Journal articles on the topic 'Snowball Earth hypothesis'
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Ivanov, Alexei V., Anatoly M. Mazukabzov, Arkady M. Stanevich, Stanislav V. Palesskiy, and Olga A. Kozmenko. "Testing the snowball Earth hypothesis for the Ediacaran." Geology 41, no. 7 (July 2013): 787–90. http://dx.doi.org/10.1130/g34345.1.
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HARLAND, W. BRIAN. "Origins and assessment of snowball Earth hypotheses." Geological Magazine 144, no. 4 (June 6, 2007): 633–42. http://dx.doi.org/10.1017/s0016756807003391.
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Brian Harland was for many years an editor of this journal. He was also a seminal figure in the origins of the current ‘snowball Earth’ debate, having recognized in 1964 the significance of coupling emerging palaeomagnetic data on palaeolatitude with his interpretations of diamictites. Harland worked extensively in the Arctic and knew well many of the workers involved in the arguments surrounding the origin of diamictites. He thus had a unique perspective on the evidence and the disputes surrounding it. This was his last paper but he was not able to complete it before he died. However, with the help of Professor Ian Fairchild to whom we are indebted, the editors have lightly revised this work which is presented as the personal view of one of the key figures with a very broad stratigraphic appreciation of the problems of ‘snowball Earth’.Records of Precambrian glaciation onwards from the late nineteenth century led to the concept of one or more major ice ages. This concept was becoming well advanced by the mid 1930s, particularly through the compilation of Kulling in 1934. Even so tillite stratigraphy shows that glaciation was exceptional rather than typical of Earth history. Some Proterozoic tillites, sandwiched between warm marine facies, indicate low, even equatorial palaeolatitudes as determined magnetically, and more recently led to ideas of a snow- and ice-covered ‘snowball Earth’. However, interbedded non-glacial facies as well as thick tillite successions requiring abundant snowfall both militate against the hypothesis of extreme prolonged freezing temperatures referred to here as an ‘iceball Earth’ in which all oceans and seas were sealed in continuous ice cover. On the other hand tropical environments were interrupted by glaciation several times in the Proterozoic, something that did not recur in the Phanerozoic. The term ‘snowball Earth’ is consistent with the established view of extremely widespread Proterozoic glaciation, but the ‘iceball Earth’ version of this is not compatible with the geological record.
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Hoffman, Paul F., and Daniel P. Schrag. "The snowball Earth hypothesis: testing the limits of global change." Terra Nova 14, no. 3 (June 2002): 129–55. http://dx.doi.org/10.1046/j.1365-3121.2002.00408.x.
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Cooper, Barry. "‘Snowball Earth’: The Early Contribution from South Australia." Earth Sciences History 29, no. 1 (June 8, 2010): 121–45. http://dx.doi.org/10.17704/eshi.29.1.j8874825610u68w5.
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Much early discussion on the glaciations now dated as late Neoproterozoic (Cryogenian) emanated from the small geological community working in South Australia in the early twentieth century, when their age was regarded as Lower Cambrian. An initial glacial interpretation of long known ‘conglomerates’ by H. P. Woodward was made as early as 1884. Papers by Adelaide-based W. Howchin, were published in British, US and German Journals in 1908, 1911 and 1912 respectively, advocating floating sea ice as a major depositional mechanism. Sydney-based T. W. E. David was also significantly involved via the longstanding Glacial Research Committee of the Australasian Association for Advancement of Science. David publicised recognition of the glaciation at the International Geological Congress in Mexico (1906) where he also suggested that the entire earth might have been glaciated, hence foreshadowing the modern ‘snowball earth’ hypothesis. Objections to the hypothesis of a ‘Lower Cambrian’ glaciation were also raised at an early stage by Howchin's Adelaide-based colleagues. Howchin and his adversaries defended their opposing views in voluminous and fiery articles in the South Australian press in the period 1905-1912 during which both sides endeavoured to undermine their opponent's credibility. By 1907, David had also appreciated the importance of carbonate beds that succeed glacial deposition. R. Lockhart Jack recognised two major glacial episodes within the modern late Neoproterozoic as early as 1913.
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Shapiro, Russell, and Carol Dehler. "Geobiology of "Snowball Earth" deposits of Antelope Island." Geosites 1 (March 30, 2022): 1–8. http://dx.doi.org/10.31711/ugap.v1i1.100.
