Analysis of Student Behaviour in Habitable Worlds Using Continuous Representation Visualization

We introduce a novel approach to visualizing temporal clickstream behaviour in the context of a degree-satisfying online course, Habitable Worlds, offered through Arizona State University. The current practice for visualizing behaviour within a digital learning environment has been to generate plots based on hand engineered or coded features using domain knowledge. While this approach has been effective in relating behaviour to known phenomena, features crafted from domain knowledge are not likely well suited to make unfamiliar phenomena salient and thus can preclude discovery. We introduce a methodology for organically surfacing behavioural regularities from clickstream data, conducting an expert in-the-loop hyperparameter search, and identifying anticipated as well as newly discovered patterns of behaviour. While these visualization techniques have been used before in the broader machine learning community to better understand neural networks and relationships between word vectors, we apply them to online behavioural learner data and go a step further; exploring the impact of the parameters of the model on producing tangible, non-trivial observations of behaviour that are suggestive of pedagogical improvement to the course designers and instructors. The methodology introduced in this paper led to an improved understanding of passing and non-passing student behaviour in the course and is widely applicable to other datasets of clickstream activity where investigators and stakeholders wish to organically surface principal patterns of behaviour

Comparison of mantle lithosphere beneath early Triassic kimberlite fields in Siberian craton reconstructed from deep-seated xenocrysts

Mantle xenocrysts from Early Triassic kimberlite pipes from Kharamai, Ary Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the SCLM. PT reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units: pyroxenitic Fe-rich (1-2 GPa) and Mg-rich (2-3 GPa) layers; middle with two levels of Gar -Sp pyroxenites at ∼3 and 4 -5 GPa; Ga- dunite –harzburgites ∼ 4.5-6.5 GPa subjected to Ilm-Px vein metasomatism, and a Mg-rich dunite lower part. In the Anabar shield (Ary Mastakh, Dyuken and Kuranakh fields) mantle lithosphere is composed of three large units divided into two parts: upper part with amphiboles and phlogopite; two levels of pyroxenites and eclogites at 3 and 4 GPa, and a lower part composed of refertilized dunites. Diagrams showing P- Fe#Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities. Differences of Triassic SCLM from Devonian SCLM are in simple layering; abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part, thick pyroxenite - eclogite layer and lower part depletion, heated from SCLM base to 5.0 GPa. Kharamai mantle clinopyroxenes represent three geochemical types: 1) harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; 2) lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; 3) eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary Mastakh fields show less inclined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and Sr, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe#Ol upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian -Triassic superplume, but with no signs of delamination

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

Two distinct types of eclogites from the Raspas Complex (Ecuador), which can be distinguished based on petrography and trace element geochemistry, were analyzed for their stable (Li, O) and radiogenic (Sr, Nd) isotope signature to constrain metasomatic changes due to fluid-overprinting in metabasaltic rocks at high-pressure conditions and to identify fluid sources. MORB-type eclogites are characterized by a relative LREE depletion similar to MORB. High-pressure (HP) minerals from this type of eclogite have highly variable oxygen isotope compositions (garnet: + 4.1 to + 9.8 ‰; omphacite: + 6.1 to + 11.0 ‰; phengite: 8.7 to 10.4 ‰; amphibole: 6.2 to 10.1 ‰) and generally show equilibrium oxygen isotope fractionation. Initial 87Sr/86Sr isotope ratios are also variable (0.7037-0.7063), whereas εNd130Ma values (+ 8.3 to + 11.0) are relatively similar. Sr and O isotopic compositional differences among rocks on outcrop scale, the preservation of O isotopic compositions of low-temperature altered oceanic crust, and Sr-Nd isotopic trends typical for seafloor alteration suggest inheritance from variably altered oceanic crust. However, decreasing δ7Li values (-0.5 to -12.9 ‰) with increasing Li concentrations (11-94 ppm) indicate Li isotope fractionation by diffusion related to fluid-rock interaction. Li isotopes prove to be a very sensitive tracer of metasomatism, although the small effects on the Sr-Nd-O isotope systems suggest that the fluid-induced metasomatic event in the MORB-type eclogites was small-scale at low-water/rock ratios. This metasomatic fluid is thought to predominantly derive from in situ dehydration of MORB-type rocks. Zoisite eclogites, the second eclogite type from the Raspas Complex, are characterized by the presence of zoisite and enrichment in many incompatible trace elements compared to the MORB-type eclogites. The zoisite eclogites have a homogenous Sr-Nd isotopic signature (Initial 87Sr/86Sr = 0.7075-0.7081, εNd130Ma = -6.7 to -8.7), interpreted to reflect a metasomatic overprint. The isotopic signature can be attributed to the metasomatic formation of zoisite because associated zoisite veins are isotopically similar. Relatively homogenous O isotope values for garnet (10.9-12.3 ‰) omphacite (9.4 to 10.8 ‰), amphibole (10.0-10.1 ‰) and zoisite (10.5-11.9 ‰) and inter-mineral O isotopic disequilibria are consistent with a metasomatic overprint via open-system fluid input. Li concentrations (46-76 ppm) and δ7Li values of the zoisite eclogites overlap the range of the MORB-type eclogites. The large amount of fluid required for isotopic homogenization, combined with the results from fluid inclusion studies, suggests that deserpentinization played a major role in generating the metasomatic fluid that altered the zoisite eclogites. However, influence of a (meta)sedimentary source is required based on Sr-Nd isotope data and trace element enrichments. The significant geochemical variation in the various eclogites generated by interaction with metasomatic fluids has to be considered in attempts to constrain recycling at convergent margins

Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes

Eclogites from the Tian Shan high-pressure/low-temperature (HP/LT) metamorphic belt show evidence for successively increasing metasomatic alteration with increasing retrograde, blueschist-facies overprint. To constrain the source(s) of the metasomatizing fluid and to evaluate elemental and isotopic changes during this overprint, two sequences of eclogite-blueschist transitions were investigated: A layered transition from eclogite to blueschist (FTS 9–1 sequence) and blueschist-facies overprinted pillow metabasalts (FTS 4 samples). Geochemical trends based on the relationships of K, Ba, Rb and Th are consistent with HP metasomatism, but distinct from typical seafloor alteration trends. In contrast, oxygen isotope ratios in garnet (δ18OV-SMOW = 7.3–8.7‰) and omphacite (δ18OV-SMOW = 8.2–9.7‰) are similar to δ18OV-SMOW in bulk low-temperature altered oceanic crust (AOC), suggesting O isotopic preservation of a seafloor alteration signature. Carbonate crystallization related to the metasomatic overprint demonstrate CO2 mobility during subduction and potential C storage in HP metamorphic rocks. Carbon isotope ratios in the two sequences differ markedly: Disseminated calcite in the layered FTS 9–1 sequence has δ13CV-PDB = − 9.14 ± 0.19‰, whereas vein-forming ankerite in the pillow metabasalts has δ13CV-PDB = − 2.08 ± 0.12‰. The ankerite reflects an inorganic marine/hydrothermal signature, as observed in ophiolites, whereas the low δ13CV-PDB values from the calcite point to a contribution of organic carbon. The time when the metasomatic overprint occurred is estimated to be ~ 320 ± 11 Ma based on a Rb-Sr isochron age of six blueschist samples from the pillow metabasalts, which is in agreement with active subduction in this region. Initial (T = 320 Ma) 87Sr/86Sr ratios for all HP/LT rocks range from 0.7059 – 0.7085, and εNd320Ma varies from − 0.4 to + 10.9. Both eclogite-blueschist sequences have initial Sr isotope compositions (87Sr/86Sr ~ 0.707) that are significantly higher than those of typical oceanic mantle-derived basalts. They are thought to derive from a fluid that preserved the Sr isotopic signature of seawater by fluid-rock interaction with seawater-altered oceanic lithosphere in a subduction channel. Mixing models between eclogite and various fluids suggest that the contribution of a sediment-derived fluid was likely less than 20%. A fluid predominantly derived from seawater-altered oceanic lithosphere is also supported by the calculated O isotope composition of the fluids (10.2 – 11.2‰). It is thus evident that subduction channel fluids carry complex, mixed elemental and isotopic signatures, which reflect the composition of their source rocks modified by interaction with various other lithologies. Highlights ► Eclogites from the Tian Shan show blueschist-facies metasomatic overprint ► Fluid-induced metasomatism occurred at 320 ± 11 Ma ► Fluid predominantly derived from seawater-altered oceanic lithosphere ► Carbonates reflect C sequestration of mixture of organic and inorganic component

The potential science and engineering value of samples delivered to Earth by Mars sample return

