be dendritic. Coarse, dendritic melilite crystals have been grown from Type B inclusion melts cooled at ∼50–100 °C/h. If those results are applicable to Type A inclusions, we can make the first estimate of the cooling rate of a Type A inclusion, and it is outside the range (2–50 °C/h) generally inferred for Type B inclusions. The rapid cooling inferred here may be part of an anomalous thermal history for TS2, or it may be representative of part of a normal thermal history common to Types A and B that involved rapid cooling early (at high temperatures) as inferred for TS2, and slower cooling later (at lower temperatures), as inferred for Type B inclusions. We prefer the former explanation; otherwise, the unusual features of TS2 that are reported here would be common in Type A inclusions (which they are not).

The entire process of nucleotide excision repair (NER) in Escherichia coli has been reconstituted in vitro from purified proteins and defined DNA substrates. However, how this system is organized in vivo in unclear. We report here the isolation and characterization of macromolecular assemblies containing NER and transcription proteins from E. coli. This ensemble consists of at least 17 proteins. They are recruited, as a consequence of DNA damage induced by UV irradiation, to the inner membrane. The UV-induced 6-4 photoproducts are also relocated to the inner membrane following UV-irradiation of the cells. This recruitment process is dependent on the uvrA, uvrC and recA gene products. These results suggest that at least part of the repair process may associate with the inner membrane and also provide insights into understanding the cellular organization of repair processes.

— Through freeze-thaw disaggregation of the Murchison meteorite, we have recovered, in addition to many spinel-hibonite spherules, several hibonite-rich inclusion fragments in which the hibonite has wider ranges in TiO2 contents (e.g., 0.07–8.6 wt% in one inclusion and 2–10 wt% in another) than previously observed within single inclusions. In these inclusions, there are sharp contacts between texturally early, Ti-poor hibonite and relatively late, Ti-rich hibonite, and the two types occur in complex intergrowth textures that are not consistent with crystallization from a melt in a single-stage cooling event. One inclusion has, in addition to relatively TiO2-rich hibonite, some that is virtually TiO2-free but contains ∼1 wt% MgO and ∼1.5 wt% SiO2. Instead of the common substitution of Mg + Ti for 2Al, Mg coupled with Si in this case, probably reflecting crystallization from an unusual, Ti-free silicate liquid. Ion microprobe analyses of Ti-rich and Ti-poor hibonite from this inclusion yield quite similar trace-element patterns and Mg-isotopic compositions. The results are most consistent with formation of Ti-rich hibonite from Ti-poor hibonite by addition of Mg and Ti to the latter by exchange with a hot, Ti-rich liquid. That this occurred without a resolvable change in the Mg-isotopic composition requires that the Ti-rich, second generation of hibonite formed

— It has been suggested that palisade bodies—shells of spinel found within some calcium, aluminum-rich inclusions (CAIs) and the phases the shells enclose—are intact mini-CAIs that predate and were captured by their current hosts while the latter were still molten. We present new data and observations that indicate that most palisade bodies formed instead in situ while their host inclusions were crystallizing. The evidence includes observations of spinel-lined cavities and glass-filled, circular structures outlined by spinel in experimental run products crystallized from melts; a partially formed palisade body in an inclusion; a fassaite crystal that is optically continuous across a palisade wall; and similarity of unusual mineral compositions in some palisade bodies and their hosts. Our observations can be used to refute arguments for exotic origin and are most consistent with a model for in situ formation involving: (1) formation of vesicles in a largely molten inclusion; (2) nucleation of spinel upon and/or adherence to vapor-melt interfaces, forming spinel shells around vesicles; (3)leakage of vesicles and filling with melt while spinel shells remain largely intact; and (4) crystallization of melt inside shells. This model is similar to one proposed for formation of segregation vesicles, which are partially- to completely-filled vesicles found in some terrestrial basalts. In addition, we interpret framboids (i.e., dense clusters of spinel with little material between grains, found in most inclusions that contain palisade bodies) as polar or near-polar sections through palisade bodies and therefore do not make a genetic distinction between the two features.

