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Online Seminars & Events

Week of April 5, 2021
MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY
GPS Division Seminar
12:00 pm to 1:00 pm
DIX Planetary Science Seminar
4:00 pm to 5:00 pm
Environmental Science and Engineering Seminar
4:00 pm to 5:00 pm
Geoclub Seminar Series
4:00 pm to 5:00 pm
Seismo Lab Seminar
4:00 pm

Division Seminar

Mondays from 12:00pm to 1:00pm
For more information, please contact: Leticia Calderon

" Spectroscopy on Venus: Peeking through Clouds at the Hot Surface "

Darby Dyar

Abstract:

How old is the surface of Venus, and what rock types are present? Answering these fundamental questions presents a formidable challenge due to a lack of data and the thick CO2-rich atmosphere that shrouds The Venus surface. In fact, little is known about its surface geochemistry or mineralogy beyond results from Soviet landers in the 1970's and ‘80's. Spectroscopic characteristics of likely Venus surface rocks at 460°C are poorly constrained, as are the rock types and degree of surface-atmosphere interactions. How is it possible that we know so little about Earth's twin, and the most likely model for exoplanets in our Solar System?

This talk surveys what the outdated spectra and geochemical data from the Soviet landers can tell us about Venus. It reviews modern proof-of-concept data from the VIRTIS instrument on Venus Express, which demonstrated that tiny windows in the CO2 spectra of the Venus clouds do permit orbital observations, albeit of very narrow bands. Machine learning techniques are used to interpret new analog laboratory data acquired at Venus temperatures and apply them to the task of interpreting the rock type and alteration state of the Venus surface. Results place important constraints on the geologic past and likely age of the Venus surface, and highlight the need to return there with modern technology to address the many outstanding questions.

"Modeling the emergence of ancient metabolism"

Josh Goldford, Physics of Living Systems Fellow, Department of Physics,Massachusetts Institute of Technology

Abstract:

The transition from prebiotic chemistry to a complex biochemical network capable of sustaining life on early Earth is a major unresolved enigma. It is unclear how metabolism could have originated, given the limited geochemical availability of complex biomolecules in ancient environments. By integrating multi-scale network analysis, physicochemical constraints, and key assumptions regarding the composition of ancient biomolecules and environments, we reconstructed plausible trajectories of metabolic evolution and found that essential metabolic precursors for modern-day living systems may have not been necessary components for the earliest metabolic networks. Our results suggest that phosphate, fixed nitrogen and low potential electron donors may have been preceded by a simpler thioester and redox-driven organosulfur-based network capable of producing ancient molecular catalysts and lipids. Altogether, our work suggests that present-day metabolic networks may contain vestiges of a very ancient past, and that quantitative modeling can shed light on the environmental constraints that shaped ancient living systems.

Bio:

Josh Goldford is a Physics of Living Systems Fellow in the department of Physics at Massachusetts Institute of Technology. He completed his Ph.D. in the Bioinformatics Program from Boston University, and his M.S. in Microbial Engineering from the University of Minnesota. He uses theory and computational modeling to study how the environment constrains the evolution of metabolic networks and shapes the structure microbial communities.

DIX Planetary Science Seminar

Tuesdays at 4:00 pm
For more information, please contact Aida Behmard

"Revealing the Bulk Compositions of Small Planets"

Mike Greklek-McKeon, Graduate Student – Department of Planetary Science, California Institute of Technology

Abstract: Planets transiting nearby M dwarf stars are the best laboratory we have to study exoplanets with terrestrial sizes, compositions, and insolation levels. Transit surveys indicate that M dwarfs frequently host small planets orbiting in or near the habitable zone, and M dwarfs dominate the population of stars in the local solar neighborhood. However, it is unclear how the properties of small planets orbiting M dwarfs might differ from those of the terrestrial worlds in our own solar system. M dwarf planets could accrete significantly larger amounts of water because the ice line of their host star is closer in, and could be more likely to host massive volatile-rich atmospheres; but they might also be less likely to retain those atmospheres due to the high activity levels of their host star. We can explore the possible formation and evolution histories of these planets by measuring their masses and radii, which we can use to determine bulk densities that reveal the atmospheric mass fraction and possible bulk compositions of the planets. The TESS mission has discovered many dynamically interacting multi-planet M dwarf systems, and even one or two follow-up observations with space-like photometric precision is enough to determine the masses of these planets with transit timing variations (TTVs). I will discuss an example case of using Palomar observations to constrain the masses and bulk densities of planets with TTVs, and then make some predictions about our upcoming observations that will extend this method to small M dwarf planets.