© The Meteoritical Society, 2019. Executive Summary: Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re-evaluate and update the sample-related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub-objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub-Objectives for MSR Identified by iMOST: Objective 1 Interpret the primary geologic processes and history that formed the Martian geologic record, with an emphasis on the role of water. Intent To investigate the geologic environment(s) represented at the Mars 2020 landing site, provide definitive geologic context for collected samples, and detail any characteristics that might relate to past biologic processesThis objective is divided into five sub-objectives that would apply at different landing sites. 1.1 Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. Intent To understand the preserved Martian sedimentary record. Samples A suite of sedimentary rocks that span the range of variation. Importance Basic inputs into the history of water, climate change, and the possibility of life 1.2 Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. Intent To evaluate at least one potentially life-bearing “habitable” environment Samples A suite of rocks formed and/or altered by hydrothermal fluids. Importance Identification of a potentially habitable geochemical environment with high preservation potential. 1.3 Understand the rocks and minerals representative of a deep subsurface groundwater environment. Intent To evaluate definitively the role of water in the subsurface. Samples Suites of rocks/veins representing water/rock interaction in the subsurface. Importance May constitute the longest-lived habitable environments and a key to the hydrologic cycle. 1.4 Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. Intent To constrain time-variable factors necessary to preserve records of microbial life. Samples Regolith, paleosols, and evaporites. Importance Subaerial near-surface processes could support and preserve microbial life. 1.5 Determine the petrogenesis of Martian igneous rocks in time and space. Intent To provide definitive characterization of igneous rocks on Mars. Samples Diverse suites of ancient igneous rocks. Importance Thermochemical record of the planet and nature of the interior. Objective 2 Assess and interpret the potential biological history of Mars, including assaying returned samples for the evidence of life. Intent To investigate the nature and extent of Martian habitability, the conditions and processes that supported or challenged life, how different environments might have influenced the preservation of biosignatures and created nonbiological “mimics,” and to look for biosignatures of past or present life.This objective has three sub-objectives: 2.1 Assess and characterize carbon, including possible organic and pre-biotic chemistry. Samples All samples collected as part of Objective 1. Importance Any biologic molecular scaffolding on Mars would likely be carbon-based. 2.2 Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. Samples All samples collected as part of Objective 1. Importance Provides the means of discovering ancient life. 2.3 Assess the possibility that any life forms detected are alive, or were recently alive. Samples All samples collected as part of Objective 1. Importance Planetary protection, and arguably the most important scientific discovery possible. Objective 3 Quantitatively determine the evolutionary timeline of Mars. Intent To provide a radioisotope-based time scale for major events, including magmatic, tectonic, fluvial, and impact events, and the formation of major sedimentary deposits and geomorphological features. Samples Ancient igneous rocks that bound critical stratigraphic intervals or correlate with crater-dated surfaces. Importance Quantification of Martian geologic history. Objective 4 Constrain the inventory of Martian volatiles as a function of geologic time and determine the ways in which these volatiles have interacted with Mars as a geologic system. Intent To recognize and quantify the major roles that volatiles (in the atmosphere and in the hydrosphere) play in Martian geologic and possibly biologic evolution. Samples Current atmospheric gas, ancient atmospheric gas trapped in older rocks, and minerals that equilibrated with the ancient atmosphere. Importance Key to understanding climate and environmental evolution. Objective 5 Reconstruct the processes that have affected the origin and modification of the interior, including the crust, mantle, core and the evolution of the Martian dynamo. Intent To quantify processes that have shaped the planet's crust and underlying structure, including planetary differentiation, core segregation and state of the magnetic dynamo, and cratering. Samples Igneous, potentially magnetized rocks (both igneous and sedimentary) and impact-generated samples. Importance Elucidate fundamental processes for comparative planetology. Objective 6 Understand and quantify the potential Martian environmental hazards to future human exploration and the terrestrial biosphere. Intent To define and mitigate an array of health risks related to the Martian environment associated with the potential future human exploration of Mars. Samples Fine-grained dust and regolith samples. Importance Key input to planetary protection planning and astronaut health. Objective 7 Evaluate the type and distribution of in-situ resources to support potential future Mars exploration. Intent To quantify the potential for obtaining Martian resources, including use of Martian materials as a source of water for human consumption, fuel production, building fabrication, and agriculture. Samples Regolith. Importance Production of simulants that will facilitate long-term human presence on Mars. Summary of iMOST Findings: Several specific findings were identified during the iMOST study. While they are not explicit recommendations, we suggest that they should serve as guidelines for future decision making regarding planning of potential future MSR missions. The samples to be collected by the Mars 2020 (M-2020) rover will be of sufficient size and quality to address and solve a wide variety of scientific questions. Samples, by definition, are a statistical representation of a larger entity. Our ability to interpret the source geologic units and processes by studying sample sub sets is highly dependent on the quality of the sample context. In the case of the M-2020 samples, the context is expected to be excellent, and at multiple scales. (A) Regional and planetary context will be established by the on-going work of the multi-agency fleet of Mars orbiters. (B) Local context will be established at field area- to outcrop- to hand sample- to hand lens scale using the instruments carried by M-2020. A significant fraction of the value of the MSR sample collection would come from its organization into sample suites, which are small groupings of samples designed to represent key aspects of geologic or geochemical variation. If the Mars 2020 rover acquires a scientifically well-chosen set of samples, with sufficient geological diversity, and if those samples were returned to Earth, then major progress can be expected on all seven of the objectives proposed in this study, regardless of the final choice of landing site. The specifics of which parts of Objective 1 could be achieved would be different at each of the final three candidate landing sites, but some combination of critically important progress could be made at any of them. An aspect of the search for evidence of life is that we do not know in advance how evidence for Martian life would be preserved in the geologic record. In order for the returned samples to be most useful for both understanding geologic processes (Objective 1) and the search for life (Objective 2), the sample collection should contain BOTH typical and unusual samples from the rock units explored. This consideration should be incorporated into sample selection and the design of the suites. The retrieval missions of a MSR campaign should (1) minimize stray magnetic fields to which the samples would be exposed and carry a magnetic witness plate to record exposure, (2) collect and return atmospheric gas sample(s), and (3) collect additional dust and/or regolith sample mass if possible