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Antelope Island on Great Salt Lake provides an excellent opportunity to look at one of the world’s great geobiological records—the “Snowball Earth.” Snowball Earth refers to a unique time in Earth history before the dawn of skeletonized animals where there is substantial evidence to support glaciers at sea level in the equatorial regions. Many researchers have proposed that the only way to achieve this unique condition is to freeze the entire planet, hence the “Snowball Earth” (REFS). We use quotation marks around the name of this global phenomenon because the scope and details of this major climatic phenomenon are still debated. After 30 years of rigorous testing since the idea was proposed (Kirschivink, 1992), this hypothesis is still holding up (Hoffman and others, 2017). Besides being a record of two global glaciations lasting tens of millions of years between 717 and 635 million years ago, there may be a connection between these mega-scale climate changes and the evolution of animal life.
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Tojo, Bunji, Ryo Saito, Nagayoshi Katsuta, Shin-ichi Kawakami, and Terufumi Ohno. "Neoproterozoic banded iron-formation interbedded with diamictite in Namibia and “Snowball Earth”hypothesis." Journal of the Geological Society of Japan 110, no. 6 (2004): XI—XII. http://dx.doi.org/10.5575/geosoc.110.6.xi_xii.
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Dobrzinski, Nicole, Heinrich Bahlburg, and Harald Strauss. "Geochemistry of Sinian tillites from Hunan Province, South China — A test of the Snowball Earth hypothesis *." Progress in Natural Science 13, no. 11 (November 1, 2003): 867–74. http://dx.doi.org/10.1080/10020070312331344570.
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Stern, R. J., D. Avigad, N. R. Miller, and M. Beyth. "Evidence for the Snowball Earth hypothesis in the Arabian-Nubian Shield and the East African Orogen." Journal of African Earth Sciences 44, no. 1 (January 2006): 1–20. http://dx.doi.org/10.1016/j.jafrearsci.2005.10.003.
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Campbell, Adam J., Betzalel Massarano, Edwin D. Waddington, and Stephen G. Warren. "Could promontories have restricted sea-glacier penetration into marine embayments during Snowball Earth events?" Cryosphere 11, no. 3 (May 8, 2017): 1141–48. http://dx.doi.org/10.5194/tc-11-1141-2017.
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Abstract. During the Neoproterozoic (∼ 1000–550 Ma), Earth experienced several climate excursions of extreme cold, often referred to as the Snowball Earth events. During these periods, thick flowing ice, referred to as sea glaciers, covered the entire planet's oceans. In addition, there is evidence that photosynthetic eukaryotic algae survived during these periods. With thick sea glaciers covering the oceans, it is uncertain where these organisms survived. One hypothesis is that these algae survived in marine embayments hydrologically connected to the global ocean, where the flow of sea glacier could be resisted. In order for an embayment to act as a refugium, the invading sea glacier must not completely penetrate the embayment. Recent studies have shown that straight-sided marine embayments could have prevented full sea-glacier penetration under a narrow range of climate conditions suitable for the Snowball Earth events. Here we test whether promontories, i.e., headlands emerging from a side shoreline, could further restrict sea-glacier flow. We use an ice-flow model, suitable for floating ice, to determine the flow of an invading sea glacier. We show that promontories can expand the range of climate conditions allowing refugia by resisting the flow of invading sea glaciers.
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Macouin, M., J. Besse, M. Ader, S. Gilder, Z. Yang, Z. Sun, and P. Agrinier. "Combined paleomagnetic and isotopic data from the Doushantuo carbonates, South China: implications for the “snowball Earth” hypothesis." Earth and Planetary Science Letters 224, no. 3-4 (August 2004): 387–98. http://dx.doi.org/10.1016/j.epsl.2004.05.015.
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Yang, Jun, W. Richard Peltier, and Yongyun Hu. "The Initiation of Modern “Soft Snowball” and “Hard Snowball” Climates in CCSM3. Part I: The Influences of Solar Luminosity, CO2 Concentration, and the Sea Ice/Snow Albedo Parameterization." Journal of Climate 25, no. 8 (April 10, 2012): 2711–36. http://dx.doi.org/10.1175/jcli-d-11-00189.1.
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Abstract The “Snowball Earth” hypothesis, proposed to explain the Neoproterozoic glacial episodes in the period 750–580 million years ago, suggested that the earth was globally covered by ice/snow during these events. This study addresses the problem of the forcings required for the earth to enter such a state of complete glaciation using the Community Climate System Model, version 3 (CCSM3). All of the simulations performed to address this issue employ the geography and topography of the present-day earth and are employed to explore the combination of factors consisting of total solar luminosity, CO2 concentration, and sea ice/snow albedo parameterization that would be required for such an event to occur. The analyses demonstrate that the critical conditions beyond which runaway ice–albedo feedback will lead to global freezing include 1) a 10%–10.5% reduction in solar radiation with preindustrial greenhouse gas concentrations; 2) a 6% reduction in solar radiation with 17.5 ppmv CO2; or 3) 6% less solar radiation and 286 ppmv CO2 if sea ice albedo is equal to or greater than 0.60 with a snow albedo of 0.78, or if sea ice albedo is 0.58 with a snow albedo equal to or greater than 0.80. These bifurcation points are very sensitive to the sea ice and snow albedo parameterizations. Moreover, “soft Snowball” solutions are found in which tropical open water oceans stably coexist with year-round snow-covered low-latitude continents, implying that tropical continental ice sheets would actually be present. The authors conclude that a “soft Snowball” is entirely plausible, in which the global sea ice fraction may reach as high as 76% and sea ice margins may extend to 10°S(N) latitudes.
