Dynamic Compressive Strength and Fragmentation in Felsic Crystalline Rocks

Brittle deformation in rocks depends upon loading rate; with increasing rates, typically greater than ~102 s‐1, rocks become significantly stronger and undergo increasingly severe fragmentation. Dynamic conditions required for rate‐dependent brittle failure may be reached during impact events, seismogenic rupture, and landslides. Material characteristics and fragment characterization of specific geomaterials from dynamic loading are only approximately known. Here we determine the characteristic strain rate for dynamic behavior in felsic crystalline rocks, including anisotropy, and describe the resulting fragments. Regardless of the type of felsic crystalline rock or anisotropy, the characteristic strain rate is the same within uncertainties for all tested materials, with an average value of 229 ± 81 s‐1. Despite the lack of variation of the critical strain rate with lithology, we find that the degree of fragmentation as a function of strain rate varies depending on material. Scaled or not, the fragmentation results are inconsistent with current theoretical models of fragmentation. Additionally, we demonstrate that conditions during impact cratering, where the impactor diameter is less than ~100 m, are analogous to the experiments carried out here, and therefore that dynamic strengthening and compressive fragmentation should be considered as important processes during impact cratering

Spatial Guilds in the Serengeti Food Web Revealed by a Bayesian Group Model

Food webs, networks of feeding relationships among organisms, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. Despite long-standing interest in the compartmental structure of food webs, past network analyses of food webs have been constrained by a standard definition of compartments, or modules, that requires many links within compartments and few links between them. Empirical analyses have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure in food webs using a flexible definition of a group that can describe both functional roles and standard compartments. The Serengeti ecosystem provides an opportunity to examine structure in a newly compiled food web that includes species-level resolution among plants, allowing us to address whether groups in the food web correspond to tightly-connected compartments or functional groups, and whether network structure reflects spatial or trophic organization, or a combination of the two. We have compiled the major mammalian and plant components of the Serengeti food web from published literature, and we infer its group structure using our method. We find that network structure corresponds to spatially distinct plant groups coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial patterns, in contrast to the standard compartments typically identified in ecological networks. From data consisting only of nodes and links, the group structure that emerges supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence.Comment: 28 pages, 6 figures (+ 3 supporting), 2 tables (+ 4 supporting

Gene content evolution in the arthropods

Arthropods comprise the largest and most diverse phylum on Earth and play vital roles in nearly every ecosystem. Their diversity stems in part from variations on a conserved body plan, resulting from and recorded in adaptive changes in the genome. Dissection of the genomic record of sequence change enables broad questions regarding genome evolution to be addressed, even across hyper-diverse taxa within arthropods. Using 76 whole genome sequences representing 21 orders spanning more than 500 million years of arthropod evolution, we document changes in gene and protein domain content and provide temporal and phylogenetic context for interpreting these innovations. We identify many novel gene families that arose early in the evolution of arthropods and during the diversification of insects into modern orders. We reveal unexpected variation in patterns of DNA methylation across arthropods and examples of gene family and protein domain evolution coincident with the appearance of notable phenotypic and physiological adaptations such as flight, metamorphosis, sociality, and chemoperception. These analyses demonstrate how large-scale comparative genomics can provide broad new insights into the genotype to phenotype map and generate testable hypotheses about the evolution of animal diversity

Ocean Drilling Perspectives on Meteorite Impacts

Extraterrestrial impacts that reshape the surfaces of rocky bodies are ubiquitous in the solar system. On early Earth, impact structures may have nurtured the evolution of life. More recently, a large meteorite impact off the Yucatán Peninsula in Mexico at the end of the Cretaceous caused the disappearance of 75% of species known from the fossil record, including non-avian dinosaurs, and cleared the way for the dominance of mammals and the eventual evolution of humans. Understanding the fundamental processes associated with impact events is critical to understanding the history of life on Earth, and the potential for life in our solar system and beyond. Scientific ocean drilling has generated a large amount of unique data on impact pro- cesses. In particular, the Yucatán Chicxulub impact is the single largest and most sig- nificant impact event that can be studied by sampling in modern ocean basins, and marine sediment cores have been instrumental in quantifying its environmental, cli- matological, and biological effects. Drilling in the Chicxulub crater has significantly advanced our understanding of fundamental impact processes, notably the formation of peak rings in large impact craters, but these data have also raised new questions to be addressed with future drilling. Within the Chicxulub crater, the nature and thickness of the melt sheet in the central basin is unknown, and an expanded Paleocene hemipelagic section would provide insights to both the recovery of life and the climatic changes that followed the impact. Globally, new cores collected from today’s central Pacific could directly sample the downrange ejecta of this northeast-southwest trending impact. Extraterrestrial impacts have been controversially suggested as primary drivers for many important paleoclimatic and environmental events throughout Earth history. However, marine sediment archives collected via scientific ocean drilling and geo- chemical proxies (e.g., osmium isotopes) provide a long-term archive of major impact events in recent Earth history and show that, other than the end-Cretaceous, impacts do not appear to drive significant environmental changes