Contributing Factors to Ice Mass Loss on Himalayan Debris-Covered Glaciers

Despite being heavily covered in debris, glaciers of the Himalaya have undergone and continue to undergo major losses of ice volume. This occurs not so much by loss of area, but more from a reduction in the thickness of the glacier at average rates that locally can exceed 1 m/year. This dissertation makes use of cartographic, photographic, and field data from the Tibetan Plateau and Ngozumpa, one of Nepal\u27s largest and longest glaciers, towards determining and quantifying factors that influence glacial ice loss in the high Himalaya. Volume estimates, using historical maps and archival/modern-day expedition photos, show glacial loss of 3.7±0.6 cubic km total for four major glaciers in Tibet. Over 100-meter ice height losses are observed from lateral moraine to glacier surface in some locations. This is similar to the losses found in the southern (Nepalese) Himalaya, despite the smaller mean-illumination angle of glaciers flowing northward and the rain-shadow geographical setting. The presence of supraglacial lakes can accelerate vertical ice mass loss. From time-lapse photography, small ponds in the mid-ablation zone on Ngozumpa were found to have different growth patterns: evaporation and/or infiltration of water through the underlying substrate; expansion through large calving events; and multiple fills, drains and refills, providing evidence for connections made to the englacial/subglacial system. Lake floor deepening rate on Spillway, a large supraglacial lake on Ngozumpa, is important to quantify, as the lake\u27s growth presents a flooding hazard to Sherpa villages down-valley. Sonar data provide detail on lake floor substrates, distinguishing mud, rock, and bare ice. In areas of fast deepening where low mean bottom temperatures prevail, thin debris cover or bare ice is encountered. This finding is consistent with previously reported localized regions of lake deepening, and is useful in predicting future growth. Impurities in snow and ice at the higher altitudes can lead to decreases in albedo and, thus, accelerated melting in glacier accumulation zones. Snow samples were collected from 4800 - 6100 m.a.s.l. in valleys of eastern and western Nepal. Downwind of villages, black carbon was found to be the dominant contaminant, while for more remote glaciers further up-valley, dust prevails

Thermal and Physical Investigations into Lake Deepening Processes on Spillway Lake, Ngozumpa Glacier, Nepal

This paper investigates physical processes in the four sub-basins of Ngozumpa glacier’s terminal Spillway Lake for the period 2012–2014 in order to characterize lake deepening and mass transfer processes. Quantifying the growth and deepening of this terminal lake is important given its close vicinity to Sherpa villages down-valley. To this end, the following are examined: annual, daily and hourly temperature variations in the water column, vertical turbidity variations and water level changes and map lake floor sediment properties and lake floor structure using open water side-scan sonar transects. Roughness and hardness maps from sonar returns reveal lake floor substrates ranging from mud, to rocky debris and, in places, bare ice. Heat conduction equations using annual lake bottom temperatures and sediment properties are used to calculate bottom ice melt rates (lake floor deepening) for 0.01 to 1-m debris thicknesses. In areas of rapid deepening, where low mean bottom temperatures prevail, thin debris cover or bare ice is present. This finding is consistent with previously reported localized regions of lake deepening and is useful in predicting future deepening