EPSS Colloquium - spring-2025
The effect of a Paleoarchean meteorite impact on early surface environments and life
April 1, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Nadja Drabon - Harvard
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Large meteorite impacts strongly affected the habitability of the early Earth. The rocks of the Archean Eon record at least 16 major impact events with impactors larger than 10 km in diameter, and hence bigger than the dinosaur-killing Chixculub impactor. These impacts likely had severe consequences for the surface conditions and life during early Earth. I will present the analysis of sedimentary rocks across the 3.26 Ga S2 impact event (37-58 km impactor). The results reveal that the impact initiated a giant tsunami, evaporation of the uppermost layer of the ocean, and an increase in iron by mixing Fe2+-rich deep into Fe2+-poor shallow waters. Although meteorite impacts are usually seen as destructive and the S2 impact certainly had disastrous short-term consequences, it may have had some medium-term benefits for the early biosphere. The mixing of Fe²⁺ into the upper water column supplied electron donors to the photic zone, while an increase in weathering during the post-impact hothouse environment, as well as contributions from the bolide itself, injected phosphorus into the system. Overall, meteorite impacts, while destructive, may have had transient benefits for early life on Earth. [Here is a link to the paper: https://www.pnas.org/doi/abs/10.1073/pnas.2408721121
The chemistry behind slow earthquakes in subduction zones
April 8, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Cailey Condit - University of Washington
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In this talk I will compare petrologic models to the exhumed rock record of subduction zones to investigate the role of metamorphic and metasomatic processes in producing slow earthquakes (or Slow Slip Events) in subduction zones. I will show that metamorphic dehydration reactions in warm subduction zones releases ample water at the conditions of these slow earthquakes and provide a ready fluid source for the inferred high pore fluids invoked to facilitate these slip behaviors. I will also show these slow earthquakes are hosted within rheologically unique lithologies that form from metasomatic reactions catalyzed by these fluids. I will argue that it is through a combined chemical and mechanical perspective coupled with modelling and observations of the rock record that we can make progress in slow earthquake science.
Energetic particles, all the way down: how inner magnetosphere dynamics connect to aurora
April 15, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Allison Jaynes - University of Iowa
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Pulsating aurora is created by particle scattering in the equatorial magnetosphere through cyclotron resonance with chorus waves and constitutes a significant amount of energy transfer from the magnetosphere to the ionosphere. This process depends on a complex combination of the pre-existing source and seed populations, particle injections, and cold plasma structuring in the inner magnetosphere. Pulsating aurora can include precipitation up to MeV energies and is directly related to particle injections. It is also fairly ubiquitous and can be long-lasting and widespread. Due to the high energy nature of the precipitation, it can deposit energy in the middle and lower atmosphere. Thus, pulsating aurora investigations offer us an insight into total energy flux into the atmosphere and magnetosphere-atmosphere coupling. This presentation summarizes recent work to quantify the energy content of pulsating aurora and estimate total energy deposition into the atmosphere as well as understand the impact on the atmosphere of this highly energetic type of aurora.
Up from the depths: investigating enigmatic subduction zone processes using the Condrey Mountain Schist, northern California
April 22, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Carolyn Tewksbury-Christle - Fort Lewis College
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Slow slip and tremor (SST) events occur downdip of the megathrust in modern subduction zones and are collocated with seismic low velocity zones (LVZs) with seismic characteristics indicative of near-lithostatic pore fluid pressures (Pf). Multiple models exist for SST sources, but all require brittle failure and transient accelerated slip. Exhumed subduction complexes, such as the blueschist facies unit of the Condrey Mountain Schist (lower CMS), northern California, can help constrain potential SST sources. The lower CMS records distributed prograde viscous deformation at SST depths (460°C, ca. 1 GPa) across a primarily metasedimentary shear zone. Intercalated m- to km-scale mafic and serpentinized ultramafic lenses are comparable in length scale to modern tremor sources, and shear zone widths and seismic signatures are comparable with modern LVZs, suggesting the lower CMS may preserve fossil SST sources. To evaluate this possibility, we characterized serpentine and sodic amphibole rheology using macro- and microstructural observations, Raman spectroscopy, and Electron Backscatter Diffraction (EBSD) data. Sodic amphiboles record coeval brittle failure and diffusion creep and microboudinage, while antigorite records a combination of brittle and viscous mechanisms, including veins, glide, kinking, and pressure solution. Recently published flow laws for both predict complex non-Newtonian rheologies that could result in stain localization and acceleration in response to transient stress concentrations. Flow laws also predict potential brittle failure modulated by extremely high (near lithostatic) pore fluid pressures, consistent with the rock record, LVZs, and SST in modern subduction zones. Estimated tremor magnitude for these lenses using vein displacement and lens area is similarly comparable to modern tremor. These data collectively suggest that the lower CMS mafic and serpentinizedultramafic lenses are potential fossil SST sources.
