Innocent Ezenwa, Carnegie Earth and Planets Laboratory
Electrical Resistivity, Thermal Conductivity and Melting of Fe Alloys at Planetary Core Conditions
February 3, 2023 at 3:00 pm (PLS 1140)
The global magnetic field of the terrestrial planets is generated by the action of the dynamo, with motions thought to be due to convection. For the Earth, compositional convection from the release of light alloying elements at the inner core boundary has been known to be the leading driver of the present-day geodynamo. The onset of the nucleation of the inner core has been estimated to be about 1.5 billion years ago whereas the magnetic field has been in existence for over 4.5 billion years, evidenced in paleomagnetic rock record. The early dynamo has been assumed to be powered thermally before the birth of the inner core. However, literature data from the past decade have raised skepticism in the generation and sustainability of a thermally driven early geodynamo. To closely access this phenomenon, the understanding of the transport properties of Fe and its alloys at core conditions are needed. In this talk, I will present the electrical resistivity, thermal conductivity and the melting processes of Fe and its alloys with light elements (e.g., Si, C, S etc.) at extreme pressure and temperature conditions.
Melissa Sims, Johns Hopkins University
Compression in Multiple Regimes: Studies of Plagioclase, Cu, and MgO
February 10, 2023 at 3:00 pm (PLS 1140)
Geoscience problems, from meteorite impacts to exoplanet interiors, require study of timescales that span orders of magnitude. However, the shock and static experiments required to examine these processes occur over limited timescales, strain-rates, and temperatures compared to natural systems. The effects of kinetics and strain-rate are relatively unconstrained. It is therefore important to understand their effects during the experiments used to determine phase diagrams and equation of state models. In meteoritic systems, understanding kinetic and strain-rate effects is vital due to the millisecond timescales of impact processes. For exoplanetary systems and the deep Earth, temperature, kinetics and strain-rate studies are important because rheological properties, such as viscosity, are dependent on phase identities and deformation mechanisms. In this presentation, I will discuss high pressure deformation and phase relations in plagioclase, copper, and MgO across compression regimes. In plagioclase, I examine the effects of compression-rate and kinetics on deformation, transition mechanisms, and subsequent phase formation using laser heated membrane driven compression. In copper, we compare computational work to laser shock experiments and examine textural changes across the fcc to bcc phase transition. In MgO, we examine the effect of temperature on the B1-B2 transition. We compare our ramp experiments to shock data collected along the Hugoniot and find differences in texture. These studies allow us to more accurately examine geological events with timescales from microseconds to billions of years.
Sean Peters, Middlebury College
The effects of unsteady eruption rates on lava flow morphology and propagation
February 17, 2023 at 3:00 pm (PLS 1140)
Eruption rate has a large impact on the morphology and propagation of lava flows, typically determining the surface texture and flow length, for instance. Laboratory analog experiments allow for the qualitative and quantitative analysis of flow dynamics and phenomenology. In Peters et al. , we addressed the effects of unsteady eruption rates by conducting 120 experiments where we extruded polyethylene glycol (PEG) wax into a chilled water bath in a plexiglass tank to simulate lava flow emplacement. We simulated unsteady eruption rates at the vent with a step-wise increase and decrease in eruption rate for either 10 or 50 seconds. We utilized the dimensionless parameter, Ψ - timescale of crust solidification/ timescale of lateral propagation - to classify flow morphology. Flow propagation was characterized with respect to three emplacement modes observed in real lava flows: breakouts (surface and marginal), inflation, and tubes. Among other insights, we found that different durations of increased or decreased eruption rate influence the type of marginal breakouts occurring and that presence of a coherent crust controls surface breakouts and inflation. This experimental approach can be expanded to investigate other aspects of flow emplacement.
Lucien Nana-Yobo, Texas A&M University
Strontium isotopic response during Oceanic Anoxic Event 2 (OAE 2)
March 10, 2023 at 3:00 pm (PLS 1140)
Ocean anoxic events are characterized by increased organic richness of marine sediment on a global scale with accompanying positive excursions in sedimentary organic and inorganic carbon isotope values. Increased supplies of nutrients to the oceans are required to sustain elevated levels of marine productivity necessary to account for high carbon export fluxes during ocean anoxic events. Submarine eruptions of one or more large igneous provinces are the proposed trigger for OAE 2, and the CO2 induced global warming and increased rainfall acidification are both factors that can increased continental weathering rates and therefore nutrient inputs to the oceans. On the other hand, seawater interactions with hot basalts at LIP eruptions sites can deliver ferrous iron and other metals and reduced gases to seawater that can stimulate increased productivity in surface waters and increased oxygen demand in deep waters. The relative importance of continental and submarine weathering drivers of expanding ocean anoxia during OAE 2 are difficult to disentangle. In this talk, we present a new high-resolution record of seawater 87Sr/86Sr in a pelagic carbonate succession from the Eagle Ford Formation in Texas. With the help of a box model of the ocean Sr cycle, and knowledge of the contrasting 87Sr/86Sr signatures of continental weathering and submarine weathering inputs of Sr to the oceans, the relative magnitudes of the continental weathering and submarine weathering fluxes of Sr to the oceans during OAE 2 is determined. Finally, the new 87Sr/86Sr data offers a significant refinement to the temporal pattern of changing 87Sr/86Sr in the global ocean over OAE 2.
