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EPSS Colloquium - fall-2014

Space, energy, time: a closer look at minerals at extreme conditions

Oct. 2, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Wendy Mao - Stanford
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Experimental technology has come a long way in terms of our ability to reach high pressures and temperatures. Using static and dynamic compression techniques we can now cover the wide range of conditions found within our planet. Concurrently, we rely on a suite of in-situ probes to characterize materials behavior at these extreme conditions where we are pushing the envelope in terms of spatial, energy, and temporal resolution. I present a few examples which demonstrate the power of new x-ray tools for looking at Earth materials at extreme conditions.

Hunting for Killer Asteroids, the Past, Present and Future of Near-Earth Asteroid Surveys

Oct. 9, 2014
6:30 p.m. - 7:30 p.m.
Geology 3656

Presented By:

  • Alan Harris - UCLA Alumnus
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The prospect of cosmic bodies impacting the Earth was realized even by Edmund Halley, who first mapped the orbit of an object crossing the orbit of the Earth’s, the comet that now bears his name. More recently, the risk from cosmic impact was brought home by the Tunguska impact of 1908 in Siberia, the realization that it was an impact that led to the extinction of the dinosaurs, and more recently, the first-hand observation of the impacts of comet Shoemaker-Levy 9 on Jupiter twenty years ago, and just last year by the bolide that exploded close to Chelyabinsk, Russia, causing significant damage and injuries, but fortunately no deaths. In this lecture, I will trace the history of our recognition of this most rare, but potentially most damaging, natural hazard and put it in context with other natural hazards such as earthquakes, volcanoes, floods, and so forth. I’ll trace the history and progress of efforts to find and catalog Near-Earth Asteroids, and thereby “retire” that fraction of the risk, at least for the short term over which we can be sure they will not collide with the Earth. Currently, surveys have “retired” more than 90% of the intrinsic risk, having found none of the discovered objects to be on a course of high probability of impact for at least the next 50 years. Future surveys hold the prospect of “retiring” another order of magnitude of the remaining risk. It should come as no surprise that a subject as provocative as this one, which does have the potential for “end of the world” scenarios, brings out junk science claims, inflated media attention, and yes, claims of apocalypse. I’ll close with a brief romp through some of the more egregious examples, and suggest some things we should not do about the impact threat.

Neotectonics of the East African Rift System

Oct. 16, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Sarah Stamps - UCLA
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The Nubian and Somalian plates actively diverge along the topographically high, ~5000 km long East African Rift System (EARS). As no major subduction zones bound Africa, one can assume that the forces driving the Nubia-Somalia plate system result primarily from boundary forces (due to mantle buoyancies and resistance along faults) and lateral variations in lithospheric gravitational potential energy. Images from seismic tomography and convection models suggest active mantle flow beneath Africa. However, the contribution from large-scale convection to the force balance driving plate divergence across the EARS remains in question. In this work we investigate the impact of mantle shear tractions on the dynamics of Nubia-Somalia divergence across the EARS using both top-down and bottom-up modeling approaches. Results from both techniques indicate a large contribution from mantle tractions is not required to explain present-day Nubia-Somalia divergence. This work suggests lithospheric buoyancy forces overcome mantle resistance and dominate the force-balance driving present-day rifting along the EARS. We also compare lithospheric strength estimates with calculated tectonic stress and find lithospheric weakening is required to initiate rupture, but once rifting has begun gradients in gravitational potential energy are sufficient to sustain continental rifting.

The transient gravity field of an earthquake

Oct. 23, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Jean-Paul Ampuero - Caltech
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Earthquakes generate transient and static deformations that redistribute mass and induce instantaneous and long-ranged changes in the Earth's gravitational field. In particular, the volumetric deformation carried by seismic P waves induces remote gravity perturbations even at distances beyond the P wave front. If practically measurable, these "prompt gravity perturbations"expected between the onset time of the rupture and the arrival time of seismic waves would add a new dimension to real-time seismology that may enhance earthquake and tsunami early warning capabilities. I will present theoretical results that characterise the structure and amplitude of prompt gravity perturbations. Based on this, I will argue that prompt gravity signals should be observable by next-generation high-precision gravity-strain meters.

