EPSS Colloquium - spring-2022


Lost continents and preserved primordial reservoirs: A history both ancient and deep

March 29, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Matt Jackson - UCSB
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Plate tectonics injects continental and altered oceanic crust into the mantle. This process facilitates communication between shallow terrestrial reservoirs—lithosphere, hydrosphere, and atmosphere—and Earth’s deep interior over geologic time. Geochemists trace this communication with a variety of novel tools. A key result of this effort reveals that subducted crust constitutes a significant reservoir in the Earth’s mantle that is sampled by buoyantly upwelling mantle plumes that source volcanic hotspots, but the location, and age, of this deep crustal reservoir is poorly constrained. Using constraints from seismology in tandem with the geographic distribution of geochemical signatures in volcanoes at the Earth’s surface, the geochemical structure of the mantle is becoming clearer. A key observation made by combining seismic and geochemical constraints is that subducted continental crust is isolated in the southern hemisphere mantle, while oceanic crust is located everywhere. This spatial pattern can be explained as the result of the time evolution of tectonic processes operating at Earth’s surface: oceanic crust subduction began in the Archean or early Proterozoic, and oceanic crust has since been subducted at all latitudes over geologic time; in contrast, continental crust subduction began in the late Neoproterozoic—when the Gondwana-Pangea supercontinent was assembling in the southern hemisphere—helping to explain why subducted continental crust is limited to the southern hemisphere mantle. This model implies a recent formation of the austral mantle subducted continental crust domain, and the excess radiogenic heat from this deep continental crust reservoir may explain why there are twice as many austral hotspots as boreal hotspots. Finally, while I seek signatures of ancient surface-derived materials in igneous rocks, in a parallel effort I prospect for signatures of early-Earth reservoirs that have survived being overprinted by subducted crust since shortly after terrestrial accretion. Surviving relics of Earth’s earliest history are found in lavas with primordial noble gas signatures, and the origin of these signatures dates to the earliest Hadean. Applying novel nucleosynthetic and short-lived radiogenic isotope systems to rocks sampling these terrestrial primordial domains will provide further insights into the earliest evolution of the planet.


Origin of moons in the solar system and beyond

April 5, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Miki Nakajima - University of Rochester
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The Apollo lunar samples reveal that Earth and the Moon have strikingly similar isotopic ratios, suggesting that these bodies may share the same source materials. This leads to the "standard" giant impact hypothesis, suggesting the Moon formed from a disk that was generated by an impact between Earth and a Mars-sized object. This disk would have had high temperature (~ 4000 K), and its silicate vapor mass fraction would have been ~20 wt %. However, impact simulations indicate that this model does not mix the two bodies well, making it challenging to explain the similarity. In contrast, recent studies suggest that more energetic impact models that produce higher vapor mass fractions (~80-90 wt%) could mix the two bodies, naturally solving the problem. However, these energetic models may have a challenge during the Moon accretion phase. Our analyses suggest that km-sized moonlets experience a strong gas drag from the vapor portion of the disk and fall onto Earth in a very short timescale. This problem could be avoided if large moonlets (>1000 km) form very quickly by the process called streaming instability. We investigate this possibility by conducting numerical simulations with the code called Athena. We will discuss implications of this study for moons in the solar system and extrasolar systems (exomoons). We will also briefly mention our ongoing work on terrestrial craters and shock experiments at the University of Rochester.


Deep-sea mining: treasure versus destruction in oceans' most pristine ecosystems

April 12, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Craig Smith - University of Hawaii at Manoa
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: Interest in mining the deep-sea floor in international waters is growing rapidly due to growing demands for metals for green technological (e.g., cobalt for electric vehicle batteries). Currently, there are 32 mineral exploration contracts registered with the International Seabed Authority (the management body for mining in areas beyond national jurisdiction), and commercial mineral extraction may begin within 2-3 years. I will briefly review the three major types and distributions of deep-seafloor minerals (massive sulfides, cobalt-rich seamount crusts, and polymetallic nodules), and then focus on polymetallic nodules, which contain vast resources of cobalt, nickel and copper, and are first in line for commercial exploitation. Nodule mining will focus on abyssal Pacific seafloor habitats characterized by very low resilience, high biodiversity, and recovery times of decades to millions of years from mining disturbance. Mining will remove and bury seafloor habitats, and is expected to generate sediment plumes and noise pollution extending hundreds of kilometers in the water column. If conducted at scales required to supply a global fleet of electric vehicles, nodule mining could damage 1.5 million square kilometers (an area equal to Germany, France, Spain and Portugal combined), causing species extinctions and threatening ecosystem services. I will also discuss environmental conservation measures adopted for nodule mining and highlight knowledge gaps hindering the prediction and management of mining impacts on ocean ecosystems.


