Context. The properties of the smallest subunits of cometary dust contain information on their origin and clues to the formation of planetesimals and planets. Compared to interplanetary dust ...particles or particles collected during the Stardust mission, dust collected in the coma of comet 67P/Churyumov-Gerasimenko (67P) during the Rosetta mission provides a resource of minimally altered material with known origin whose structural properties can be used to further the investigation of the early solar system. Aims. The cometary dust particle morphologies found at comet 67P on the micrometer scale are classified, and their structural analysis is extended to the nanometer scale. Methods. We present a novel method for achieving the highest spatial resolution of imaging obtained with the MIDAS Atomic Force Microscope on board Rosetta. 3D topographic images with resolutions down to 8 nm were analyzed to determine the subunit sizes of particles on the nanometer scale. Results. Three morphological classes can be determined: (i) fragile agglomerate particles of sizes larger than about 10 μm comprised of micrometer-sized subunits that may themselves be aggregates and show a moderate packing density on the surface of the particles. (ii) A fragile agglomerate with a size of about a few tens of micrometers comprised of micrometer-sized subunits that are suggested to be aggregates themselves and are arranged in a structure with a fractal dimension lower than two. (iii) Small micrometer-sized particles comprised of subunits in the size range of hundreds of nanometers that show surface features that are again suggested to represent subunits. Their differential size distributions follow a log-normal distribution with means of about 100 nm and standard deviations between 20 and 35 nm. Conclusions. The properties of the dust particles found by MIDAS represent an extension of the dust results of Rosetta to the micro- and nanometer scale. All micrometer-sized particles are hierarchical dust agglomerates of smaller subunits. The arrangement, appearance, and size distribution of the smallest determined surface features are reminiscent of those found in chondritic porous interplanetary dust particles. They represent the smallest directly detected subunits of comet 67P.
The 2.02 billion year old Vredefort impact structure in South Africa offers a unique opportunity to study large‐scale impact processes on Earth. Vredefort's large size (∼250 km in diameter) and ...eroded topography provides the opportunity to study the effects of shock physics at depth and post‐formation hydrothermal alteration. In this work, we simulate the formation of the Vredefort structure building upon recent shock physics (iSALE) simulations. We expand those simulations to cover a wider range of input conditions, and compute impact‐driven porosity and permeability. The latter quantities are used to perform fluid mobility simulations (HYDROTHERM). We find that the Vredefort event produced significant impact‐generated porosity (up to 30%) in an annulus from about 50 to 100 km from the center and up to several kilometers in depth. The corresponding estimated permeability (up to 10−12 m2) would have allowed for large scale subsurface fluid flows. Our hydrothermal calculations show that the Vredefort impact event could have generated a complex crustal fluid pattern within the crater rim that lasted for hundreds of thousand years, with localized flow concentration regions, opening a new interpretation for the mobilization and location of the ore deposits in the Witwatersrand basin. The combined approach utilizing impact and hydrothermal simulations constitute a powerful tool to understand geochemical processes at Vredefort, as well as to assess the ability of large impacts to drive crustal chemistry with far‐reaching consequences for the prebiotic evolution of the early Earth.
Key Points
Vredefort impact event generated widespread crustal porosity and permeability
Post‐impact hydrothermal alteration lasted for 100s of thousands of years
Large‐scale impacts are an important source of crustal fluid mobility in the early Earth
Remnants of paleoflora were discovered in impact melt rocks from the El'gygytgyn crater, Chukotka, Russia. El'gygytgyn is a 3.58 Ma, 18 km diameter impact structure in Chukotka, northeastern Russia. ...A circular crater basin is surrounded by an uplifted rim. The crater floor is occupied by the El'gygytgyn Lake, 12 km in diameter, surrounded by lacustrine terraces up to 80 m in height. Impactites found at the El'gygytgyn crater include impact melt rocks, glass bombs, and shock metamorphosed volcanic rocks. Most impact melt rocks occur only in redeposited state in the terrace lake deposits. Floral remnants were discovered in impact melt rocks from various locations in the terrace deposits. The floral remnants include fragments of leaves, cell tissue, and undetermined organic matter that occur in vesicles within glassy melt rocks and impact melt breccias. After the discovery of floral remnants in impact melt breccias from upper Miocene strata in Argentina, and the description of floral imprints in the Dakhleh Glass of proposed impact origin in Egypt, the detection of paleoflora remnants in impact melt rocks of the El'gygytgyn structure is the first such occurrence in a confirmed impact crater on Earth.
