Estimates of the average composition of various Precambrian shields and a variety of estimates of the average composition of upper continental crust show considerable disagreement for a number of ...trace elements, including Ti, Nb, Ta, Cs, Cr, Ni, V, and Co. For these elements and others that are carried predominantly in terrigenous sediment, rather than in solution (and ultimately into chemical sediment), during the erosion of continents the La/element ratio is relatively uniform in clastic sediments. Since the average rare earth element (REE) pattern of terrigenous sediment is widely accepted to reflect the upper continental crust, such correlations provide robust estimates of upper crustal abundances for these trace elements directly from the sedimentary data. Suggested revisions to the upper crustal abundances of Taylor and McLennan 1985 are as follows (all in parts per million): Sc = 13.6, Ti = 4100, V = 107, Cr = 83, Co = 17, Ni = 44, Nb = 12, Cs = 4.6, Ta = 1.0, and Pb = 17. The upper crustal abundances of Rb, Zr, Ba, Hf, and Th were also directly reevaluated and K, U, and Rb indirectly evaluated (by assuming Th/U, K/U, and K/Rb ratios), and no revisions are warranted for these elements. In the models of crustal composition proposed by Taylor and McLennan 1985 the lower continental crust (75% of the entire crust) is determined by subtraction of the upper crust (25%) from a model composition for the bulk crust, and accordingly, these changes also necessitate revisions to lower crustal abundances for these elements.
The Sedimentary Cycle on Early Mars McLennan, Scott M; Grotzinger, John P; Hurowitz, Joel A ...
Annual review of earth and planetary sciences,
05/2019, Letnik:
47, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Two decades of intensive research have demonstrated that early Mars (
2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink ...framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars' sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record.
Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record.
Mars' ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions.
Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages.
Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed.
Sulfate-dominated sedimentary deposits are widespread on the surface of Mars, which contrasts with the rarity of carbonate deposits, and indicates surface waters with chemical features drastically ...different from those on Earth. While the Earth’s surface chemistry and climate are intimately tied to the carbon cycle, it is the sulfur cycle that most strongly influences the Martian geosystems. The presence of sulfate minerals observed from orbit and in-situ via surface exploration within sedimentary rocks and unconsolidated regolith traces a history of post-Noachian aqueous processes mediated by sulfur. These materials likely formed in water-limited aqueous conditions compared to environments indicated by clay minerals and localized carbonates that formed in surface and subsurface settings on early Mars. Constraining the timing of sulfur delivery to the Martian exosphere, as well as volcanogenic H
2
O is therefore central, as it combines with volcanogenic sulfur to produce acidic fluids and ice. Here, we reassess and review the Martian geochemical reservoirs of sulfur from the innermost core, to the mantle, crust, and surficial sediments. The recognized occurrences and the mineralogical features of sedimentary sulfate deposits are synthesized and summarized. Existing models of formation of sedimentary sulfate are discussed and related to weathering processes and chemical conditions of surface waters. We also review existing models of sulfur content in the Martian mantle and analyze how volcanic activities may have transferred igneous sulfur into the exosphere and evaluate the mass transfers and speciation relationships between volcanic sulfur and sedimentary sulfates. The sedimentary clay-sulfate succession can be reconciled with a continuous volcanic eruption rate throughout the Noachian-Hesperian, but a process occurring around the mid-Noachian must have profoundly changed the composition of volcanic degassing. A hypothetical increase in the oxidation state or in water content of Martian lavas or a decrease in atmospheric pressure is necessary to account for such a change in composition of volcanic gases. This would allow the pre mid-Noachian volcanic gases to be dominated by water and carbon-species but late Noachian and Hesperian volcanic gases to be sulfur-rich and characterized by high SO
2
content. Interruption of early dynamo and impact ejection of the atmosphere may have decreased the atmospheric pressure during the early Noachian whereas it remains unclear how the redox state or water content of lavas could have changed. Nevertheless, volcanic emission of SO
2
rich gases since the late Noachian can explain many features of Martian sulfate-rich regolith, including the mass of sulfate and the particular chemical features (i.e. acidity) of surface waters accompanying these deposits. How SO
2
impacted on Mars’s climate, with possible short time scale global warming and long time scale cooling effects, remains controversial. However, the ancient wet and warm era on Mars seems incompatible with elevated atmospheric sulfur dioxide because conditions favorable to volcanic SO
2
degassing were most likely not in place at this time.
Background/Objectives
Previous studies have demonstrated an increased prevalence of inflammatory bowel disease (IBD) in adults with hidradenitis suppurativa (HS). Whether the same association exists ...in pediatric patients is unknown. Fecal calprotectin (FC) is used to screen and monitor disease activity in IBD. There are no data on using FC to screen for IBD in pediatric patients with HS. Study objectives include a) assessing the prevalence of IBD among pediatric patients with HS; b) characterizing the IBD phenotype among pediatric patients with HS; and c) describing the use of FC as a screening tool for IBD in this population.