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Ryu, Yeongjun, and Jinho Ahn. "A test for Snowball Earth hypothesis in Korean peninsula by analyzing stable carbon isotopes of carbonates from the Okcheon Supergroup." Journal of the Geological Society of Korea 52, no. 6 (December 31, 2016): 829–45. http://dx.doi.org/10.14770/jgsk.2016.52.6.829.
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Rooney, Alan D., Chuan Yang, Daniel J. Condon, Maoyan Zhu, and Francis A. Macdonald. "U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath." Geology 48, no. 6 (March 13, 2020): 625–29. http://dx.doi.org/10.1130/g47246.1.
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Abstract The snowball Earth hypothesis predicts a strong hysteresis resulting in discrete multi-million-year glaciations followed by globally synchronous deglaciation. Here we present new U-Pb zircon and Re-Os sedimentary rock geochronology and Os isotope chemostratigraphy from post-Sturtian sequences in south China to test the synchroneity of deglaciation. High-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon dates refine the minimum age of deglaciation to 660.98 ± 0.74 Ma, which is ∼2 m.y. older than previously reported. We also provide a new maximum age constraint on the onset of the Marinoan glaciation of 657.17 ± 0.78 Ma. A global compilation of new Os isotope chemostratigraphy reveals a large and systematic trend to unradiogenic values over <1 m of stratigraphy. Together, these data indicate that the Mn-carbonates in south China are not cap carbonates that formed as a response to post-snowball alkalinity, but are authigenic carbonates that formed millions of years after deglaciation. Sturtian cap carbonates tend to be absent or more condensed than their younger Marinoan counterparts. We suggest that this reflects a combination of enhanced accommodation space in early Cryogenian underfilled rift basins, stronger hysteresis, larger ice volume, and/or higher CO2 levels needed for deglaciation of the longer Sturtian glaciation. Further, our findings indicate that the apparent diachroneity of deglaciation can be explained readily as a consequence of stratigraphic condensation, itself due to the large post-Sturtian glacioeustatic transgressive sequence that outpaced shallow-water carbonate deposition.
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Hu, Y., and J. Yang. "Uncertainty of the CO<sub>2</sub> threshold for melting a hard Snowball Earth." Climate of the Past Discussions 6, no. 4 (July 12, 2010): 1337–50. http://dx.doi.org/10.5194/cpd-6-1337-2010.
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Abstract. One of the critical issues of the Snowball Earth hypothesis is how high level of CO2 is required for triggering the deglaciation. Using Community Atmospheric Model version 3 (CAM3), we study the problem for the CO2 threshold. Our simulations show large differences from previous results (Pierrehumbert, 2004, 2005). At 0.2 bars of CO2, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO2 in Le Hir et al. (2007). It is found that the diversity of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2 bar of CO2, CAM3 yields 117 Wm −2 of clear-sky greenhouse effect and 32 Wm−2 of longwave cloud forcing, versus only about 77 Wm−2 and 10.5 Wm−2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than in Pierrehumbert (2005).
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Hu, Y., J. Yang, F. Ding, and W. R. Peltier. "Model-dependence of the CO<sub>2</sub> threshold for melting the hard Snowball Earth." Climate of the Past 7, no. 1 (January 10, 2011): 17–25. http://dx.doi.org/10.5194/cp-7-17-2011.
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Abstract. One of the critical issues of the Snowball Earth hypothesis is the CO2 threshold for triggering the deglaciation. Using Community Atmospheric Model version 3.0 (CAM3), we study the problem for the CO2 threshold. Our simulations show large differences from previous results (e.g. Pierrehumbert, 2004, 2005; Le Hir et al., 2007). At 0.2 bars of CO2, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO2 in Le Hir et al. (2007). It is found that the difference of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2 bars of CO2, CAM3 yields 117 Wm−2 of clear-sky greenhouse effect and 32 Wm−2 of longwave cloud forcing, versus only about 77 Wm−2 and 10.5 Wm−2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than that in Pierrehumbert (2005). Effects of pressure broadening and collision-induced absorption are also studied using a radiative-convective model and CAM3. Both effects substantially increase surface temperature and thus lower the CO2 threshold. The radiative-convective model yields a CO2 threshold of about 0.21 bars with surface albedo of 0.663. Without considering the effects of pressure broadening and collision-induced absorption, CAM3 yields an approximate CO2 threshold of about 1.0 bar for surface albedo of about 0.6. However, the threshold is lowered to 0.38 bars as both effects are considered.