Metallic resources in smartphones Bookhagen, B.; Bastian, D.; Buchholz, P. ...
Resources policy,
October 2020, 2020-10-00, 20201001, Letnik:
68
Journal Article
Recenzirano
53 metallic elements from smartphones were investigated with regard to metal prices, metal production, and content in comparison to mined ores. The metal content of the 7.42 billion smartphone ...devices sold from 2012 to 2017 could theoretically maintain the global supply for 91 days for Ga, 73 days for Ta, 23 days for Pd, 14 days for Au, and 6 days for REE. The pure metal value of a single smartphone device for the investigated metals currently sums to 1.13 US $; it averaged at 1.05 US $ from 2012 to 2017 with the highest value of 1.32 US $ in 2012. The Au content is low (16.83 mg per device), yet constitutes the highest value with a current share of approximately 72% of total value for all measured metals, followed by Pd (10%). Approximately 82% of total metal value can be recycled with current standard recycling methods for Au, Cu, Pd, Pt, which only comprise 6 wt% of the total device. The printed circuit board (pcb) contains 90% of the measured Au, 98% of Cu, 99% of Pd, 86% of In, and 93% of Ta. The Au, Pd, Cu, Pt, Ta, In, Ga contents in a smartphone pcb are significantly higher than the metal content in currently mined ores. Magnets contain 96% of the measured REE and 40% of the measured Ga, with higher concentrations than ores for REE and Ga. For Co and Ge, metal content in smartphones (w/o batteries) is lower than in ores.
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•Detailed content of 53 metals from smartphones is investigated.•Metal concentrations in smartphones are compared with currently mined ores.•Fluctuating metal prices can affect recycling efforts.•Potential recycling options and obstacles for metals in smartphones are discussed.
On Mars, seasonal martian flow features known as recurring slope lineae (RSL) are prevalent on sun-facing slopes and are associated with salts. On Earth, subsurface interactions of gypsum with ...chlorides and oxychlorine salts wreak havoc: instigating sinkholes, cave collapse, debris flows, and upheave. Here, we illustrate (i) the disruptive potential of sulfate-chloride reactions in laboratory soil crust experiments, (ii) the formation of thin films of mixed ice-liquid water “slush” at −40° to −20°C on salty Mars analog grains, (iii) how mixtures of sulfates and chlorine
salts affect their solubilities in low-temperature environments, and (iv) how these salt brines could be contributing to RSL formation on Mars. Our results demonstrate that interactions of sulfates and chlorine salts in fine-grained soils on Mars could absorb water, expand, deliquesce, cause subsidence, form crusts, disrupt surfaces, and ultimately produce landslides after dust loading on these unstable surfaces.
Pseudotachylitic breccia (PTB) occurs in a drill core from the crater floor of the 11km diameter, Proterozoic Dhala impact structure, India. PTBs were intersected in late Archean granitoids between ...348.15m and 502.55m depth in the MCB-10 drill core from the center of the Dhala structure. The breccias comprise both cataclastic-matrix as well as melt breccias. The presence of microlites and vesicles in the groundmass and a widely observed flow fabric in the PTB support the presence of melt in the groundmass of some samples. Clasts in PTB are derived from the Archean granitoid basement. PTB matrix, the matrix of impact melt breccia also occurring between 256.50m and 502.55m depth, and the target granitoids vary in terms of silica, total alkali, magnesium and iron oxide contents. Chondrite-normalized REE patterns of PTB and target granitoids are similar, but the elemental abundances in the PTB are lower. The restricted size of PTB as veins and pods of up to 2.5cm width, their occurrence at varied depths over a core length of ~150m, the clast population, and the chemical relationships between PTB and their host rocks all suggest the derivation of these breccias locally from the fractured basement granitoids involving in-situ melting. We favor that this took place due to rapid decompression during the collapse and modification stage of impact cratering, with, locally, additional energy input from frictional heating. Locally, amphibolite and dioritic mylonite occur in the host granitoids and their admixture could have contributed to the comparatively more mafic composition of PTB. Alteration of these crater floor rocks could have involved preferential reduction of silica and alkali element abundances, possibly due to impact-induced hydrothermal activity at crater floor level. This process, too, could have resulted in more mafic compositions.