Karl Karekin Turekian (1927–2013) was a man of remarkable scientific breadth, with innumerable important contributions to marine geochemistry, atmospheric chemistry, cosmochemistry, and global geochemical cycles. He was mentor to a long list of students, postdoctorate scholars, and faculty (at Yale and elsewhere), a leader in geochemistry, a prolific author and editor, and had a profound influence in shaping his department at Yale University. Karl was a true scholar and interested in everything, scientific and nonscientific. As his Yale colleague George Veronis reflected, “Karl plunged into any topic, very often far removed from his own specialty, and had heated discussions about all kinds of issues. His discussions were heated because that’s how he got himself worked up to carry on the way he did. Very often he would say something like, ‘I don’t know anything about so and so,’ when a topic was raised, and quite often he didn’t. He wanted to learn, and his own ignorance would not deter him from carrying on.” Karl’s autobiography (1) and a recent interview (2) tell his story far better than we can and make clear his vast contributions to science, especially his role in the development and advancement of the field of geochemistry. What is especially notable about Karl is his impact on people, the unanimity of the love for Karl by all who knew him well, and his unique character. We’d like to recount a little of what it was like to be on the receiving end of his warmth and wisdom.

The Escherichia coli Uvr(A)BC endonuclease (Uvr(A)BC) initiates nucleotide excision repair of a large variety of DNA damages. The damage recognition and incision steps by the Uvr(A)BC is a complex process utilizing an ATP-dependent DNA helix-tracking activity associated with the UvrA2B1 complex. The latter activity leads to the generation of highly positively supercoiled DNA in the presence of E. coli topoisomerase I in vitro. Such highly positively supercoiled DNA, containing ultraviolet irradiation-induced photoproducts (uvDNA), is resistant to the incision by Uvr(A)BC, whereas the negatively supercoiled and relaxed forms of the uvDNA are effectively incised. The E. coli gyrase can contribute to the above reaction by abolishing the accumulation of highly positively supercoiled uvDNA thereby restoring Uvr(A)BC-catalyzed incision. Eukaryotic (calf thymus) topoisomerase I is able to substitute for gyrase in restoring this Uvr(A)BC-mediated incision reaction. The inability of Uvr(A)BC to incise highly positively supercoiled uvDNA results from the failure of the formation of UvrAB-dependent obligatory intermediates associated with the DNA conformational change. In contrast to Uvr(A)BC, the Micrococcus luteus UV endonuclease efficiently incises uvDNA regardless of its topological state. The in vitro topodynamic system proposed in this study may provide a simple model for studying a topological aspect of nucleotide excision repair and its interaction with other DNA topology-related processes in E. coli.

Based on the binding of the UvrAB complex to a promoter region in transcription open complexes (Ahn, B., and Grossman, L. (1996) J. Biol. Chem. 271, 21453-21461) and the requirement of a single-stranded region for UvrAB helicase activity, we examined the binding of UvrAB proteins to synthetic bubble or loop regions in duplex DNA and the role of these regions in translocation of the UvrAB complex as well as incision of DNA damage. We found that the UvrAB complex was able to bind to bubble and loop regions with an affinity similar to that for damaged DNA in the absence of RNAP. The preferential recognition and incision of damaged sites by the UvrAB complex was observed downstream of the bubble or loop region in the strand complementary to the strand along which the UvrAB complex translocates. These results imply that the bubble region generated in duplex DNA by RNAP serves as a preferred entry site for the translocation of the UvrAB complex, and that preferential binding and unidirectional translocation of the UvrAB complex predetermine where incision is to occur.