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Brocks, Jochen J. "The transition from a cyanobacterial to algal world and the emergence of animals." Emerging Topics in Life Sciences 2, no. 2 (June 29, 2018): 181–90. http://dx.doi.org/10.1042/etls20180039.
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The Neoproterozoic, 1000–541 million years (Myr) ago, saw the transition from a largely bacterial world to the emergence of multicellular grazers, suspension feeders and predators. This article explores the hypothesis that the first appearance of large, multicellular heterotrophs was fueled by an elevated supply of nutrients and carbon from the bottom of the food chain to higher trophic levels. A refined record of molecular fossils of algal sterols reveals that the transition from dominantly bacterial to eukaryotic primary production in open marine habitat occurred between 659 and 645 Myr ago, in the hot interlude between two Snowball Earth glaciations. This bacterial–eukaryotic transition reveals three characteristics: it was rapid on geological timescales, it followed an extreme environmental catastrophe and it was permanent — hallmarks of an ecological hysteresis that shifted Earth's oceans between two self-stabilizing steady states. More than 50 million years of Snowball glaciations and their hot aftermath may have purged old-world bacterial phytoplankton, providing empty but nutrient-rich ecospace for recolonization by larger algae and transforming the base of the food web. Elevated average and maximum particle sizes at the base of the food chain may have provided more efficient energy and nutrient transfer to higher trophic levels, fueling an arms race toward larger grazers, predators and prey, and the development of increasingly complex feeding and defense strategies.
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Thomson, M. R. A., and Alan P. M. Vaughan. "The role of Antarctica in the development of plate tectonic theories: from Scott to the present." Archives of Natural History 32, no. 2 (October 2005): 362–93. http://dx.doi.org/10.3366/anh.2005.32.2.362.
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One hundred years of geological research in and around Antarctica since Scott's Discovery expedition of 1901–1904 have seen the continent move from a great unknown at the margins of human knowledge to centre stage in the development of plate tectonics, continental break-up and global climate evolution. Research in Antarctica has helped make the Gondwana supercontinent a scientific fact. Discoveries offshore have provided some of the key evidence for plate tectonics and extended the evidence of global glaciation back over 30 million years. Studies of Antarctica's tectonic evolution have helped elucidate the details of continental break-up, and the continent continues to provide the best testing ground for competing scientific models. Antarctica's deep past has provided support for the “Snowball Earth” hypothesis, and for the pre-Gondwana, Rodinia supercontinent. Current research is focusing on Antarctica's subglacial lakes and basins, the possible causes of Antarctic glaciation, the evolution of its surrounding oceanic and mantle gateways, and its sub-ice geological composition and structure. None of this would have been possible without maps, and these have provided the foundation stone for Antarctic research. New mapping and scientific techniques, and new research platforms hold great promise for further major contributions from Antarctica to Earth system science in the twenty-first century.
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Zhan, Sheng, Yan Chen, Bei Xu, Bo Wang, and Michel Faure. "Late Neoproterozoic paleomagnetic results from the Sugetbrak Formation of the Aksu area, Tarim basin (NW China) and their implications to paleogeographic reconstructions and the snowball Earth hypothesis." Precambrian Research 154, no. 3-4 (April 2007): 143–58. http://dx.doi.org/10.1016/j.precamres.2007.01.001.
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Guerroué, Erwan Le, Philip Allen, and Andrea Cozzi. "Two distinct glacial successions in the Neoproterozoic of Oman." GeoArabia 10, no. 2 (April 1, 2005): 17–34. http://dx.doi.org/10.2113/geoarabia100217.
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ABSTRACT Neoproterozoic glacial strata in Oman are key to the ongoing Snowball Earth discussion, providing a great opportunity to test the hypothesis. The Abu Mahara Group (Huqf Supergroup) is well exposed in the core of the Jabal Akhdar of northern Oman. It contains two glaciogenic units, the Ghubrah Formation (723+16/−10 Ma) and the Fiq Formation (currently undated), that are separated by the volcaniclastic Saqlah Formation. An angular unconformity is present between the Ghubrah and Saqlah formations, indicating a significant time gap between the deposition of the Ghubrah and Fiq glacial successions. The localised occurrence of pillow basalts and more widespread volcaniclastics of the Saqlah Formation, suggests the initiation of a rifting phase, which is considered to have continued during deposition of the Fiq Formation. Given the available geochronology, the Ghubrah Formation may correlate with other glaciogenic successions worldwide attributed to the Sturtian glacial epoch, and the Fiq Formation with younger glaciogenic successions attributed to the Marinoan glacial epoch. Neoproterozoic glaciations appear to have taken place at times of tectonically generated accommodation, suggesting a link between geodynamics, basin development and climate change.