•The genesis of pseudotachylitic breccias in impact structures by friction melting or other processes is controversial.•This is the first report of pseudotachylitic breccia from the 11km diameter, Proterozoic Dhala impact structure of India.•Dhala pseudotachylitic breccia occurs as both cataclasites and melt breccias within crater floor granitoid.•Melt breccias formed by in-situ melting±a friction melting component, due to rapid decompression during the collapse stage.•The entire breccia system is strongly overprinted likely in large part by impact-induced hydrothermal activity.
A versatile approach to determining the elemental content of more than 50 elements in different components of electronic devices on the example of smartphones was developed. The analytical protocol ...is based on accurate disassembly of smartphones, a single processing microwave-assisted acid digestion followed by ICP-OES and ICP-MS measurements. Method optimization and validation were performed using the certified reference material ERM®-EZ505 electronic scrap. Combined uncertainties revealed measurement uncertainty and sample heterogeneity as main contributors. The contents of up to 57 elements could be quantified in the certified reference material ERM®-EZ505 electronic scrap. The results of the certified elements Au, Be, Cu, In, Ni, Pd, and Pt overlapped within their uncertainties with the certified range and revealed recoveries of 100% ± 16%. Only Ag shows incomplete recoveries (75% ± 35%). The validated method was applied to all metal-containing components of selected smartphones, excluding batteries. The contents of up to 57 elements could be quantified and are presented exemplarily for printed circuit boards, which represent the most complex components in the investigated smartphones and thus limit the capability of the method. The ten most abundant elements in decreasing order are Cu, Fe, Si, Ni, Sn, Zn, Ba, Al, Cr, Ti, which comprise approx. 80% of the weight of the printed circuit boards. The method allows for the determination of metal content in various parts of modern smartphones, providing the basis for the estimation and prediction of future metal usage and thus the comprehensive investigation of recycling and circular economy aspects.
Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the ...Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.
Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We ...conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation.
Clay-rich sediments from the Kajjansi, Kitiko, Kitetika, and Ntawo valleys in central Uganda were analyzed for mineralogical and chemical composition, including the rare earth element (REE) contents. ...The valleys are filled with Quaternary to Recent alluvial and lacustrine sands, silt, and gravels, which formed from the bed rock metasediments of the Buganda-Toro System and from granitoid rocks that include rocks of the basement. The sediments are dominated by kaolinite and quartz, and minor phases include smectite, chlorite, and illite/muscovite. Whole rock chemistry shows that sediment samples rich in SiO2 have low Al, Fe, Sc and Cr contents. The high chemical index of alteration (CIA) values (87 to 96), chemical index of weathering (CIW) values around 98 and low contents of the alkali and alkali earth elements of the clay-rich sediments suggest a relatively more intense weathering source area. Barium, Rb, Ca, and Mg were probably flushed out by water during sedimentation. The chondrite-normalized REE patterns of the clay-rich sediments show LREE enrichments and a negative Eu anomaly. The high chondritenormalized La/Yb ratios, and Gd/Yb ratios lower than 2.0, indicate that the sediments are enriched in the LREEs and are similar to typical post-Archean shales, such as Post-Archean Australian Shale (PAAS). The mineralogical composition, REE contents, and elemental ratios in these sediments suggest a provenance from mainly felsic rocks, with only minor contributions from basic sources. The basic sediments were most likely derived from metasedimentary rocks, such as muscovite-biotite schists, which are characteristic of the Buganda-Toro System rocks, whereas the felsic sediments are derivatives of granitoid rocks of the basement. The most significant geochemical finding is that despite intense weathering, which has affected most elements, the REE, Th, and Sc remain immobile.
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