"How did Mars' surface become uninhabitable?"

Edwin Kite, Assistant Professor – Department of Geophysical Sciences, University of Chicago

Abstract: What allowed rivers and lakes on Early Mars, which received just 1/3 of the modern Earth's insolation? And why did Mars' surface become uninhabitable? Data from rovers and orbiters have revealed a rich stratigraphic record of climate-sensitive deposits, allowing models to be tested. We have found that the greenhouse effect of high-altitude water ice clouds is a possible explanation for the warm climates – but only if the surface was arid, consistent with the geologic record. A new synthesis of geologic data and models suggests that water loss, CO2 loss, and loss of non-CO2 greenhouse forcing combined in surprising ways to set Mars' habitability trajectory. While lake-forming climates on Mars occurred over a time span of >1 Gyr, now Mars's surface is too cold and dry for life. I will discuss ways in which Martian surface habitability could be re-enabled.

Environmental Science and Engineering Seminar

Wednesdays from 4:00pm to 5:00pm
For more information, please contact: Bronagh Glaser

"Lacustrine records of Cenozoic and Plio-Pleistocene hydroclimate change in western North America"

Daniel Ibarra, University of California Berkeley

Abstract: Studies of Lake Bonneville in the late 1800s initiated over a century of research on Quaternary lakes in the American west. The continuation of this work is increasingly pertinent with the need to test climate models used to forecast future water resources in the region as the climate warms, resulting in a renewed focus on older lake systems. Importantly the presence or absence of lakes in terminal basins provide an unequivocal measure of wetness. In this work I will show that wetter conditions during both colder- and warmer-than-present periods in the past are recorded in shoreline and outcrop data from the latest Pleistocene and the middle-Pliocene. Using hydrologic scaling relationships, I demonstrate that: 1) Pleistocene lakes during glacial maxima in the northern Great Basin do not require substantial precipitation increases to explain many lake shoreline extents; and 2) middle-Pliocene lakes would have required up to a doubling of precipitation in the southern Great Basin. These inferences provide quantitative targets for assessing the performance of climate model simulations of the terrestrial water cycle. Additionally, I will show ongoing work that is part of my postdoctoral research testing these modeling results using carbonate clumped isotope paleothermometry and lacustrine chert triple oxygen isotope analyses to constrain past water balance in Pliocene and Eocene lake systems in the western

"Volatile organic compound emissions from Arctic ecosystems"

Riikka Rinnan, University Copenhagen

Abstract: Arctic areas are experiencing amplified climate warming that proceeds twice as fast as the global temperature increase. The rising temperature is already causing evident alterations, e.g. changes in the vegetation cover as well as thawing of permafrost. Climate warming and the concomitant biotic and abiotic changes are likely to have strong direct and indirect effects on the production and emissions of volatile organic compounds (VOCs) from arctic ecosystems. We have used long-term field manipulation experiments to assess effects of climate change on tundra VOC emissions. In these experiments, we have observed emission increases by a factor of 2-5 under experimental warming, and this strong temperature response has also been confirmed by ecosystem-scale data. In this talk, I present our recent findings on how VOC emissions in high latitude ecosystems are affected by permafrost thaw, insect herbivory and climate change.

"Recycling of Moisture in the Amazonian Basin and Possible Impacts of Future Deforestation"

Francina Dominguez, University of Illinois at Urbana-Champaign

Abstract: Climatologically, between 20 and 40% of the precipitation that falls over the Amazon basin comes from transpiration from the dense canopy and evaporation from soils within the forest itself. However, estimating the local terrestrial contribution of moisture at an intra-daily timescale is not easily done with existing methods. New water vapor tracers embedded within the Weather Research and Forecasting (WRF) atmospheric model allow us to "tag" the moisture that originates from the Amazonian basin and track it in space and time as it moves through the atmosphere and eventually rains out of the atmospheric column. This tool allows us to analyze detailed processes that occur at much smaller spatial and temporal scales than previously studied.

