EPSS Colloquium - spring-2018
Chemical and Dynamical Evolution of Dust in the Solar Nebula
April 3, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Fred Ciesla - University of Chicago
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The early stages of planet formation involve the coagulation of sub-micron dust that was suspended in the solar nebula into larger aggregates, which themselves come together to form the building blocks of the planets. During this stage of growth, dust grains and the bodies in which they are contained are subjected to a number of dynamical processes which caused them to migrate significant distances from where they first formed. Evidence for this redistribution is readily found in the meteorite record, with chondritic meteorites made of individual components that record very different formation conditions. This transport will expose dust grains to a variety of environments which will drive chemical and physical evolution of the dust grains. I will present results which allow us to begin understanding the feedbacks between dynamical and chemical evolution within the solar nebula, and how these effects may be seen in the meteorite record as well as planet-forming disks around other stars.
Twenty-Five years of SIMS at UCLA
April 10, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Kevin Mckeegan - UCLA
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On March 24, 1993, the Dept. of Earth & Space Sciences held a party attended by the head of the NSF’s Instrumentation & Facilities Program for Earth Sciences, the Vice Chancellor for Research, board members of the W.M. Keck Foundation, the president/principal owner of CAMECA, as well as ESS and IGPP faculty & staff. The occasion for celebration was the opening of the W.M. Keck Foundation Center for Isotope Geochemistry with its centerpiece the CAMECA ims 1270, the northern hemisphere’s first high-sensitivity, high-resolution ion microprobe (or secondary ion mass spectrometer, SIMS). Speeches were made, toasts given, and a demonstration performed (not without some problems, as it turned out). Following an intensive multi-year period of instrument and technique development, the laboratory was commissioned as a National Facility under the direction of Prof. T. Mark Harrison along with co-I’s Prof. Mary Reid and laboratory manager, Specialist Kevin McKeegan. Our intention, as articulated in that and eight subsequent NSF proposals, was “to create a world-class facility for in situ microscale isotopic analyses of geologic materials and to provide access to its unique capabilities to the broader community to address important problems in earth and planetary science.” Now with a perspective of 25 years, I will present some of the challenges and benefits of running a National Facility and highlight several significant accomplishments of the UCLA Keck lab in addressing a wide range of problems in geochronology, geochemistry, and cosmochemistry. The potential of the new $5M ion microprobe, the UCLA/CAMECA ims 1290, for enabling further advancements in high resolution studies of planetary materials will also be discussed.
Debris Flows Following Wildfire in the Western U.S.
April 17, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Paul Santi -
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The frequency, intensity, and areal extent of wildfires in the Western United States are increasing. Changes imposed on watersheds during and after burning result in a dramatic increase in debris-flow occurrence and magnitude, which in turn poses risks to human life and property, especially as the urban-wildland interface advances into mountainous areas. Flows can be initiated following wildfire by low intensity rainfall events, and they grow substantially in volume through channel scour while in transit. On average, flow volumes are 3-5 times larger immediately after wildfires, and the volume magnification effects linger for 1-3 years before the watershed recovers. Volume is difficult to predict accurately, but it can be estimated using multiple linear regression models that rely on GIS-friendly inputs such as area burned, rainfall totals, and watershed slope characteristics. A new probabilistic model has been shown to be more accurate and it relies on even fewer terms. Discharge rates and velocity are also difficult to predict, so reasonable ranges are derived using databases of previous field measurements. Damming and avulsion of the flows make runout patterns unpredictable, but recent studies have helped to quantify the process.
