@article{johanesen_claiborne_falk_hubbard_kohfeld_nadin_schmidt_2023, title={Common-sense teaching for the 2020s: Ungrading in response to covid-19 and beyond}, url={http://dx.doi.org/10.1080/10899995.2023.2259784}, DOI={10.1080/10899995.2023.2259784}, abstractNote={Conventional letter- or number-based grading systems, though ubiquitous at all levels of education, do not optimize the learning experience. The philosophy of “ungrading” includes a variety of approaches that decenter or even remove numeric or letter scoring of student work in favor of descriptive feedback, opportunities for revision, self-assessment and reflection, and assessment toward mastery. This paper presents one of the few published descriptions of the use of ungrading approaches in geoscience courses at the undergraduate and graduate level. We showcase four approaches, detailing the courses and ungrading structures used, positive outcomes and challenges, and tools that might allow others to apply these methods. We describe (a) mastery and specifications grading, chosen to promote mastery of course materials in mid- and upper-level courses for college majors; (b) labor-based grading used to promote depth of student learning by focusing on revision; (c) collaborative grading utilizing self-assessment and reflection chosen to promote meta-cognition and growth mindset; and, (d) partial ungrading as a means to begin the ungrading process. Importantly, our experiences have led us to recognize the equity that ungrading approaches create, enabling students from different backgrounds, including students of color and disabled students, to find stronger support and build greater competence and confidence in geoscience classes.}, journal={Journal of Geoscience Education}, author={Johanesen, Katharine E. and Claiborne, Lily L. and Falk, Elisabeth S. and Hubbard, Karla Parsons and Kohfeld, Karen E. and Nadin, Elisabeth S. and Schmidt, Amanda H.}, year={2023}, month={Sep} }
 @article{falk_guo_paukert_matter_mervine_kelemen_2016, title={Controls on the stable isotope compositions of travertine from hyperalkaline springs in Oman: Insights from clumped isotope measurements}, url={http://dx.doi.org/10.1016/j.gca.2016.06.026}, DOI={10.1016/j.gca.2016.06.026}, abstractNote={Carbonate formation at hyperalkaline springs is typical of serpentinization in peridotite massifs worldwide. These travertines have long been known to exhibit large variations in their carbon and oxygen isotope compositions, extending from apparent equilibrium values to highly depleted values. However, the exact causes of these variations are not well constrained. We analyzed a suite of well-characterized fresh carbonate precipitates and travertines associated with hyperalkaline springs in the peridotite section of the Samail ophiolite, Sultanate of Oman, and found their clumped isotope compositions vary systematically with formation environments. Based on these findings, we identified four main processes controlling the stable isotope compositions of these carbonates. These include hydroxylation of CO2, partial isotope equilibration of dissolved inorganic carbon, mixing between isotopically distinct carbonate end-members, and post-depositional recrystallization. Most notably, in fresh crystalline films on the surface of hyperalkaline springs and in some fresh carbonate precipitates from the bottom of hyperalkaline pools, we observed large enrichments in Δ47 (up to ∼0.2‰ above expected equilibrium values) which accompany depletions in δ18O and δ13C, yielding about 0.01‰ increase in Δ47 and 1.1‰ decrease in δ13C for every 1‰ decrease in δ18O, relative to expected equilibrium values. This disequilibrium trend, also reflected in preserved travertines ranging in age from modern to ∼40,000 years old, is interpreted to arise mainly from the isotope effects associated with the hydroxylation of CO2 in high-pH fluids and agrees with our first-order theoretical estimation. In addition, in some fresh carbonate precipitates from the bottom of hyperalkaline pools and in subsamples of one preserved travertine terrace, we observed additional enrichments in Δ47 at intermediate δ13C and δ18O, consistent with mixing between isotopically distinct carbonate end-members. Our results suggest that carbonate clumped isotope analysis can be a valuable tool for identifying and distinguishing processes not readily apparent from the carbonate bulk stable isotope compositions alone, e.g., kinetic effects or mixing of different carbonate end-members, which can significantly alter both the apparent formation temperatures and apparent radiocarbon ages. The isotope trends observed in these travertine samples could be applied more broadly to identify extinct hyperalkaline springs in terrestrial and extraterrestrial environments, to better constrain the formation conditions and post-depositional alteration of hyperalkaline spring carbonates, and to extract potential paleoclimate information.}, journal={Geochimica et Cosmochimica Acta}, author={Falk, E.S. and Guo, W. and Paukert, A.N. and Matter, J.M. and Mervine, E.M. and Kelemen, P.B.}, year={2016}, month={Nov} }
 @article{falk_kelemen_2015, title={Geochemistry and petrology of listvenite in the Samail ophiolite, Sultanate of Oman: Complete carbonation of peridotite during ophiolite emplacement}, volume={160}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84927725756&partnerID=MN8TOARS}, DOI={10.1016/j.gca.2015.03.014}, abstractNote={Extensive outcrops of listvenite—fully carbonated peridotite, with all Mg in carbonate minerals and all Si in quartz—occur along the basal thrust of the Samail ophiolite in Oman. These rocks can provide insight into processes including (a) carbon fluxes at the “leading edge of the mantle wedge” in subduction zones and (b) enhanced mineral carbonation of peridotite as a means of carbon storage. Here we examine mineralogical, chemical and isotopic evidence on the temperatures, timing, and fluid compositions involved in the formation of this listvenite. The listvenites are