A New Perspective on the Late Ordovician Mass ExtinctionBy Mónica Alejandra Gómez CorreaEdited by Karla Bugarin Earth has experienced mass extinction events, which have been caused by volcanism, meteorite impacts, and climate change. Particularity, the Late Ordovician Mass Extinction (LOME) was the first of the big five extinction events that have affected metazoan life in Earth’s history (Sepkoski, 2002), identified by an abrupt decrease in the diversity trend after the Great Ordovician Biodiversification Event (GOBE), encapsulating the most significant increase. In recent decades, studies have aimed to decrypt the biological signal shown by the fossil record during the LOME, assess the timing and duration of the event, and clarify its link to environmental changes. In February 2019, Rasmussen et al. presented a biodiversity curve with four times higher resolution than previous authors (e.g., Alroy et al., 2008 and Sepkoski, 2002) for the Early Paleozoic (540 to 420 million years) and compared this curve to potential controlling variables such as temperature, sea-level change, oxygen in the atmosphere, plate tectonics, and carbon cycle. The biodiversity curve for the earliest Paleozoic periods (Cambrian, Ordovician, and Silurian) showed gradual biodiversity increases within two radiation events, the Cambrian Explosion and GOBE, and a 10 to 12 million years long extinction interval, identified as the LOME. In order to estimate biodiversity in time bins of 2.3 million years, Rasmussen and his colleagues (2019) used two different datasets of more than 185,000 fossil occurrences each, filtered from the raw data registered in the Paleobiology Database and binned in the time slices manually or automatically. The two datasets were standardized by using methods such as classical rarefaction and shareholder quorum subsampling. Based on these two standardized datasets, the authors calculated richness trends using Alroy’s approach (DSQS), Hill number or Shannon’s entropy adapted by Chao et al. (DHill), and a capture-recapture model built from a subset of ca. 25,000 occurrences and fitted to a “superpopulation approach” by using Laake’s interface (DCR). The trends obtained were similar (Figure 1). Especially, those generated by DSQS and DHill approaches showed more coincidence because both methods are designed to compare samples of equal completeness. At the same time, they presented higher volatility than DCR due to uneven sampling. In addition, the curve of probability-based diversities (DCR) differed radically in magnitude from DSQS and DHill confirming a rising richness tendency from Cambrian to Middle Ordovician. However, in contrast to previous curves, it showed stepwise changes during the Early Paleozoic instead of abrupt increases and decreases. Traditionally, the LOME is an event that occurred around 450–440 million years ago and eradicated nearly 85% of the marine species in a two-phased episode. The first phase happened in the late Katian, affecting organisms that lived in the shallow and deep water column, and the most devastating second phase, in the late Hirnantian, impacting the fauna in different water depths. The biodiversity curve presented by Rasmussen et al. (2019) showed three major drops starting in the mid-Katian, suggesting not only a new phase of extinction but also an earlier onset of the LOME and implying that the global hyperthermal event in the late Katian, the Boda Event, as well as the faunal dispersal and migration event, known as Richmondian Invasion, might be included as part of the LOME. Previously, the LOME had been attributed to cooling and warming variations in a short period and potential glaciation in a large portion of the terrestrial surface. However, Rasmussen et al. (2019) suggest a new perspective on the causes of the LOME and link the event to intensive volcanism that increased temperature, elevated the CO2 levels in the atmosphere and ocean, and triggered the first extinction phase. In addition, the authors include the Boda Event and Richmondian Invasion in the interval as periods when environmental conditions favored migration of fauna towards open niches in colder and deeper waters and enhanced existing species to broaden their geographic ranges. These migration events potentially buffered the effects of the volcanic event on the fauna, which later was affected by the greenhouse to icehouse fluctuations that, combined with the paleogeographic