Rasheed Ajala, Columbia University
Multiscale Earth models: Wavefield verification and space exploration
March 31, 2023 at 3:00 pm (PLS 1140)
Accurate Earth models are fundamental to the study of the composition, structure, and evolution of our planet. Over four decades have passed since the introduction of seismic waveform inversion, yet regional- and global-scale Earth models rarely exceed 0.2 Hz in frequency content. A primary impedance to progress is the computational demand for optimization on a large spatial domain. Urban seismology offers a paradigm shift through advancements in field instrumentation using dense local seismograph arrays and telecommunication cables to provide wavefield records with unprecedented detail. Artificial intelligence also shows promise in accelerating wavefield simulations. One tractable strategy then uses these datasets to develop high-frequency models, possibly exceeding 1 Hz in perceived regions of interest, and incorporate them into longer-wavelength reference Earth models. To illustrate some elements of these research ideas and implementation challenges, we employ a case study in southern California, where earthquake hazard assessment is paramount to the seismological community. Local Earth models with a better characterization of sedimentary basins and fault zones are assimilated into the most popular regional models of the area to enhance them. We further investigate the accuracy of the multiscale models by measuring the errors in their wavefield predictions using complete three-component broadband seismograms. Some of the improvements in the reference models indicate that the approach represents a suitable path forward pending the next technological leap in computing.
Rodney Tollerson II, Caltech
Feast or famine: Regulation of methane metabolism at low-energy biological systems
April 7, 2023 at 3:00 pm (PLS 1140)
Historically, model biological systems have been used to understand the mechanisms underpinning cellular physiology. These systems are selected for high growth rates and minimal energetic constraints, such as the bacteria Escherichia coli or the yeast Saccharomyces cerevisiae. While these organisms are of great utility in understanding the molecular mechanisms of general, strongly conserved pathways, they do not cover the breadth of microorganisms on our planet. This is especially true for microbes that live in low-energy environments such as oceanic sediments. In these conditions, microbes must rapidly and efficiently adapt to changes in their environment to take advantage of nutrient influx or protect themselves under stress conditions. My research focuses on how protein production is regulated in these environments, specifically focusing on methane-metabolizing organisms such as the anaerobic methanotrophic archaea (ANME) and the methanogen, Methanosarcina acetivorans.
Lindy Elkins-Tanton, School Of Earth and Space Exploration, ASU
The NASA Psyche Mission: An Electric Journey to a Metal World
April 21, 2023 at 3:00 pm (PLS 1140)
When our solar system was just an infant, thousands of planetesimals formed in fewer than one million years. Heat from the decay of the short-lived radioactive 26Al melted many planetesimals, allowing metal cores to differentiate from rocky mantles.
Over the next few tens of millions of years, many planetesimals crossed paths catastrophically. Colliding worlds merged into even larger planets, eventually forming a small number of planetary embryos. Models show that some destructive “hit and run” impacts strip the silicate mantle from differentiated bodies. This is the leading hypothesis for the formation of asteroid (16) Psyche’s formation: it is a bare planetesimal core.
But we all know that the solar system is more complex than we have been able to imagine, and there are many possible origins of Psyche based on the limited data we now have. Deep space missions, too, are almost unimaginably complex. In this talk I will introduce what is known and what is hypothesized about the asteroid Psyche based on the latest data, how we have planned a mission to an unknown object, how we progressed with the mission through COVID and what happened when our launch date slipped to October of 2023, and what we will measure and discover while our robotic spacecraft is orbiting the asteroid.
Cecilia Sanders, Johns Hopkins University
Interrogating the relationship between microbial ecology and taphonomy: A view through the phosphorite window
April 28, 2023 at 3:00 pm (PLS 1140)
The history of life is known by its records: body fossils, burrows and tracks, the fractionation of heavy and light isotopes between geological and biological materials. Microorganisms play an important role in the creation — and destruction — of all these records during initial deposition, early diagenesis and lithification. However, modern analogs suggest that microbial ecological structure may be particularly critical in the formation of ancient phosphate-rich sedimentary deposits ("phosphorites"). Phosphorites are among the most robust paleobiological records, often containing exquisitely preserved fossil organisms and being associated with major ecological and climatological transitions in geologic time. But are they representative of global perturbations to biogeochemical cycling? Or local factors that selected for particular microbial communities? In reconstructing the depositional setting and diagenetic history of different ancient phosphorite deposits at regional, local, and microscopic scales, we can test hypotheses about the relationship between microbial ecology and phosphorite formation. This talk will focus on the view through the phosphorite taphonomic window at the Precambrian-Cambrian Boundary, but hey! It's impossible to talk phosphorite without also talking a little bit about dinosaur poop.
The coordinator for the Colloquium Series is Dr. Megan Newcombe. You can contact her at newcombe [at] umd [dot] edu.
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