— Through freeze-thaw disaggregation of the Murchison meteorite, we have recovered a refractory inclusion, HIB-11, that is unique in terms of its texture, mineral compositions, and bulk composition. It consists of anhedral, Y-rich (1.6 wt% Y2O3) perovskite and lathlike spinel grains enclosed in a matrix of fine-grained, Sc-rich (10.5 wt% SC2O3 avg.), Ti-rich (12.6 wt% TiO2 avg., reporting all Ti as TiO2) clinopyroxene. The chondrite-normalized rare earth element (REE) pattern is complex, with light REE (LREE) at ∼10× C1, abundances increasing from Gd through Ho (the latter at ∼104× C1), decreasing through Yb at 200× C1, and Lu at ∼400× C1. The pattern reflects several stages of high-temperature volatility fractionation. Removal of Lu and Er from the source gas in the first condensation event was followed by partial to complete removal of the somewhat less refractory heavy REE, Gd through Ho, in the HIB-11 precursors by condensation from the fractionated residual gas in a second event. Both of these events probably reflect condensation of REE into ZrO2 or a mixed Zr-, Sc-, Ti-, Y-oxide at temperatures too high for hibonite stability. A second, lower-temperature component, which was subsequently added, had fractionated (Nd-poor, Ce-rich) LREE abundances that resulted from condensation from a gas that had undergone prior removal of the more refractory LREE, resulting in enrichment in Ce and the most volatile REE, Eu and Yb. The aggregate was then melted and quickly cooled, forming a fine-grained spherule. This is the first reported inclusion in which the two most refractory REE, Lu and Er, are strongly fractionated from the other REE. An absence of mass fractionation among the Ti isotopes indicates that HIB-11 is not an evaporative residue, implying that volatility fractionation of trace elements took place during condensation. The fact that the two most refractory heavy REE could be separated from the other, only slightly less refractory heavy REE suggests that a wide variety of REE patterns is possible, and that ultrarefractory inclusions with other unusual REE patterns, important recorders of nebular condensation, may yet be discovered.

We describe a previously unreported meteorite found in Axtell, Texas, in 1943. Based on the mineralogical composition and texture of its matrix and the sizes and abundance of chondrules, we classify it as a CV3 carbonaceous chondrite. The dominant opaque phase in the chondrules is magnetite, and that in refractory inclusions is Ni-rich metal (awaruite). Axtell, therefore, belongs to the oxidized subgroup of CV3 chondrites, although unlike Allende it escaped strong sulfidation. The meteorite bears a strong textural resemblance to Allende, and its chondrule population and matrix appear to be quite similar to those of Allende, but its refractory inclusions, thermoluminescence properties, and cosmogenic Co-60 abundances are not. Our data are consistent with a terrestrial age for Axtell of approximately 100 years and a metamorphic grade slightly lower than that of Allende.

The Escherichia coli Uvr(A)BC endonuclease acts in a progression of several distinct steps accompanied by changes in the conformation of macromolecular constituents, the overall architecture of the complex, and its stoichiometry. In order to probe these structural changes, we generated monoclonal antibodies (mAbs) to Uvr proteins. The anti-UvrA mAb, A2D1, recognizing the N-terminal zinc-finger region of UvrA, and the anti-UvrB mAb, B2E2, having an epitope within the 43 C-terminal amino acids of UvrB, were purified and further characterized. It was found that A2D1 mAb interacts in solution both with UvrA-UvrB and UvrA-DNA complexes in the presence of the requisite ATP. This implies that the N-terminal zinc-finger of UvrA doesn't play a direct role in its interactions with UvrB and DNA. On the other hand, A2D1 does inhibit formation of the UvrB-damaged DNA preincision complex, apparently by preventing UvrB delivery by UvrA. The interaction of B2E2 with UvrA-UvrB and nucleoprotein complexes, including UvrB, suggests that the highly hydrophobic C-terminal domain of UvrB (i) doesn't participate in its interaction with UvrA, (ii) is accessible to this mAb in an intermediate UvrA-UvrB DNA helix-tracking complex, and (iii) seems to be directly involved in the formation of the preincision complex. These conclusions are supported by the finding that the neutralizing effect of A2D1 and B2E2 on the Uvr(A)BC endonuclease is significantly decreased if the preincision complex is preformed prior to mAbs addition.