Design/Methods
This retrospective chart review was conducted at a single academic children's hospital. We included patients ≤18 years old diagnosed with HS between 2013 and 2018.
Results
We identified 109 pediatric patients with HS. Six patients (6/109, 5.5%) were diagnosed with IBD, 83.3% (5/6) classified as ulcerative colitis. Almost half (53/109, 48.6%) of HS patients had gastrointestinal symptoms; of those, 11.3% (6/53) were diagnosed with IBD. FC was obtained in 8.3% (9/109) of HS patients overall and 66.7% (4/6) of HS patients diagnosed with IBD. Among patients with gastrointestinal symptoms, FC was obtained in 17.0% (9/53); endoscopy was performed in 24.5% (13/53). FC was elevated in all patients with IBD with an FC level. Of those with elevated FC, 80.0% (4/5) had IBD.
Conclusions
Pediatric HS may be associated with an increased prevalence of IBD suggesting that more widespread screening for IBD may be indicated. FC is infrequently used but may be a useful screening tool.
We have observed both minor‐arc (R1) and major‐arc (R2) Rayleigh waves for the largest marsquake (magnitude of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show ...that a simple, two‐layer model with an interface located at 21–29 km and an upper crustal shear‐wave velocity of 3.05–3.17 km/s can fit the group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models constrained from gravity data and upper crustal shear‐wave velocities of 2.61–3.27 and 3.28–3.52 km/s in the lowlands and highlands, respectively. The shear‐wave velocity being faster in the highlands than in the lowlands indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.
Plain Language Summary
The largest marsquake ever recorded occurred recently and waves propagating at the surface, called surface waves, have been observed. Owing to the relatively large magnitude (i.e., 4.7 ± 0.2) of this event, surface wave energy is still clearly visible after one orbit around the red planet. The shortest path taken by the wave propagating between the source and the receiver is located in the northern lowlands, near the boundary with the southern highlands (called dichotomy). The surface wave traveling in the opposite direction, following the longer distance between the quake and the seismic station, mostly passes through the highlands. Analyses of these two paths reveal that the average shear‐wave velocity is faster in the highlands than in the lowlands near the dichotomy boundary. This lower velocity in the lowlands may be due to the presence of thick accumulations of sedimentary rocks and relatively higher porosity.
Key Points
Analyses of the minor‐arc and major‐arc Rayleigh waves reveal different Martian crustal structures across the dichotomy boundary
The average shear‐wave velocity is faster in the highlands than in the lowlands near the dichotomy boundary
The lower shear‐wave velocity in the lowlands may be due to the presence of sedimentary rocks and relatively higher porosity
The shallow crustal structure of Mars records the evolutionary history of the planet, which is crucial for understanding the early Martian geological environment. Until now, seismic constraints on ...the Martian crust have come primarily from the receiver functions (RFs). However, analysis of the Mars RFs did not focus on the shallow structure (1–5 km) so far due to the limitation of the signal‐to‐noise ratio at high frequencies for most events. Here, we take advantage of the S1222a and six other marsquakes, which exhibit high signal‐to‐noise ratios, to probe the shallow structure of Mars. We observe a converted S‐wave at approximately 1 s after the direct P‐wave in the high‐frequency P‐wave RFs. This suggests a discontinutity at 2‐km depth between highly fractured and more coherent crustal materials.
Plain Language Summary
The Martian shallow crustal structure is essential for understanding the geological evolution of Mars. The InSight lander successfully deployed a seismic station on Mars in late 2018, aiming to investigate the internal structure of Mars. Since most marsquakes detected previously have a low signal‐to‐noise ratio (SNR) at high frequencies, most seismic analyses do not focus on the shallow structure of Mars (1–5 km). However, when the InSight seismometer was near the end of its observational lifetime, a large marsquake occurred on sol 1222 with significant high‐frequency energy, far more than the noise level, allowing us to study the Martian shallow structure. We calculate the high‐frequency P‐wave receiver function (RF) of S1222a and extract a converted S‐wave at approximately 1 s after the direct P‐wave. To confirm the result, we also compute P‐wave RFs for high SNR events that occurred before. We observe this ∼1‐s signal in the high‐frequency P‐wave RFs of two additional large events as well. Combined with the geological analysis adjacent to the InSight lander, we attribute this 1‐s converted S‐wave to a discontinuity at approximately 2 km depth, probably corresponding to the bottom of highly fractured crustal materials beneath the InSight landing site.