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Domack, E. W., and P. F. Hoffman. "An ice grounding-line wedge from the Ghaub glaciation (635 Ma) on the distal foreslope of the Otavi carbonate platform, Namibia, and its bearing on the snowball Earth hypothesis." Geological Society of America Bulletin 123, no. 7-8 (January 26, 2011): 1448–77. http://dx.doi.org/10.1130/b30217.1.
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Mirmoadi, Bagaskara Sih, and Yohana Wuri Satwika. "Hubungan Antara Literasi Digital Dengan Self Regulated Learning Pada Mahasiswa." JDMP (Jurnal Dinamika Manajemen Pendidikan) 7, no. 1 (October 23, 2022): 8–23. http://dx.doi.org/10.26740/jdmp.v7n1.p8-23.
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Problems that arise during the online learning period continue to increase over time, which is about self-regulated learning. The purpose of this study was to determine the relationship between digital literacy and self-regulated learning in students. The research sample amounted to 248 based on the snowball sampling technique, which were Unesa students registered on the PDDikti page. The data analysis is in the form of assumption test using normality test and linearity test and hypothesis testing using simple correlation. Based on the results, there was a significant relationship between digital literacy and self-regulated learning which was positive, but relatively low. This is based on the Pearson correlation value of 0.315 and the sig. 0.00. Increased digital literacy makes self-regulated learning also increase. Another result of this study is that digital literacy provides an effective contribution to the explanation of self-regulated learning by 9.9%, while the remaining 90.1% can be explained by other factors not examined in this study. Key words: digital literacy, self regulated learning, students, online learning Abstrak: Permasalahan yang muncul selama masa pembelajaran daring terus bertambah seiring berjalannya waktu, salah satunya mengenai self regulated learning. Tujuan dari penelitian ini untuk mengetahui hubungan antara literasi digital dengan self regulated learning pada mahasiswa dengan metode kuantitatif korelasional. Sampel penelitian berjumlah 248 berdasarkan teknik sampling snowball yang merupakan mahasiswa Unesa yang terdaftar dalam laman PDDikti. Analisa data penelitian ini berupa uji asumsi menggunakan uji normalitas dan uji linearitas serta uji hipotesis menggunakan korelasi sederhana. Berdasarkan hasil penelitian diperoleh hubungan signifikan antara literasi digital dan self regulated learning yang positif, namun tergolong rendah. Hal ini didasarkan pada nilai pearson correlation sebesar 0, 315 dan nilai sig. 0,00. Literasi digital yang meningkat menjadikan self regulated learning meningkat pula. Hasil lain dari penelitian ini yaitu literasi digital memberikan sumbangan efektif pada penjelasan self regulated learning sebesar 9,9%, sedangkan sisanya 90,1% dapat dijelaskan oleh faktor lain yang tidak diteliti dalam penelitian ini. Kata kunci: literasi digital, self regulated learning, mahasiswa, pembelajaran daring
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Saragih, Andre Kalpin, and Rapina Rapina. "The Effect of Emotional Intelligence on Audit Quality." International Journal of Entrepreneurship, Business and Creative Economy 2, no. 2 (July 30, 2022): 57–69. http://dx.doi.org/10.31098/ijebce.v2i2.989.
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Background - The implementation of Community Activity Restrictions or PPKM is one of the efforts to prevent the spread of the Coronavirus. This makes independent auditors have to be able to complete their duties even though they are working from home. Objectives - This study has the objective to examine and test whether or not there is an influence of the independent variable (emotional intelligence) on the dependent or dependent variable (audit quality). Design/Methodology - This study uses primary data by distributing questionnaires using the snowball sampling method. The populations of this study are auditors who work in public accounting firms in Jakarta and Bandung, while the sample in this study is 44 auditors in public accounting firms in Jakarta and Bandung. Hypothesis testing using simple linear analysis with SPSS Version 26. Findings - This study found that emotional intelligence has an effect on audit quality; namely, when emotional intelligence increases, audit quality also increases. The emotional intelligence of the auditor is able to influence the quality of the audit seen by the auditors who work in public accounting firms. Research Limitations - Furthermore, one of the problems in this study is the limited time in distributing questionnaires; the researchers only took samples in the cities of Jakarta and Bandung. Originality/Value - This research was conducted to convey information as well as input for the development of knowledge in the field of auditing in Indonesia, especially in improving audit quality, and to provide empirical evidence on the effect of emotional intelligence on audit quality.