Sphene Emotional: How Titanite Was Shocked When the Dinosaurs Died

Accessory mineral geochronometers such as zircon, monazite, baddeleyite, and xenotime are increasingly being recognized for their ability to preserve diagnostic microstructural evidence of hypervelocity processes. However, little is known about the response of titanite to shock metamorphism, even though it is a widespread accessory phase and U-Pb geochronometer. Here we report two new mechanical twin modes in titanite within shocked granitoids from the Chicxulub impact structure, Mexico. Titanite grains in the newly acquired International Ocean Discovery Program Site expedition 364 M0077A core preserve multiple sets of polysynthetic twins, most commonly with composition planes (K1), = ~{111}, and shear direction (1) = , and less commonly with the mode K1 = {130}, 1 = ~. In some grains, {130} deformation bands have formed concurrently with shock twins, indicating dislocation glide with Burgers vector b = [341] can be active at shock conditions. Twinning of titanite in these modes, the presence of planar deformation features in shocked quartz, and lack of diagnostic shock microstructures in zircon in the same samples highlights the utility of titanite as a shock indicator for a shock pressure range between ~12 and ~17 GPa. Given the challenges of identifying ancient impact evidence on Earth and other bodies, microstructural analysis of titanite is here demonstrated to be a new avenue for recognizing impact deformation in materials where other impact evidence may be erased, altered, or did not manifest due to low shock pressure

Probing the hydrothermal system of the Chicxulub impact crater

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years

Brown marmorated stink bug, Halyomorpha halys (Stål), genome: putative underpinnings of polyphagy, insecticide resistance potential and biology of a top worldwide pest

Background Halyomorpha halys (Stål), the brown marmorated stink bug, is a highly invasive insect species due in part to its exceptionally high levels of polyphagy. This species is also a nuisance due to overwintering in human-made structures. It has caused significant agricultural losses in recent years along the Atlantic seaboard of North America and in continental Europe. Genomic resources will assist with determining the molecular basis for this species’ feeding and habitat traits, defining potential targets for pest management strategies. Results Analysis of the 1.15-Gb draft genome assembly has identified a wide variety of genetic elements underpinning the biological characteristics of this formidable pest species, encompassing the roles of sensory functions, digestion, immunity, detoxification and development, all of which likely support H. halys’ capacity for invasiveness. Many of the genes identified herein have potential for biomolecular pesticide applications. Conclusions Availability of the H. halys genome sequence will be useful for the development of environmentally friendly biomolecular pesticides to be applied in concert with more traditional, synthetic chemical-based controls

Genome of the Asian Longhorned Beetle (\u3cem\u3eAnoplophora glabripennis\u3c/em\u3e), a Globally Significant Invasive Species, Reveals Key Functional and Evolutionary Innovations at the Beetle-Plant Interface

Background: Relatively little is known about the genomic basis and evolution of wood-feeding in beetles. We undertook genome sequencing and annotation, gene expression assays, studies of plant cell wall degrading enzymes, and other functional and comparative studies of the Asian longhorned beetle, Anoplophora glabripennis, a globally significant invasive species capable of inflicting severe feeding damage on many important tree species. Complementary studies of genes encoding enzymes involved in digestion of woody plant tissues or detoxification of plant allelochemicals were undertaken with the genomes of 14 additional insects, including the newly sequenced emerald ash borer and bull-headed dung beetle. Results: The Asian longhorned beetle genome encodes a uniquely diverse arsenal of enzymes that can degrade the main polysaccharide networks in plant cell walls, detoxify plant allelochemicals, and otherwise facilitate feeding on woody plants. It has the metabolic plasticity needed to feed on diverse plant species, contributing to its highly invasive nature. Large expansions of chemosensory genes involved in the reception of pheromones and plant kairomones are consistent with the complexity of chemical cues it uses to find host plants and mates. Conclusions: Amplification and functional divergence of genes associated with specialized feeding on plants, including genes originally obtained via horizontal gene transfer from fungi and bacteria, contributed to the addition, expansion, and enhancement of the metabolic repertoire of the Asian longhorned beetle, certain other phytophagous beetles, and to a lesser degree, other phytophagous insects. Our results thus begin to establish a genomic basis for the evolutionary success of beetles on plants