Key Points
We calculate high‐frequency P‐wave receiver functions (RF) from InSight seismic data of seven marsquakes with high signal‐to‐noise ratios
The high‐frequency RFs exhibit a converted S‐wave at approximately 1 s
The ∼1‐s converted S‐wave suggests a discontinuity at a depth of approximately 2 km beneath the InSight lander
Planetary Crusts Taylor, S. Ross; McLennan, Scott
12/2008, Letnik:
v.Series Number 10
eBook
Planetary Crusts explains how and why solid planets and satellites develop crusts. Extensively referenced and annotated, it presents a geochemical and geological survey of the crusts of the Moon, ...Mercury, Venus, Earth and Mars, the asteroid Vesta, and several satellites like Io, Europa, Ganymede, Titan and Callisto. After describing the nature and formation of solar system bodies, the book presents a comparative investigation of different planetary crusts and discusses many crustal controversies. The authors propose the theory of stochastic processes dominating crustal development, and debate the possibility of Earth-like planets existing elsewhere in the cosmos. Written by two leading authorities on the subject, this book presents an extensive survey of the scientific problems of crustal development, and is a key reference for researchers and students in geology, geochemistry, planetary science, astrobiology and astronomy.
The goal of cancer screening is to detect disease at an early stage when treatment may be more effective. Cancer screening in dogs has relied upon annual physical examinations and routine laboratory ...tests, which are largely inadequate for detecting preclinical disease. With the introduction of non-invasive liquid biopsy cancer detection methods, the discussion is shifting from how to screen dogs for cancer to when to screen dogs for cancer. To address this question, we analyzed data from 3,452 cancer-diagnosed dogs to determine the age at which dogs of certain breeds and weights are typically diagnosed with cancer. In our study population, the median age at cancer diagnosis was 8.8 years, with males diagnosed at younger ages than females, and neutered dogs diagnosed at significantly later ages than intact dogs. Overall, weight was inversely correlated with age at cancer diagnosis, and purebred dogs were diagnosed at significantly younger ages than mixed-breed dogs. For breeds represented by ≥10 dogs, a breed-based median age at diagnosis was calculated. A weight-based linear regression model was developed to predict the median age at diagnosis for breeds represented by ≤10 dogs and for mixed-breed dogs. Our findings, combined with findings from previous studies which established a long duration of the preclinical phase of cancer development in dogs, suggest that it might be reasonable to consider annual cancer screening starting 2 years prior to the median age at cancer diagnosis for dogs of similar breed or weight. This logic would support a general recommendation to start cancer screening for all dogs at the age of 7, and as early as age 4 for breeds with a lower median age at cancer diagnosis, in order to increase the likelihood of early detection and treatment.
Water Activity and the Challenge for Life on Early Mars Tosca, Nicholas J; Knoll, Andrew H; McLennan, Scott M
Science (American Association for the Advancement of Science),
05/2008, Letnik:
320, Številka:
5880
Journal Article
Recenzirano
In situ and orbital exploration of the martian surface has shown that acidic, saline liquid water was intermittently available on ancient Mars. The habitability of these waters depends critically on ...water activity (Formula: see text), a thermodynamic measure of salinity, which, for terrestrial organisms, has sharply defined limits. Using constraints on fluid chemistry and saline mineralogy based on martian data, we calculated the maximum Formula: see text for Meridiani Planum and other environments where salts precipitated from martian brines. Our calculations indicate that the salinity of well-documented surface waters often exceeded levels tolerated by known terrestrial organisms.
Background
Prior research suggests that physicians' personal experience with breastfeeding may influence their attitudes toward breastfeeding. This phenomenon has not been explored in well‐newborn ...care physician leaders, whose administrative responsibilities often include drafting and approval of hospital breastfeeding and formula supplementation policies.
Methods
We conducted a mixed‐methods study, surveying physicians in the Better Outcomes through Research for Newborns (BORN) network. We examined physician attitudes toward recommending breastfeeding and their breastfeeding experience. Qualitative analysis was conducted on responses to the question: “How do you think your breastfeeding experience influences your clinical practice?”
Results
Of 71 participants, most (92%) had a very positive attitude toward breastfeeding with 75% of respondents reporting personal experience with breastfeeding. Of these, 68% had a very positive experience, 25% had a somewhat positive experience, and 6% had a neutral experience. Four themes emerged with respect to the effect of breastfeeding experience on practice: (1) empathy with breastfeeding struggles, (2) increased knowledge and skills, (3) passion for breastfeeding benefits, and (4) application of personal experience in lieu of evidence‐based medicine, particularly among those who struggled with breastfeeding.
Conclusions
Well‐newborn care physician leaders reported positive attitudes about breastfeeding, increased support toward breastfeeding persons, and a perception of improved clinical lactation skills. Those who struggled with breastfeeding reported increased comfort with recommending formula supplementation to their own patients. Medical education about evidence‐based breastfeeding support practices and provision of lactation support to physicians has the potential to affect public health through improved care for the patients they serve.
This qualitative study examines personal breastfeeding experiences in well‐newborn care physician leaders and how their experiences influence clinical care of breastfeeding dyads.
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