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Voigt, A., and D. S. Abbot. "Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins." Climate of the Past Discussions 8, no. 4 (July 3, 2012): 2445–75. http://dx.doi.org/10.5194/cpd-8-2445-2012.
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Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare sea ice albedo is assumed because bare sea ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics have a much larger influence on the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude sea-ice margins. Our results indicate that differences in sea-ice dynamics schemes can be as important as sea ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.
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Voigt, A., and D. S. Abbot. "Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins." Climate of the Past 8, no. 6 (December 21, 2012): 2079–92. http://dx.doi.org/10.5194/cp-8-2079-2012.
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Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO2, SI)* in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma) continents and solar insolation (94% of modern). In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Replacing the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true Jormungand state. Overall, our results demonstrate that differences in sea-ice dynamics schemes can be at least as important as differences in sea-ice albedo for causing the spread in climate models' estimates of the Snowball Earth bifurcation. A detailed understanding of Snowball Earth initiation therefore requires future research on sea-ice dynamics to determine which model's simulation is most realistic.
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George, Apostolou, Papatsimpas Achilleas, Gounas Athanasios, and Gkouna Ourania. "Distance Learning in Greece during Covid-19 Pandemic." Global Research in Higher Education 4, no. 2 (June 3, 2021): p69. http://dx.doi.org/10.22158/grhe.v4n2p69.
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The purpose of this study is to investigate the reaction of Greeks to this new educational reality due to the Covid-19 outbreak. Since the first restrictive measures were implemented in March 2020in Greece, distance learning has become a dynamic part of people’s daily lives with the prospect of remain in gas such in the future. A total of N=170 students, parents, teachers, civil servants, private sector employees who were involved in the distance learning process either as instructors or as students in the period of Covid-19 pandemic in Greece, were selected with the use of snowball sampling. A questionnaire using demographic and satisfaction related variables was completed by the respondents, namely citizens across Greece, based on a Likert scale questionnaire which is a useful and multidimensional instrument, to assess satisfaction within the time frame from July 7, 2020 to October 20, 2020; the period when there occurred a loosening in the restrictive measures between the two lockdowns in Greece. It was investigated how the demographic factors, specifically gender, age, occupation, and place of residence, influence the attitude of the respondents towards synchronous and asynchronous distance learning as well as their intention to continue using online education services in the future after the lifting of the restrictive measures. Additionally, the customers’ preferences concerning the most enjoyable distance learning experience were examined, so that they will be available to the distance learning program designers. Descriptive statistical analysis and non-parametric statistical hypothesis tests were conducted in SPSS and R. Most of the respondents had not participated in online courses before the Covid-19 outbreak, 46 % did participate in e-learning courses before the Covid-19 lockdown while 54 % did not and 34.1% respondents prefer face-to-face learning, while 15.9% prefer e-learning. Also, 50% respondents prefer a combination of face-to-face learning and e-learning. Hypothesis tests showed that there are statistically significant differences between users’ preferences as well as regarding their demographic characteristics. Undergraduate and postgraduate university students continue to participate in online learning courses and are willing to invest financial resources and time in this new educational process (?2(4)=10.440, p=0.034), unlike high school students who prefer face-to-face learning (p=0.042). The present study will lead to practical implications, such as the formation of e-learning programs which aim for the best user experience and the best learning outcomes. Also, private educational organizations can include the results in the key elements to implementing a strategic marketing mix.
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Harman, C. E., Ravi Kumar Kopparapu, Guðmundur Stefánsson, Andrea S. J. Lin, Suvrath Mahadevan, Christina Hedges, and Natasha E. Batalha. "A Snowball in Hell: The Potential Steam Atmosphere of TOI-1266c." Planetary Science Journal 3, no. 2 (February 1, 2022): 45. http://dx.doi.org/10.3847/psj/ac38ac.
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Abstract TOI-1266c is a recently discovered super-Venus in the radius valley orbiting an early M dwarf. However, its notional bulk density (∼2.2 g cm−3) is consistent with a large volatile fraction, suggesting that it might have volatile reservoirs that have survived billions of years at more than twice Earth’s insolation. On the other hand, the upper mass limit paints a picture of a cool super-Mercury dominated by >50% iron core (∼9.2 g cm−3) that has tiptoed up to the collisional stripping limit and into the radius gap. Here we examine several hypothetical states for TOI-1266c using a combination of new and updated open-source atmospheric escape, radiative−convective, and photochemical models. We find that water-rich atmospheres with trace amounts of H2 and CO2 are potentially detectable (S/N > ∼ 5) in less than 20 hr of James Webb Space Telescope (JWST) observing time. We also find that water vapor spectral features are not substantially impacted by the presence of high-altitude water or ice clouds owing to the presence of a significant amount of water above the cloud deck, although further work with self-consistent cloud models is needed. Regardless of its mass, however, TOI-1266c represents a unique proving ground for several hypotheses related to the evolution of sub-Neptunes and Venus-like worlds, particularly those near the radius valley.