Die Untergrundstruktur schiefwinkliger Impaktkrater

In this thesis, several terrestrial and Martian impact craters were the subject of detailed structural field and remote sensing analysis, with a strong focus on structural deformation related to oblique impacts. Additional microstructural analysis of shear induced features in quartz grains from samples of several impact structures was performed and their role as shock metamorphic features was evaluated. At Wolfe Creek crater, Australia, the hypothesis is tested that the asymmetrical, non-radial distribution of the ejecta blanket commonly seen in oblique impacts on other planets can be followed back to an internal structural signal of deformed rock beds in terrestrial crater rims (chapter 2). This non-radial signal in Wolfe Creek is used to infer the direction of impact. For comparison, the results of Wolfe Creek crater are tested on a second terrestrial crater, Meteor Crater in Arizona, USA (chapter 3). The evaluation of bedding data from Meteor Crater shows that the expected signal of an oblique impact is weak and has been overprinted by deformational effects caused by the pre-impact target heterogeneities. These deformational features are observed in detail, and mechanisms of their generation are suggested that solidify the proposed connection of Meteor Crater’s polygonal shape to target heterogeneities. Based on recent discoveries of central peaks that display non-radial structural deformation, detailed mapping of the Matt Wilson impact structure, Australia, is performed (chapter 4). Mapping results reveal that Matt Wilson is the first elliptical crater found on Earth with a central uplift. The structural deformation of the central uplift is strongly non-radial and displays a preferred direction of thrusting and imbrication that coincides with the long axis of the eroded elliptical rim. Thus, two independent indicators of non- radial deformation which infer an impact direction are found in the same impact structure. The central uplift of Martin Crater, Mars, is structurally mapped (chapter 5). Results show that the orientation of structural deformation is at a ~180° angle to the direction of impact inferred by the ejecta blanket. Recently published numerical models are used to devise a model for asymmetrical central uplift formation based on a chain of events initiated by oblique impact, and the relationship of the orientation of structural deformation to the impact direction is discussed. Initiated by microstructural analysis of samples collected from the Matt Wilson impact structure, a recently discovered type of planar microstructure in quartz, termed “feather features”, is systematically analysed in samples from several impact craters (chapter 6). Feather features are shear induced structures that are formed by shock metamorphic deformation of quartz in low-shock pressure regimes, and give insights into the differential stresses that occur during the passage of the shock wave in the early stages of crater formation. Their use as indicators for impact craters is suggested.In dieser Dissertation wurden sowohl mehrere terrestrische als auch Mars- Krater Gegenstand detaillierter struktureller Gelände- und Fernerkundungsanalysen, wobei der Fokus auf struktureller Deformation schiefwinkliger Einschläge liegt. Zusätzliche mikrostrukturelle Analysen scherinduzierter Strukturen in Quarzkörnern aus Proben verschiedener Impaktstrukturen wurden durchgeführt, und ihre Bedeutung als stoßwellenmetamorphe Strukturen wurde evaluiert. In Wolfe Creek, Australien, wird die Hypothese getestet, ob die asymmetrische, nicht-radiale Verteilung der Ejektadecke zu einem internen strukturellen Signal des deformierten Gesteins in Kraterrändern zurückverfolgt werden kann (Kapitel 2). Das resultierende, nicht-radiale Signal in Wolfe Creek wurde benutzt, um eine Einschlagsrichtung anzugeben. Die Ergebnisse von Wolfe Creek wurden an Meteor Krater in Arizona, USA geprüft (Kapitel 3). Die Evaluierung der Schichtwerte vom Meteor Krater zeigt, dass das erwartete Signal eines schiefwinkligen Einschlags nicht ausreichend detektierbar ist, und von präimpakt- Targetheterogenitäten überprägt wurde. Diese Deformationsstrukturen sind im Detail untersucht worden. Mechanismen ihrer Generierung sind vorgeschlagen worden, die einen Zusammenhang zwischen der polygonalen Form des Kraterrands und der Targetheterogenitäten herstellen. Eine detaillierte strukturelle Kartierung der Matt Wilson Impaktstruktur wurde durchgeführt (Kapitel 4). Kartierergebnisse zeigen, dass Matt Wilson der erste elliptische Krater der Erde ist, der eine Zentralaufwölbung aufweist. Die strukturelle Deformation der Zentralaufwölbung ist nicht-radial ausgerichtet. Ihre Überschiebungs- und Verschuppungsrichtung zeigt eine Vorzugsrichtung, die mit der langen Achse des elliptischen Kraterrandes übereinstimmt, d.h. zwei unabhängige Indikatoren nichtradialer Deformation sind in einer Impaktstruktur gefunden wurden, die die Einschlagsrichtung anzeigen. Die Zentralaufwölbung des Martin-Kraters auf dem Mars ist kartiert worden (Kapitel 5). Die Ergebnisse zeigen, dass die Ausrichtung der strukturellen Deformation in einem ~180° Winkel zur durch die Ejektadecke angezeigten Einschlagsrichtung steht. Jüngst publizierte numerische Modellierungen wurden verwendet, um ein Modell asymmetrischer Zentralbergsaufwölbung zu erarbeiten, die auf einer Kette von Ereignissen basiert, welche durch einen schiefwinkligen Einschlag eingeleitet wurden. Eine jüngst entdeckte Art planarer Mikrostrukturen in Quarz, die als „feather features“ oder „Federelemente“ bezeichnet werden, wurden systematisch in Proben mehrerer Impaktstrukturen analysiert (Kapitel 6). Federelemente sind scherinduzierte Strukturen, die durch stoßwellenmetamorphe Deformation von Quarz im Niedrigstoßwellen-Druckregime gebildet werden. Sie geben Einsichten in die differentiellen Spannungen, die während des Durchlaufs der Stoßwellen in den frühen Phasen der Kraterbildung auftreten. Ihr Nutzen als Impaktindikatoren wird vorgeschlagen