The Birth Environment of the Solar System
April 24, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Ed Young - UCLA
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The relative abundances of the radionuclides in the solar system at the time of its birth are crucial arbiters for competing hypotheses regarding the birth environment of the sun. The presence of short-lived radionuclides, as evidenced by their decay products in meteorites, has been used to suggest that particular, sometimes exotic, stellar sources were proximal to the sun's birth environment. The recent confirmation of neutron star - neutron star (NS-NS) mergers and associated kilonovae as potentially dominant sources of r-process nuclides can be tested in the case of the solar birth environment using the relative abundances of the longer-lived nuclides. Critical analysis of the 15 radionuclides and their stable partners for which abundances and production ratios are well known suggests that the sun formed in a typical massive star-forming region (SFR). The apparent overabundances of short-lived radionuclides (e.g., 26Al, 41CA, 36Cl) in the early solar system appears to be an artifact of a heretofore under-appreciation for the important influences of enrichment by Wolf-Rayet winds in SFRs. The long-lived nuclides (e.g., 238U, 244Pu, 247Cr, 129I) are consistent with an average time interval between production events of 108 years, seemingly too short to be the products of NS-NS mergers alone. The relative abundances of all of these nuclides can be explained by their mean decay lifetimes and an average residence time in the ISM of ~ 200 Myr. This residence time evidenced by the radionuclides is consistent with the average lifetime of dust in the ISM and the timescale for converting molecular cloud mass to stars.
A Little Rough Around the Edges
May 1, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Brett Gladman - University of British Columbia
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Our understanding of the processes of planet formation have evolved considerably in the last 20 years as they have exposed that many planetary systems in our Galaxy do not look like our own. In particular, the inner and outer edges of our planetary disk come into focus and raise several interesting questions. Where was the outer edge of condensing solids in our outer Solar System? Our Kuiper Belt yields clues, but provides only unclear hints as to the answer. Why do we not have more massive planets close to our star, as many planetary systems do? I suggest that we may have in the past, and that Mercury is a collisional relic of an epoch where we had other planetary bodies interior to Venus.
Data-Driven Discovery and the Co-Evolution of the Geosphere and Biosphere
May 8, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Bob Hazen - Carnegie Institution for Science
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A fundamental goal of the geological sciences is the deep understanding of planetary evolution. Recent research employing large and growing data resources in mineralogy, petrology, paleobiology, paleotectonics, geochemistry, and proteomics underscores the intertwined influences of life and rocks on Earth’s evolution. We therefore are exploring data science approaches to longstanding problems in geology. Data-driven discovery depends on three key developments: (1) enhanced data resources in diverse geo- and bio-related fields; (2) development and implementation of powerful analytical and visualization methods; and (3) creative framing of questions related to the evolving geosphere and biosphere in space and time. We are especially interested in visualization methods that illustrate multiple attributes of complex systems. In particular, network analysis provides a dynamic, quantitative, and predictive visualization framework for employing data to explore complex and otherwise hidden higher-dimensional patterns of diversity and distribution in mineralogy, paleobiology, and protein structures. Network analysis (see figures) facilitates quantitative comparison of coexistence patterns simultaneously among hundreds of mineral or fossil species and their localities, exploration of varied paragenetic modes of mineral groups, investigation of changing patterns of mineral and fossil occurrence through deep time, and comparisons of lithologies from different planets and moons. Network analysis, furthermore, represents an effective visual approach to teaching and learning in Earth and planetary sciences.
A Limit on Earth’s Topography Revealed by Channel Steepness in Tropical Granitic Landscapes
May 15, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- George Hilley -
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Rivers determine the maximum elevation of most tectonically active mountain belts, control the coupling between climate and tectonic processes, and archive the pace and tempo of fault-related rock uplift rates. Long-profiles of rivers in steep, non-glaciated landscapes are thought to be controlled by the bedrock incision rate, leading many to posit that channel discharge and slope determine the pace of river incision (hereafter referred to as the power-law incision rule). We tested the power-law incision rule in watersheds varying by four orders of magnitude in erosion rate (4.7 x 10-3 - 7.1 mm/yr mm/yr), and combined these with a global analysis of erosion rates and topography. Our data and analyses reveal that this rule breaks down in steep, rapidly eroding landscapes, in which river profiles reach a threshold steepness that is invariant in steep watersheds. This limit to the steepness of channels suggests the present and past overall topographic relief on Earth may be limited by the horizontal extent of active rock uplift, with higher relief resulting from longer channels of a given steepness, rather than the rate of uplift itself.