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Halverson, Galen P., Susannah M. Porter, and Timothy M. Gibson. "Dating the late Proterozoic stratigraphic record." Emerging Topics in Life Sciences 2, no. 2 (July 13, 2018): 137–47. http://dx.doi.org/10.1042/etls20170167.
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The Tonian and Cryogenian periods (ca. 1000–635.5 Ma) witnessed important biological and climatic events, including diversification of eukaryotes, the rise of algae as primary producers, the origin of Metazoa, and a pair of Snowball Earth glaciations. The Tonian and Cryogenian will also be the next periods in the geological time scale to be formally defined. Time-calibrating this interval is essential for properly ordering and interpreting these events and establishing and testing hypotheses for paleoenvironmental change. Here, we briefly review the methods by which the Proterozoic time scale is dated and provide an up-to-date compilation of age constraints on key fossil first and last appearances, geological events, and horizons during the Tonian and Cryogenian periods. We also develop a new age model for a ca. 819–740 Ma composite section in Svalbard, which is unusually complete and contains a rich Tonian fossil archive. This model provides useful preliminary age estimates for the Tonian succession in Svalbard and distinct carbon isotope anomalies that can be globally correlated and used as an indirect dating tool.
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Owusu, Dinah Rachael. "THE EFFECT OF TRUST, ACCESSIBILITY OF SERVICES AND STIGMATIZATION ON THE PATRONAGE OF GUIDANCE AND COUNSELING SERVICES BY STUDENTS IN PUBLIC UNIVERSITIES IN KUMASI METROPOLIS/ASHANTI REGION." Education Sustainability & Society 5, no. 2 (2022): 71–75. http://dx.doi.org/10.26480/ess.02.2022.71.75.
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Students need guidance in environment and health linkages, plus gaining attitudes, info, and skills that result in failure or success of life. Counseling is progressively vital to encourage well-being of a child. Effective advice and counseling must aid students improve their self-esteem and attain their life goals. It is critical to emphasize that thorough advice and counseling is one strategy to achieve educational greatness. Guidance and counselling services are widely recognized as being beneficial in molding the making of decision and pupils’ and employees’ thinking abilities. The study involved students at universities in the Kumasi metropolis in examining the effect of trust, accessibility of services and stigmatization on guidance and counseling services’ patronage. The study employed quantitative research with survey design. This study method was considered as explanatory to test the hypotheses. The population of the study was 3577 students at Kumasi Technical University and Akenten Appiah-Menka University of Skills Training and Entrepreneural Development. The researcher employed a non-probability sampling which is a snowball sampling technique. The sample size was determined by the number of responses obtained which was 236. The researcher employed Google Forms to collect data. The quantitative tools used were Statistical Package for Social Sciences (SPSS 26) and Microsoft Excel to analyze data. The study revealed that trust was positively and significantly related with counseling and guidance services’ patronage by tertiary students. The study found that accessibility of services was positively and significantly related with counseling and guidance services’ patronage by tertiary students. The study further revealed that stigmatization was positively and significantly related with counseling and guidance services’ patronage by tertiary students.
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Mitchell, Ross N., Thomas M. Gernon, Grant M. Cox, Adam R. Nordsvan, Uwe Kirscher, Chuang Xuan, Yebo Liu, Xu Liu, and Xiaofang He. "Orbital forcing of ice sheets during snowball Earth." Nature Communications 12, no. 1 (July 7, 2021). http://dx.doi.org/10.1038/s41467-021-24439-4.
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AbstractThe snowball Earth hypothesis—that a runaway ice-albedo feedback can cause global glaciation—seeks to explain low-latitude glacial deposits, as well as geological anomalies including the re-emergence of banded iron formation and “cap” carbonates. One of the most significant challenges to snowball Earth has been sedimentological cyclicity that has been taken to imply more climate dynamics than expected when the ocean is completely covered in ice. However, recent climate models suggest that as atmospheric CO2 accumulates, the snowball climate system becomes sensitive to orbital forcing. Here we show the presence of nearly all Milankovitch (orbital) cycles preserved in stratified banded iron formation deposited during the Sturtian snowball Earth. These results provide evidence for orbitally forced cyclicity of global ice sheets that resulted in periodic oxidation of ferrous iron. Orbital glacial advance and retreat cycles provide a simple mechanism to reconcile both the sedimentary dynamics and the enigmatic survival of multicellular life during snowball Earth.