When did the terrestrial biosphere become important to global biogeochemistry

Oct. 30, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Nathan Sheldon - University of Michigan
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The overwhelming majority of phosphorus in the oceans today is derived from continental weathering and delivered via rivers to shallow shelf areas. Areas with high phosphorus fluxes are typically characterized by high marine productivity and areas with low fluxes are often nutrient limited. When and how was this pattern established? Three competing hypotheses include: 1) the pattern was established early, with the first emergence of significant continental land masses in the Archean, 2) the pattern was established late, with the rise of both vascular and non-vascular land plants in the Silurian, or 3) the pattern was established in the Proterozoic, perhaps coincident with either biological evolution or plate tectonic changes such as the assembly of Rodinia. To evaluate each of these competing hypotheses, records of carbon and phosphorus in marine and terrestrial reservoirs have been compiled. Using bedrock-parented paleosols (fossil soils) to evaluate phosphorus weathering, while phosphorus may be leached or retained during the Archean and Paleoproterozoic, after ca. 1.8 Ga paleosols are similar to modern soils in that they retain phosphorus quantitatively and even may show (bio-) accumulation at the tops of profiles. There is no change in the phosphorus content of the continents being weathered, so it is most likely that the change was triggered by a change in weathering intensity. Similarly, evidence for "modern style" soil carbon dynamics indicates that relatively deep carbon cycling was established no later than 1.1 Ga. The timing of both of these shifts precludes either an Archean or Ordovician establishment of modern biogeochemical nutrient cycles. Clear shifts in carbon and phosphorus biogeochemical cycles are recorded by marine rocks by 850 Ma. The discrepancy in the timing of the terrestrial and marine shifts suggests that a tectonic control on the amount of emergent land mass may have driven our recognition of the establishment of modern-style biogeochemistry

Little creatures with major impacts: How microbes control biogeochemical cycles in the ocean

Nov. 6, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Tina Treude - UCLA
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Microbes have established major biogeochemical cycles on our planet and still govern most of our cycles today. Although tiny and inconspicuous, microbes are the most amazing creatures when it comes to metabolism. Some of them even gain energy with the use of solid metals. In this presentation I will provide a general overview of geomicrobiological processes, how microbes "breathe", how they interact with their environment, and how we can measure their activity. More specifically, I will give examples of my past and current geomicrobiological studies in marine systems including, e.g., methane seeps and interactions of microbes with minerals. With this seminar I would like to say "Hello" to EPSS and AOS and to provide you an insight into my current and future research topics. I hope you enjoy it.

The Composition of Vesta: What we are learning about the Smallest Terrestrial Planet

Nov. 13, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Eleonora Ammanito - UCLA
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During its year of operations at Vesta, Dawn acquired high quality spectra from 0.2 to 5 microns in the 864 spectral channels of the Visible and Infrared Mapping Spectrometer (VIR). These data were used to characterize and map the distribution of minerals on Vesta. VIR spectra are dominated by pyroxene absorptions at 0.9 and 1.9/µm indicating the ubiquitous presence of this family of minerals on the surface and confirming the hypothesis that Vesta is a differentiated body. Since olivine is a major component of the mantles of differentiated bodies, much effort has been dedicated to the identification of the possible presence of olivine on Vesta’s surface especially within Rheasilvia basin in the South Pole where, according to numerical models, the impact(s) could have exposed the mantle. While in the southern regions there is so far no evidence of olivine, it has been detected mainly in the northern hemisphere. The identification of olivine-rich lithologies on Vesta can constrain different petrologic scenarios, each of which predicts different abundances and distributions of olivine. The compositional context of the olivine sites suggests a mantle source, where the geographical location jeopardizes this conclusion. Thus while the early Dawn observations concluded that Vesta was similar to predictions, our later compositional analysis suggests a complex evolutionary history for Vesta not adequately described by the current models.

The Babylonian eggs: celebrating Galileo’s 450th birthday

Nov. 20, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Claudio Pellegrini - Stanford
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To celebrate the 450th anniversary of Galileo’s birthday, he was born in Pisa in 1564, I want to talk of celestial objects - stars, comets, satellites - that he discovered and studied, their role in his scientific career, the fights against the Aristotelian philosophers and the theologians. I will also comment on Galileo’s pen, his literary ability and his cutting sarcasm, that he used to defend and advance his ideas.

Tectonics

Dec. 6, 2014
4 p.m. - 5 p.m.
Geology 3656

Presented By:

  • Roland Burgmann - Berkeley
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Seminar Description coming soon.