configuration, had a devastating effect on the organisms at the end of the Ordovician. Although the authors (Rasmussen et al., 2019) showed estimates of biodiversity for the Early Paleozoic in high-resolution by implementing a sophisticated new method, which accounts for not only sample completeness but also for survival, preservation, and origination probabilities, the correlation-causation approach for the biodiversity trends and the environmental variables could be improved by integrating higher resolution information to the analysis. In particular, further research regarding the LOME should estimate the extinction rates during the three phases to determine when the major loss in taxa happened and incorporate model selection to identify the drivers of the mass extinction when evaluating multiple causes for biodiversity trends. In this sense, it is also essential to extend Rasmussen et al.’s approaches to re-assess biodiversity throughout all geological time and continue testing their capture-recapture model. References
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Preguntas abiertas y cambios de paradigma en geociencias Escrito por Luisa F. Zuluaga Editado por Angela Ara La ciencia y el avance en el conocimiento son tareas que nunca terminan, cada respuesta genera nuevas preguntas. Las geociencias no son la excepción. A manera de ladrillos y cemento, vamos poco a poco usando conocimiento previo para resolver nuestras preguntas, creando construcciones cada vez más grandes y complejas, ojalá más robustas. Nuestras "construcciones de conocimiento" nos sirven para predecir fenómenos, avanzar en la tecnología, en fin, progresar. Apilamos sobre ellas, pero llega un punto en el que cada nuevo ladrillo es más complicado de encajar. En este momento se necesita de un nuevo paradigma, nuestra torre tiene que inspeccionarse, y si es preciso, desmontar completamente para dar paso a otra nueva y mejor manera de entender nuestro entorno. Recientemente publica la Academia Nacional de Ciencia Estadounidense su visión de oportunidades de investigación en geociencias para la década que apenas comienza A Vision for NSF Earth Sciences 2020-2030: Earth in Time [1]. El documento presenta las siguientes 12 preguntas:
*La Zona crítica es la parte más somera y reactiva de la corteza en tierra firme, comprende la capa de vegetación, pasando por los suelos y capas de roca fresca, incluyendo el fondo de aguas subterráneas activas (NRC, 2001; Sullivan et al., 2017) Algunas preguntas sorprenden a simple vista, podrían llegar a pensarse ya resueltas, o al menos eso parecía en nuestros estudios iniciales; pero al investigar detalladamente, surgen nuevas brechas en el conocimiento, y nuevas oportunidades de investigación aparecen. Interdisciplinariedad, diversidad y desarrollo Este tipo de documento es muy consultado por grupos de investigación, no solo por su valor científico, sino porque el investigar en estas preguntas mejora las posibilidades de recibir financiamiento gubernamental. Estos paneles y sus reportes son muchas veces directrices en ciencia, influenciando decisiones y políticas públicas. ¿Cómo cambiarían estas preguntas si estos paneles fueran más diversos, no sólo en términos de disciplinas, sino en experiencias vividas? ¿Cambiaría el orden de prioridades? ¿Aparecerían nuevas preguntas? Las últimas décadas han proporcionado más oportunidades para que personas tradicionalmente excluidas o poco representadas en el mundo de la investigación científica puedan avanzar. De hecho, un estudio reciente documentó el impacto positivo de sus innovaciones, que paradójicamente no resultan en un mayor reconocimiento de est@s científic@s [2]. Hay todavía mucho que hacer para superar obstáculos y explotar este potencial. Las geociencias observan el presente como clave del pasado, primordialmente en función de su avance a futuro, pero este futuro sólo será sostenible cuando de manera estructural todos contribuyamos y nos beneficiemos del avance geocientífico. En este reajuste se está gestando nuestro próximo cambio de paradigma [3]. ¿Serás parte de él o te quedarás fosilizado en un miogeosinclinal? Trabajo interdisciplinar, Diversidad y Desarrollo. Preguntas de prioridad científica ilustradas sobre la Tierra primordial (antes de haberse desarrollado su núcleo sólido, a la izquierda), que evoluciona a una Tierra dinámica (parte inferior derecha). En el inserto se resaltan procesos de superficie. Ilustración cortesía de Fabio Crameri et al., (NSF report figure 2-1, 2020) Referencias [1] A Vision for NSF Earth Sciences 2020-2030 National Academies of Sciences, Engineering, and Medicine. 