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de Vrese, Philipp, Tobias Stacke, Jeremy Caves Rugenstein, Jason Goodman, and Victor Brovkin. "Snowfall-albedo feedbacks could have led to deglaciation of snowball Earth starting from mid-latitudes." Communications Earth & Environment 2, no. 1 (May 14, 2021). http://dx.doi.org/10.1038/s43247-021-00160-4.
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AbstractSimple and complex climate models suggest a hard snowball – a completely ice-covered planet – is one of the steady-states of Earth’s climate. However, a seemingly insurmountable challenge to the hard-snowball hypothesis lies in the difficulty in explaining how the planet could have exited the glaciated state within a realistic range of atmospheric carbon dioxide concentrations. Here, we use simulations with the Earth system model MPI-ESM to demonstrate that terminal deglaciation could have been triggered by high dust deposition fluxes. In these simulations, deglaciation is not initiated in the tropics, where a strong hydrological cycle constantly regenerates fresh snow at the surface, which limits the dust accumulation and snow aging, resulting in a high surface albedo. Instead, comparatively low precipitation rates in the mid-latitudes in combination with high maximum temperatures facilitate lower albedos and snow dynamics that – for extreme dust fluxes – trigger deglaciation even at present-day carbon dioxide levels.
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Lan, Zhongwu, Shitou Wu, Nick M. W. Roberts, Shujing Zhang, Rong Cao, Hao Wang, and Yueheng Yang. "Geochronological and geochemical constraints on the origin of highly 13Ccarb-depleted calcite in basal Ediacaran cap carbonate." Geological Magazine, April 4, 2022, 1–12. http://dx.doi.org/10.1017/s001675682200019x.
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Abstract Ediacaran cap dolostone atop Marinoan glacial deposits contains complex sedimentary structures with extremely negative δ13Ccarb values in close association with oscillations in palaeoclimatic and oceanographic proxy records. However, the precise geological, geochronological and geochemical context of the cap dolostone is not clarified, which hampers us from correctly interpreting the extremely negative δ13Ccarb values and their causal relationships with the Snowball Earth hypothesis. In this study, we conducted detailed in situ geochronological and geochemical analyses on the calcite within the cap dolostone from the Ediacaran Doushantuo Formation in South China in order to define its formation and relationship to the Snowball Earth hypothesis. Petrographic observations show that formation of dolomite pre-dates precipitation of calcite and pyrite, which pre-dates quartz cementation in the basal cap carbonate. Calcite cement within the cap dolostone yielded a U–Pb age of 636.5 ± 7.4/17.8 Ma (2σ, MSWD = 1.6, n = 36/40), which is within uncertainty of a published dolomite U–Pb age of 632 ± 17 Ma (recalculated as 629.3 ± 16.7/22.9 Ma). These age constraints negate the possibility that the calcite cement was formed by late Ediacaran or Cambrian hydrothermal activity. The rare earth element distribution patterns suggest a dominant seawater origin overprinted by subsequent early Ediacaran hydrothermal activity. The combined age, petrographic and geochemical data suggest oxidization of methane clathrates in response to complicated interplay between eustasy and isostatic rebound and hydrothermal fluids.
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McDannell, Kalin T., and C. Brenhin Keller. "Cryogenian glacial erosion of the central Canadian Shield: The “late” Great Unconformity on thin ice." Geology, September 5, 2022. http://dx.doi.org/10.1130/g50315.1.
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The Great Unconformity has been recognized for more than a century, but only recently have its origins become a subject of debate. Hypotheses suggest global Snowball Earth glaciations and tectonic processes associated with the supercontinent Rodinia as drivers of widespread kilometer-scale erosion in the late Neoproterozoic. We present new integrated zircon and apatite (U-Th)/He and fission-track thermochronology from Precambrian basement samples of the central Canadian Shield in northern Manitoba to test these ideas. Bayesian inverse modeling indicates that 150–200 °C of cooling (>3 km of exhumation) occurred simultaneously with Cryogenian glaciations at ca. 690–650 Ma within interior North America. This estimate for the timing of unroofing is more precise than previous appraisals and does not align with any known tectonic or magmatic events (i.e., large igneous province eruptions) potentially associated with the supercontinent cycle that occurred during the late Proterozoic along the Laurentian margins. Based on these results and interpretations, the timing and magnitude of exhumation is best explained by glacial erosion, and further establishes the importance of multiple thermochronometers for resolving detailed deeptime thermal histories.