Experimental Investigation of Core Crystallization in Small Terrestrial Bodies
May 22, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Anne Pommier -
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Core crystallization is a crucial ingredient in the evolution of terrestrial bodies and is controlled primarily by chemistry and temperature. Crystallization within a metallic core releases latent heat and gravitational energy, influencing significantly the processes responsible for the presence of a magnetic field. The diversity of magnetic fields observed in small terrestrial bodies, such as Mars, Mercury or Ganymede suggests different core cooling history. Past missions have observed that Mars does not currently possess an internally-generated magnetic field but likely had one early in its history, while Mercury currently possesses a weak magnetic field and Ganymede is characterized by a strong one. The origin of this diversity is not well understood and seems to depend highly on the onset, depth, and rate of crystallization. This presentation will focus on the effect of chemistry on core crystallization and its implications for the magnetic field. Phase equilibria and electrical experiments on core and core-mantle analogues have been conducted in the Fe, Fe-S, Fe-S-O and Fe-S-Si (+/- olivine) systems using the multi-anvil apparatus at conditions relevant to the core of small terrestrial bodies (pressure up to 20 GPa and temperature up to 1850°C). The effect of sulfur and oxygen on core crystallization from melting relations will be discussed in terms of light element distribution and core compositional stratification. Laboratory-based electrical resistivity-crystallization models will be used to provide insight regarding the insulating properties of chemical heterogeneities that result from core crystallization or mantle-core interactions. All results will be compared to the magnetic history and available observational constraints on the core structure, temperature and composition of Mars, Mercury and Ganymede.
Reservoirs of Carbon and Water and Environmental Change on Early Mars
May 29, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Bethany Ehlmann - California Institute of Technology
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The last decade of landed and orbital exploration reveals abundant hydrated silicate minerals and rarer carbonate minerals that are the signs of water-rock interaction during more habitable periods during Mars early history. I will provide an overview of the geology of some of the most significant sites recording this history and discuss implications for reservoirs of volatile elements on Mars and their cycling.
Stowaways: Using shipwreck microbiomes to study spill impacts and dispersal in in the deep-sea
June 5, 2018
3:30 p.m. - 4:30 p.m.
Geology 3656
Presented By:
- Leila Hamdan -
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There are ~2,000 historic shipwrecks in the Gulf of Mexico spanning 500 years of history. Shipwrecks become artificial reefs and islands of biological diversity. Residues from the Deepwater Horizon Spill were deposited on the seafloor in areas where historic shipwrecks are present. The spill creates potential for contact of oil with shipwreck remains and the biological communities on and around them. These interactions may impact the preservation of historic shipwrecks. Accordingly, this study examined the spill’s lasting effects on microbiomes surrounding 7 historic shipwrecks. The study included steel-hulled World War II-era and wooden-hulled 19th century shipwrecks. Through comparative analysis of 16S rRNA sequence libraries from wrecks located within and external to the spill’s seafloor footprint, this study documented that the German U-boat U-166 and the sailing vessel known as Mardi Gras were exposed to deposited oil. The work also provided opportunity to examine the effect that shipwrecks have on microbiome diversity. A shipwreck may be an oasis for diversity, and assist transport of microorganisms across the seafloor. Sediment cores were collected along 200 m transects at 2, and 25 m intervals away from the wrecks, using Jason-style push corers or an instrumented MC800 deep-sea multicorer. Shannon diversity and species richness were highest near the shipwrecks, and declined as a function of distance. Bray-Curtis similarity revealed that community composition was distinct in samples near the wrecks vs. away from them. Communities were organized by distance, and secondarily by depth. This study indicates that deep-sea microbiomes are shaped by shipwreck ‘island habitats’.