The Power of Comparative Planetology to Decipher the History of Planetary Surfaces
April 29, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Mathieu Lapôtre - Stanford
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Landforms, shaped by interactions between environmental fluids and geologic surfaces, encode information about hydrology, climate, and the overall environment that may be preserved over geologic timescales. Thus, understanding the mechanics of geomorphic and sedimentary processes that shape the landscapes of planets is key to deciphering their respective paleoenvironmental records. To date, the majority of mechanistic models for surface processes were derived from observations of modern Earth, where life thrives, and from scaled-down experiments. Numerical models help to probe wider parameter spaces than can be achieved on our planet, but they only contain the physical rules that they were designed to honor in the first place. However, the foreign parameter spaces spanned by other planets may lead to phenomena that we do not realize need to be included in our models – the unknown unknowns. Even Earth would have looked alien to any of us before the advent of macroscopic life, with a different atmospheric composition and different surface sedimentary dynamics for example. As a result, the applicability of existing models for surface processes is often limited to those systems that most closely resemble modern terrestrial conditions, impeding our ability to reliably decipher the environmental records of other planets and the early Earth. Flipping this paradigm, planetary bodies in our Solar System and beyond span a range of sizes, environments, and compositions that allow us to approach comparative planetology as a full-scale experiment, where other bodies offer a unique opportunity to develop more robust models and expand their applicability. Knowledge gained from the exploration of other planets not only contributes to our fundamental understanding of surface processes, but at times can feed back into our understanding of the Earth. In this presentation, I will illustrate how a dialogue between the Earth and planetary sciences can increase our ability to interpret landscapes and rocks with three examples from our own Solar System – the formation of large eolian ripples under the thin martian atmosphere, the dynamics and record of unvegetated meandering rivers on the early Earth and Mars, and the alien organic-sediment cycle of Saturn’s moon, Titan.
A grand-tour of the Marine Deep Biosphere, Earth's final biological frontier.
May 6, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Gustavo Ramirez - Cal State LA
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The ocean subseafloor, comprised of deep marine sediment and sediment-buried crust, hosts a sizable fraction of the planet’s microbes and represents the volumetrically largest and most inaccessible habitat on Earth. In this underexplored, low energy, and ancient environment, microbial communities persist for hundreds of millions of years. Consequently, many questions about of this habitat emerge: what adaptations allow microbes to survive long time-scales, what are the energy sources, which evolutionary processes may be at work here, and what are the planetary-level repercussions of microbial life under the seafloor. Previous, on-going, and future efforts to address these questions by my laboratory will be discussed in a grand-tour of the marine deep biosphere.
The next geomagnetic reversal
May 13, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Bruce Buffett - Berkeley
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Historical records show that the strength of the geomagnetic dipole field has been decreasing at a rate of 6% per century. Extrapolating this historical rate into the future suggests that a geomagnetic reversal will occur within 2 kyr. Is there cause for concern? Here I use paleomagnetic observations and stochastic models to quantify the statistics of fluctuations in the dipole field. Using theoretical tools developed by Kolmogorov (renown for his work on turbulence) I show that an imminent geomagnetic reversal is very unlikely. A quantitative estimate for the reversal probability is about 2% in the next 20 kyr, rising to 11% after 50 kyr. I conclude the talk by showing why the linear extrapolation of the current historical rate is so unreliable.
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May 20, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Sidney Hemming - Columbia/ Lamont-Doherty
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May 27, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Wai Allen - ASU
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June 3, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Lindsay Schoenbohm - University of Toronto
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