Geoclub Seminar Series

Thursdays from 4:00pm to 5:00pm
For more information, please contact: Sarah Zeichner

"U-series dating of giant avian eggshells from Pleistocene terrestrial strata"

Elizabeth Niespolo, Postdoctoral Scholar, California Institute of Technology

Abstract:

Many Middle-Late Pleistocene paleoanthropological sites beyond the ~50 thousand year (ka) 14C limit remain poorly constrained in time or undated entirely. Yet, they host key evidence about human evolution, including the earliest occurrences of H. sapiens, the development of modern human behaviors, and the geographic range expansion of H. sapiens out of Africa. 230Th/U dating, a type of Uranium (U) series dating, has about ten times the range of 14C dating and is commonly applied to carbonates that form in fluids hosting trace amounts of U. Ostrich eggshells (OES) are made of ~2-mm thick, low-Mg calcite, and in Africa and Eurasia, humans utilized giant ostrich eggs and their shells for food and personal uses (such as for tools and/or beads), so eggshells are frequently found in prehistoric archaeological/paleontological contexts. However, like the tissues of most higher animals (and unlike corals), these biominerals contain no primary U in them. I will introduce a novel approach to dating ostrich eggshell, called "230Th/U burial dating", applied to eggshells recovered from African archaeological sequences. 230Th/U burial dating of OES explicitly recognizes that U in OES is acquired from soil pore water, and OES yield accurate 230Th/U ages when corrected for prolonged U uptake. 230Th/U burial ages near and beyond the 14C limit on suitable eggshells preserve stratigraphic order and agree with independent dates. An example of the potential of the technique is shown at a site called Ysterfontein 1, a Middle Stone Age shell midden in South Africa, where 230Th/U burial ages indicate it is ~120 ka, making it not only the oldest shell midden known, but also the earliest evidence of systematic coastal foraging by humans. This promising new approach opens the door for dating Pleistocene terrestrial strata hosting ostrich and other giant avian eggshells in Africa and beyond.

"Origin and evolution of fumarolic gases from the magmatic-hydrothermal system at Guallatiri volcano, northern Chile"

Manuel Inostroza, Universidad Católica del Norte (Chile)

"TBD"

Cailey Condit, University of Washington

"TBD"

Dawnika Blatter, USGS California Volcano Observatory

Seismo Lab Seminar

Fridays from 4:00 pm to 5:00 pm
For more information, please contact Seismo Seminar Committee.

"Crustal Deformation Revealed by Complex Rupture Modeling and Seismic Observations"

Prof. Roby Douilly (UC Riverside)

ABSTRACT:
In my Observational and Computational lab, we use seismic source imaging technique to derive crustal properties and we also use dynamic rupture simulation to investigate the effects of complex fault systems on rupture path during an earthquake. In this talk, I will discuss a recent and ongoing studies on dynamic models of earthquake rupture in CA and seismic imaging in Nepal, with a focus on crustal faulting.
In the case study of the rupture modeling in the eastern San Gorgonio Pass region in CA, we examined the effect of different assumptions about fault geometry and initial stress pattern on the dynamic rupture process to test multiple rupture scenarios. We find that a rupture on the Coachella segment is more likely to branch to the Mission Creek rather than to the Banning fault strand.
In the observational study, we used arrival time data from local aftershocks occurring between June 2015 and April 2016 following the M7.8 Gorkha earthquake to determine a 3D Vp velocity structure and hypocenter location in the upper crust of the Main Himalayan Thrust (MHT). Results from the tomographic images show two parallel sub-horizontal low velocity anomalies along profiles perpendicular to the MHT and the velocity contrast is in agreement with surface geological studies.

"TBD"

Eileen Martin, Virginia Tech

"TBD"

Fan-Shi Lin, University of Utah

"TBD"

Jessica Warren, U Delaware

Thesis Defense Seminars

For more information, please contact Julie Lee; julielee@caltech.edu