Subsurface Landscapes of Oxidation and Reaction in the Critical Zone

April 19, 2022
3:30 p.m. - 5 p.m.
Zoom/Virtual

Presented By:

  • Sue Brantley - Penn State
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Water, gas, and biota interact with bedrock to create and maintain the mantle of altered material known as regolith within Earth’s critical zone. This mantle in turn feeds human and non-human ecosystems and affects water flow and storage. However, our understanding of how regolith forms from bedrock is poor at best. Two features of regolith combine to make it difficult to develop successful quantitative models of weathering: the extreme heterogeneity of weathered materials and the coupled nature of chemical, physical, and biological (including anthropogenic) regolith formation factors. In this talk I will discuss the use of geochemical and geophysical tools to learn how the deep architecture of the critical zone – including the distribution of subsurface reaction fronts developed through weathering reactions – may control water storage and flow. I will pair geochemical observations made on shale hillslopes with geophysical measurements to develop better models for hydrologic behavior and soil formation. The long-term goal is to stop treating the subsurface as a black box but to begin to understand how it acts as a (self-organizing?) system that we can understand and protect.


Sea level of the past and future: At the Intersection of Politics, Race, Gender, Ice Sheets, and Corals

April 26, 2022
3:30 p.m. - 5 p.m.
Zoom/Virtual

Presented By:

  • Andrea Dutton - University of Wisconsin
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My research centers on reconstructing past changes in sea level to better understand the dynamics of ice sheet and sea level response to changes in climate, particularly during warm climates or rapid climate transitions. I will present an overview of our evolving understanding of sea level and ice sheet volume during the Last Interglacial, ~125,000 years ago, through work that my research group has conducted at numerous sites around the globe. This interdisciplinary work relies on using fossil corals to reconstruct the past position of sea level through field work that is integrated with sedimentology, isotope geochemistry, reef paleobiology, and geophysical modeling. In addition to sharing some of this emerging science, my talk will also explore the ways in which my research and my experience as a scientist is impacted by and/or has ramifications for several intersecting issues, including politics, race, and gender.


Imaging latent crustal fluid injection transients in Southern California

May 3, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Zach Ross - CalTech
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Earthquake swarms are primarily manifestations of aseismic driving processes that occur transiently. We study the spatio-temporal distribution of these aseismic processes in Southern California using a 12-year earthquake catalog derived with deep learning algorithms. In a core portion of the plate boundary that is not associated with magmatism, we identify nearly one hundred swarms that have durations in the range of 0.5-6 years. These swarms are not directly driven by tectonic processes, yet constitute about 1/4 of the total seismicity. We find that about half of the swarms exhibit ultra-slow diffusive migration patterns, along with propagating backfronts, in which a shut-down of seismicity propagates away from the source region. These observations are all consistent with expectations for natural fluid injection processes. The chronology of the swarms indicates that these aseismic driving processes were active in some part of the region throughout 2008–2020. The observations challenge common views about the nature of swarms, which would characterize any one of these sequences as anomalous. The regional prevalence of these sequences suggests that transient fluid injection processes play a key role in crustal fluid transport.


Super-Earths' Composition Constraints Planet Formation Pathways

May 10, 2022
3:30 p.m. - 5 p.m.
TBD

Presented By:

  • Diana Valencia - University of Toronto
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It is now firmly established that planets with masses less than 10 earth-masses are the most common astrophysical objects in the galaxy. In 2009, CoRoT-7b and Kepler-10b became the first low-mass exoplanets with a measured radius and mass, and thus the first ones for which we could infer their bulk composition. With space missions Kepler and recently TESS, the database of small planets with measured masses and radii has grown, albeit slowly, due to the inherent difficulties in measuring the mass of small exoplanets. We are finally at a point where we can study these planets in a population sense, and understand their characteristics. I will discuss what we have learned in terms of the composition of these planets, how this information constrains our understanding of their formation, and how it compares to our Solar System understanding.