2020. A Vision for NSF Earth Sciences 2020-2030: Earth in Time. Washington, DC: The National Academies Press. https://doi.org/10.17226/25761 [2] The Diversity–Innovation Paradox in Science. Bas Hofstra, Vivek V. Kulkarni, Sebastian Munoz-Najar Galvez, Bryan He, Dan Jurafsky, and Daniel A. McFarland PNAS April 28, 2020 117 (17) 9284-9291; first published April 14, 2020 https://doi.org/10.1073/pnas.1915378117 [3] Action Plan from All Professional Geoscience Societies and Organizations https://www.change.org/p/geoscientists-call-for-a-robust-anti-racism-plan-for-the-geosciences
Unsolved Questions and Paradigm Shifts in GeoscienceBy Luisa F. ZuluagaEdited by Ángela Ara Science and knowledge are never finished, each new answer brings forward new questions. Geosciences are not the exception. Little by little we use our previous knowledge to solve our problems and questions, much like brick and mortar, we create ever complex and bigger buildings, hopefully robust ones. Our ‘knowledge buildings’ serve us to predict phenomena, advance technology, in short, to progress. We pile on top of them, but at some point each new brick is more difficult to place. This stage suggests that a new paradigm is needed, forcing our buildings to be inspected, reassessed, and sometimes entirely dismantled in order to give way to novel and better ways to understand our world. The National Academy of Sciences (U.S.A) recently published its vision regarding research opportunities in geoscience for the starting decade: A Vision for NSF Earth Sciences 2020-2030: Earth in Time [1] The document presents the following 12 questions:
*The critical zone is the reactive skin of the terrestrial Earth, extending from the top of the vegetation through the soil and down to fresh bedrock and the bottom of actively cycling groundwater (NRC, 2001; Sullivan et al., 2017) Some of them may surprise at first glance, they were thought as more or less resolved; at least it seemed so in our introductory courses. But, while investigating them, new knowledge gaps are found and novel research opportunities arise. Interdisciplinary, Diversity and Development This type of document is widely consulted by research groups, not only due to its scientific value, but also due to the likelihood to receive grant funding while focusing on those questions. These panels and reports become science guidelines, influencing decisions and policy. How would these questions change had the panels writing them were more diverse? Not only in terms of discipline but also in terms of lived experiences? Would the range of priorities change? Would novel questions arise? The last few decades have provided more opportunities for people traditionally excluded or underrepresented in the world of scientific research to move forward. In fact, a recent study documented the positive impact of their innovations, but paradoxically, this does not result in better recognition of such scientists [2]. There are still hurdles and more to be done to unleash this potential. Geoscience observes the present as the key to the past, mainly as a function to advance in the future, but this future will only be sustainable when structures are in place for everyone to equally contribute and benefit from advances in geoscience. In this readjustment is where our next paradigm shift will emerge[3]. Will you be part of it or will you rather stay fossilized in a miogeosyncline? References [1] A Vision for NSF Earth Sciences 2020-2030 National Academies of Sciences, Engineering, and Medicine. 2020. A Vision for NSF Earth Sciences 2020-2030: Earth in Time. Washington, DC: The National Academies Press. https://doi.org/10.17226/25761 [2] The Diversity–Innovation Paradox in Science. Bas Hofstra, Vivek V. Kulkarni, Sebastian Munoz-Najar Galvez, Bryan He, Dan Jurafsky, and Daniel A. McFarland PNAS April 28, 2020 117 (17) 9284-9291; first published April 14, 2020 https://doi.org/10.1073/pnas.1915378117 [3] Action Plan from All Professional Geoscience Societies and Organizations https://www.change.org/p/geoscientists-call-for-a-robust-anti-racism-plan-for-the-geosciences
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Editors-In-ChiefsAngelique Rosa Marín Archives
June 2021
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