A primordial atmospheric origin of hydrospheric deuterium enrichment on Mars

The deuterium-to-hydrogen (D/H or 2H/1H) ratio of Martian atmospheric water (~6x standard mean ocean water, SMOW) is higher than that of known sources, requiring planetary enrichment. A recent measurement by NASA's Mars Science Laboratory rover Curiosity of >3 Gyr clays yields a D/H ratio ~3x SMOW, demonstrating that most enrichment occurs early in Mars's history. As on Venus, Mars's D/H enrichment is thought to reflect preferential loss to space of 1H (protium) relative to 2H (deuterium), but the global environmental context of large and early hydrogen losses remain to be determined. Here, we apply a recent model of primordial atmosphere evolution to Mars, link the magma ocean of the accretion epoch with a subsequent water-ocean epoch, and calculate the behavior of deuterium for comparison with the observed record. We find that a ~2-3x hydrospheric deuterium-enrichment is produced if the Martian magma ocean is chemically reducing at last equilibration with the primordial atmosphere, making H2-CO the initially dominant species, with minor abundances of H2O-CO2. Reducing gases - in particular H2 - can cause greenhouse warming and prevent a water ocean from freezing immediately after the magma ocean epoch. Moreover, the pressure-temperature conditions are high enough to produce ocean-atmosphere H2O-H2 isotopic equilibrium such that surface H2O strongly concentrates deuterium relative to H2, which preferentially takes up protium and escapes from the primordial atmosphere. The proposed scenario of primordial H2-rich outgassing and escape suggests significant durations (>Myr) of chemical conditions on the Martian surface conducive to prebiotic chemistry immediately following Martian accretion.Comment: 5 figure

A psychometric lens for e-learning: Examining the validity and reliability of the persian version of University Students’ Engagement Inventory (P-USEI)

Student engagement is a critical component of e-learning, which became an important focus for most academic institutions during the COVID-19 pandemic. University students’ engagement is measured using various scales with diferent subscales. This study aimed to evaluate the psychometric properties of the Persian version of the University Student Engagement Inventory (P-USEI). A cross-sectional methodology study was conducted among Iranian university students (n =667) from April to May 2020. After forward–backward translation, the content, and construct validity, and reliability of the scale were assessed. The results obtained from the confrmatory factor analysis confrmed that the P-USEI has three factors: cognitive, emotional, and behaviour. The fndings of the study supported the adequate reliability, factorial, convergent, and discriminant validities of P-USEI in a sample of Iranian students. The P-USEI dimensions have predictive value for important academic variables that can be generalized by developing the research through a psychometric evaluation on student engagement.info:eu-repo/semantics/publishedVersio

Student satisfaction and academic efficacy during online learning with the mediating effect of student engagement: A multi-country study.

The COVID-19 pandemic caused unprecedented changes to educational institutions, forcing their closure and a subsequent shift to online education to cater to student learning requirements. However, successful online learning depends on several factors and may also vary between countries. As such, this cross-sectional study sought to investigate how engagement of university students, a major driver of online learning, was influenced by course content, online interaction, student acceptance, and satisfaction with online learning, as well as self-efficacy across nine countries (China, India, Iran, Italy, Malaysia, Portugal, Serbia, Turkey, and the United Arab Emirates) during the COVID-19 pandemic. Using a questionnaire-based approach, data collected from 6,489 university students showed that student engagement was strongly linked to perception of the quality of the course content and online interactions (p < .001). The current study also indicated that online interactions are a major determinant of academic efficacy but only if mediated by engagement within the online learning context. A negative correlation between student engagement and satisfaction with online learning was found, demonstrating the importance of students being engaged behaviorally, emotionally, and cognitively to feel satisfied with learning. Academic efficacy and student satisfaction were explained by course content, online interaction, and online learning acceptance, being mediated by student engagement. Student satisfaction and, to a lesser degree academic efficacy, were also associated with online learning acceptance. Overall, the structural equation model was a good fit for the data collected from all nine countries (CFI = .947, TLI = .943; RMSEA = .068; SRMR = .048), despite differences in the percentage variations explained by each factor (no invariance), likely due to differences in levels of technology use, learning management systems, and the preparedness of teachers to migrate to full online instruction. Despite limitations, the results of this study highlight the most important factors affecting online learning, providing insight into potential approaches for improving student experiences in online learning environments