The cysteine 763 residue in the C-terminal zinc-finger region of Escherichia coli UvrA protein was subjected to random mutagenesis, and the results suggested that the UvrA mutants with a small amino acid (Ser, Ala, or Gly) substituting for the cysteine 763 were almost as active as the wild-type in supporting nucleotide excision repair, but its replacement with a large, bulky amino acid (Tyr, Trp, or Phe) rendered the mutants inactive. The C763F mutant UvrA protein was purified for further characterization, and it was found this mutant UvrA protein lost its DNA binding (single-stranded or double-stranded DNA) activity and those other activities dependent on DNA binding, such as formation of damage-specific UvrA2B complexes and the supercoiling reaction. However, this mutant protein retained vigorous ATPase activity and was capable of negatively complementing the wild-type UvrA in JM109 strain. The purified C763F mutant UvrA protein contains a single zinc ion/molecule, half that of the wild-type. It appears that the C763F mutation destabilizes the zinc-anchored structure in the C-terminal zinc finger region, and as a result, the C763F mutant UvrA protein lost its ability to bind DNA.

Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the IIE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new IIE iron. Whole rock Watson silicate shows an enrichment in K and P (each approximately 2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa20), opx (Fs17Wo3), capx (Fs9Wo14)(with very fine exsolution lamellae), antiperthite feldspar (An1-3Or5) with less than 1 micron exsolution lamellae (An1-3Or greater than 40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of approximately 300X and 100-150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or13, and in the presence of antiperthite.

Most spinel grains in Murchison acid residues are Mg-, Al-rich, 16O-rich (δ18O = −50%.), small (10–30 μm) and probably from refractory inclusions. They are quite unlike spinels we have recovered from Murchison by freeze-thaw disaggregation, density separation, and handpicking. As reported here, the latter spinels contain up to 37 wt% Cr2O3 and up to 17 wt% FeO, are not 16O-enriched (δ18O = 1.9 ± 2.4%.), are coarse (60–325 μm), and are not from refractory inclusions. From backscattered electron images of fifty-seven such grains, we recognize five zoning types defined by variations in Cr2O3 contents: patchy (56%); homogeneous (21%); chevron (10.5%); gradational (9%); and core-rim (3.5%). Many grains have silicate inclusions, the most common being small, anhedral grains of diopside with 12–24 wt% Al2O3 and up to 3.7 wt% TiO2. Eleven spinel samples occur with forsteritic (Fo95–99) olivine; in most cases, the spinel partially encloses the olivine. Cr-bearing spinel was found in situ in two Al-rich chondrules (one with homogeneous spinel, the other with homogeneous, gradational and core-rim spinel, and both with forsterite and aluminous diopside); in two irregularly shaped, olivine-bearing inclusions (one with homogeneous spinel, the other patchy); and attached to an isolated olivine grain (patchy). Observation of homogeneous, gradational, and core-rim type spinels in chondrules and basalts shows that grains with these zoning patterns can crystallize from liquids, although, in Murchison, chondrules with the appropriate compositions and sufficiently coarse textures to yield the separated spinels are exceedingly rare. Chevronzoned grains also could have formed in chondrules; alternatively, they may have acquired their oscillatory zoning patterns by cycling through different P-T-ƒ O 2 regimes in the solar nebula during their formation. The patchy spinel grains were probably never molten and they most likely formed by sintering of aggregates of smaller spinel grains which were enriched in Cr and Fe to varying degrees. In spite of their various crystallization and thermal histories, the spinels all have normal oxygen and chromium isotopic compositions, consistent with formation from a single, well-mixed nebular reservoir. Based on the known slow rates of diffusion of oxygen in MgO, Al2O3, and MgAl2O4, it is unlikely that the spinels of this study formed from an isotopically anomalous reservoir and later re-equilibrated with a normal one; it is more likely that they have retained their original isotopic compositions. We see no evidence for anomalous Cr, which had been reported by others.