The deep Earth redox engine

May 17, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Susannah Dorfman - Michigan State
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Over geologic time, exchange of volatiles such as CO2 and H2O between the Earth’s deep interior and surface have set the composition of our habitable atmosphere, facilitated plate tectonics, and driven the dynamo in Earth’s core. At depth within the Earth, volatiles encounter not only a gradient of increasing pressure and temperature, but also chemical stratification with decreasing availability of oxygen. These differences in conditions stabilize different mineralogy and forms for storing volatiles. I will discuss experiments on the chemistry and physical properties of minerals in Earth’s mantle containing important redox-sensitive elements iron and carbon. As the major element with most complex redox behavior, iron is a key indicator of Earth’s redox conditions, and the seismic properties of iron-bearing minerals could reveal heterogeneous redox conditions in inaccessible depths of Earth’s mantle. Carbon is challenging to trace using geophysical methods, but deep carbon cycling provides us with the deepest-originated samples of the Earth: diamond inclusions. For these problems, developing experimental approaches to control of redox conditions and measurement of chemistry for miniaturized samples is essential. The results of these experiments allow us to understand deep Earth volatile cycles based on geochemistry and geophysics.


The rise of wildfire disasters in the 21st century: what have we learned?

May 24, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Crystal Kolden - UC Merced
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The rise of wildfire disasters in the 21st century: what have we learned? ABSTRACT : For most of the 20th century, the study of wildfires was dominated by ecologists and foresters, with much emphasis placed on understanding the natural role of fire in ecosystems and the physics of wildfire behavior in order to prevent firefighter fatalities. In the last two decades, however, we have seen the rise of the wildfire disaster, with widespread negative impacts to complex social-ecological-technological systems globally. What lessons have these disasters yielded, and what critical scientific gaps have they exposed? Wildfires present a unique type of disaster, different from all other disasters due to the both the singular relationship that humans have had with fire for millennia and our active and ongoing alteration of the landscape and the broader Earth system. Historically, fire science has maintained an event-focused perspective that sees fires only as a tear in the fabric of the Earth system, rather than as an integral thread in that fabric. As a result, the solutions proposed and enacted have also been event-focused, leading to outcomes that reinforce feedback loops and further exacerbate social inequalities and irreversible losses. Here, I examine the lessons learned from wildfire disasters and how those lessons can be applied in an interdisciplinary framework to develop more comprehensive solutions to live with wildfire.


New insights into lowermost mantle dynamics from observations and models of seismic anisotropy

May 31, 2022
3:30 p.m. - 5 p.m.
3853 Slichter Hall

Presented By:

  • Maureen Long - Yale
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Mantle convection and its surface manifestation, plate tectonics, are fundamental to Earth’s evolution. Observations of seismic anisotropy, or the directional dependence of seismic wavespeeds, provide some of the most direct constraints on the pattern of convective flow in the Earth’s mantle. Seismic anisotropy analysis is routinely applied to study upper mantle processes, leading to fundamental discoveries about the patterns of flow in the upper mantle and the drivers of that flow. There is also convincing observational evidence for seismic anisotropy in the lowermost mantle; however, it has proven challenging to develop reliable frameworks for accurately measuring D” anisotropy and for interpreting these measurements in terms of mantle flow patterns. Despite the challenges, however, observations of lowermost mantle anisotropy have the potential to shed light on a number of fundamental unsolved problems relating to deep mantle structure and dynamics, such as the origin and evolution of large low shear velocity provinces (LLSVPs) and the role that subducting slabs play in lowermost mantle processes. This talk will describe a set of studies aimed at measuring and interpreting seismic anisotropy at the base of the mantle, using a combination of tools and approaches. These include the development of new strategies for measuring shear wave splitting due to D” anisotropy, the modeling of D” anisotropy using global wavefield modeling approaches, the incorporation of new results from mineral physics into the interpretation of D” anisotropy, and comparisons between geodynamic model predictions and seismic measurements.