Equilibration in the Aftermath of the Lunar-Forming Giant Impact

Simulations of the moon-forming impact suggest that most of the lunar material derives from the impactor rather than the Earth. Measurements of lunar samples, however, reveal an oxygen isotope composition that is indistinguishable from terrestrial samples, and clearly distinct from meteorites coming from Mars and Vesta. Here we explore the possibility that the silicate Earth and impactor were compositionally distinct with respect to oxygen isotopes, and that the terrestrial magma ocean and lunar-forming material underwent turbulent mixing and equilibration in the energetic aftermath of the giant impact. This mixing may arise in the molten disk epoch between the impact and lunar accretion, lasting perhaps 10^2-10^3 yr. The implications of this idea for the geochemistry of the Moon, the origin of water on Earth, and constraints on the giant impact are discussed.Comment: 34 pages, 5 figure

CHEMICAL AND ISOTOPIC CONSEQUENCES OF LUNAR FORMATION VIA GIANT IMPACT

“We must trust the perfection of the creation so far, as to believe that whatever curiosity the order of things has awakened in our minds, the order of things can satisfy.” – Ralph Waldo Emerson, NatureACKNOWLEDGEMENTS iv This thesis would not have been possible without the help and support of many people. First and foremost, I would like to thank my parents for coming to the United States after living through a revolution and a war, and for starting a new life in a foreign country so that their children might have a better future. Maman and Baba: az tah-e delam, merci. I would like to thank my thesis advisor, Dave Stevenson, for providing uncompromising guidance and support and for giving me the freedom to pursue ideas that at first glance appear crazy. The central idea explored in this thesis is his. Dave’s willingness to challenge seemingly established ideas, his scientific breadth and depth, and his wisdom and humor have been an enormous inspiration. I am thankful to Paul Asimow for lending his uncommon expertise in thermodynamics and to John Eiler whose casual questions during planetary science seminar resulted in Chapter 4 of this thesis. I owe a debt of gratitude to Alessandro Morbidelli wh

Chemical and Isotopic Consequences of Lunar Formation via Giant Impact

There is near consensus in the planetary science community that the origin of the Moon can be traced to a massive interplanetary collision between a roughly Mars-sized object and the growing Earth towards the end of planetary accretion. Many in the geochemical community, however, have rightly expressed skepticism towards this hypothesis. The compositional signatures of the giant impact have never been clearly articulated, and no one has yet used the ideas of lunar origin to say something about the lunar composition that was not previously known, that is, to make a prediction. The work presented here seeks to develop the theory of lunar origin with two goals in mind: of reconciling the predictions of the dynamical scenario with the observed signatures in the lunar composition, and of making new predictions for the lunar chemical and isotopic composition that can test and further constrain the theory through comparison with observations

Hydrogen isotopic evidence for early oxidation of silicate Earth

The Moon-forming giant impact extensively melts and partially vaporizes the silicate Earth and delivers a substantial mass of metal to Earth's core. Subsequent evolution of the magma ocean and overlying atmosphere has been described by theoretical models but observable constraints on this epoch have proved elusive. Here, we report calculations of the primordial atmosphere during the magma ocean and water ocean epochs and forge new links with observations to gain insight into the behavior of volatiles on the early Earth. As Earth's magma ocean crystallizes, it outgasses the bulk of the volatiles into the primordial atmosphere. The redox state of the magma ocean controls both the chemical composition of the outgassed volatiles and the hydrogen isotopic composition of water oceans that remain after hydrogen loss from the primordial atmosphere. Whereas water condenses and is retained, molecular hydrogen does not condense and can escape, allowing large quantities (~10^2 bars) of hydrogen - if present - to be lost from Earth in this epoch. Because the escaping inventory of H can be comparable to the hydrogen inventory in the early oceans, the corresponding deuterium enrichment can be large with a magnitude that depends on the initial H2 inventory. By contrast, the common view that terrestrial water has a carbonaceous chondrite source requires the oceans to preserve the isotopic composition of that source, undergoing minimal D-enrichment via H2 loss. Such minimal enrichment places upper limits on the amount of primordial H2 in contact with early water oceans (pH2&lt;20 bars), implies oxidizing conditions for outgassing from the magma ocean, and suggests that Earth's mantle supplied the oxidant for the chemical resorption of metals during late accretion