composed primarily of magnesite and/or dolomite + quartz + relict Cr-spinel. In some instances the conversion of peridotite to listvenite is nearly isochemical except for the addition of CO2, while other samples have also seen significant calcium addition and/or variable, minor addition of K and Mn. Along margins where listvenite bodies are in contact with serpentinized peridotite, talc and antigorite are present in addition to carbonate and quartz. The presence of antigorite + quartz + talc in these samples implies temperatures of 80–130 °C. This range of temperature is consistent with dolomite and magnesite clumped isotope thermometry in listvenite (average T = 90 ± 15 °C) and with conventional mineral-water oxygen isotope exchange thermometry (assuming fluid δ18O near zero). CO2-bearing fluids responsible for the formation of listvenite were likely derived from underlying calcite-bearing metasediment during emplacement of the ophiolite. An internal Rb–Sr isochron from one listvenite sample yields an age of 97 ± 29 Ma, consistent with the timing of emplacement of the ophiolite over allochthonous sediments of the Hawasina group, and autochthonous sediments of the Arabian continental margin. Most of the initial 87Sr/86Sr values in the listvenite, ranging from 0.7085 to 0.7135, are significantly higher than seawater values and consistent with values measured in the underlying metasediments. While constraints on the pressure of listvenite formation are lacking, the moderate temperatures suggest that listvenites formed at relatively shallow depths in the subduction zone, making release of carbonate-saturated pore-water due to compaction of subducted sediment or low-pressure phase transitions of hydrous minerals, such as clays, probable sources of the CO2-bearing fluid. Carbonate dissolution from subducted sediments and transfer of CO2 to the mantle wedge to form listvenites may be an important process in forearc hydrothermal systems. Additionally, the presence of listvenites demonstrate that peridotite carbonation reactions can proceed to completion on large scales, suggesting that in situ mineral carbonation of peridotite may offer a viable solution for carbon storage.}, journal={Geochimica et Cosmochimica Acta}, author={Falk, E.S. and Kelemen, P.B.}, year={2015}, pages={70–90} }
 @article{streit_kelemen_eiler_2012, title={Coexisting serpentine and quartz from carbonate-bearing serpentinized peridotite in the Samail Ophiolite, Oman}, volume={164}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84867582769&partnerID=MN8TOARS}, DOI={10.1007/s00410-012-0775-z}, abstractNote={Tectonically exposed mantle peridotite in the Oman Ophiolite is variably serpentinized and carbonated. Networks of young carbonate veins are prevalent in highly serpentinized peridotite, particularly near low-temperature alkaline springs emanating from the peridotite. An unusual feature in some samples is the coexistence of serpentine and quartz, which is not commonly observed in serpentinites. This assemblage is unstable with respect to serpentine + talc or talc + quartz under most conditions. Serpentine in the carbonated serpentinites in this study is more iron rich than in most serpentinites reported in previous studies, and samples with co-existing quartz contain the most iron-rich serpentines. Calculations of thermodynamic equilibria in the MgO–SiO2–H2O–CO2 system suggest that serpentine + quartz may be a stable assemblage at low temperatures (e.g., <~15–50 °C) and is stabilized to higher temperatures by preferential cation substitutions in serpentine over talc. Based on these calculations, serpentine + quartz assemblages could result from serpentinization at near-surface temperatures. Clumped isotope thermometry of carbonate veins yields temperatures within error of the observed temperatures in Oman groundwater for all samples analyzed, while the δ18O of water calculated to be in equilibrium with carbonate precipitated at those temperatures is within error of the observed isotopic composition of Oman groundwater for the majority of samples analyzed. As groundwater geochemistry suggests that carbonate precipitation and serpentinization occur concomitantly, this indicates that both hydration and carbonation of peridotite are able to produce extensive alteration at the relatively low temperatures of the near-surface weathering environment.}, number={5}, journal={Contributions to Mineralogy and Petrology}, author={Streit, E. and Kelemen, P. and Eiler, J.}, year={2012}, pages={821–837} }
 @book{kelemen_matter_streit_rudge_curry_blusztajn_2011, title={Rates and mechanisms of mineral carbonation in peridotite: Natural processes and recipes for enhanced, in situ CO2 capture and storage}, volume={39}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79955148489&partnerID=MN8TOARS}, DOI={10.1146/annurev-earth-092010-152509}, abstractNote={ Near-surface reaction of CO2-bearing fluids with silicate minerals in peridotite and basalt forms solid carbonate minerals. Such processes form abundant veins and travertine deposits, particularly in association with tectonically exposed mantle peridotite. This is important in the global carbon cycle, in weathering, and in understanding physical-chemical interaction during retrograde metamorphism. Enhancing the rate of such reactions is a proposed method for geologic CO2 storage, and perhaps for direct capture of CO2 from near-surface fluids. We review, synthesize, and extend inferences from a variety of sources. We include data from studies on natural peridotite carbonation processes, carbonation kinetics, feedback between permeability and volume change via reaction-driven cracking, and proposed methods for enhancing the rate of natural mineral carbonation via in situ processes (“at the outcrop”) rather than ex situ processes (“at the smokestack”). }, journal={Annual Review of Earth and Planetary Sciences}, author={Kelemen, P.B. and Matter, J. and Streit, E.E. and Rudge, J.F. and Curry, W.B. and Blusztajn, J.}, year={2011}, pages={545–576} }