May 30, 2013: New ideas about the origin of the Earth and Moon
In the standard model, Earth accreted via a series of giant impacts and the last giant impact produced the Moon and fully melted the Earth. The Moon and Earth are identical in multiple isotope systems that show significant variations between most meteorite groups and planetary bodies. Thus, the simplest explanation for the isotopic similarity is that the Moon and Earth’s mantle have a common origin. However, the canonical giant impact model predicts that the Moon is primarily composed of material from the impactor, which should have had a different isotopic signature than Earth. In...
Read MoreMay 23, 2013: The Origin of Solar and Extrasolar Planets
The modern wealth of data on extrasolar planets is a boon to theoretical studies of the origin and evolution of planetary systems. However the great diversity of exoplanet systems also poses challenges to the goal of a coherent, unified theory of planet formation. This talk will present dynamical models of the most crucial stages of planet growth. First I will address the origin of the solid building blocks known as planetesimals. Aerodynamic processes, highlighted by the streaming instability, play a crucial role in the emergence of planetesimals within turbulent gas disks. Such models of...
Read MoreMay 21, 2013: Puzzles in Giant Planet Formation
Despite the many hundreds of known “giant” exoplanets, theoretical models still struggle to form them. Under the core-accretion, gas-capture model of giant planet formation, it is still challenging to explain how the required ~10 Earth mass rocky/icy cores can form within the lifetime of their host gaseous circumstellar disks. In this talk I will present two different new lines of research to address this timescale dilemma. I will explore whether or not a newly identified, extremely fast aerodynamic aided accretion of “pebbles” may present a mechanism to form...
Read MoreMay 24, 2013: Deltaic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars
A fundamental long-standing question regarding Mars history is whether the flat and low-lying northern plains ever hosted an ocean. The best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy. Here we use high-resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the Aeolis Dorsa region, just north of the dichotomy boundary. Observations of stacked channel bodies, switches in channel direction tied to a single node, and stratal geometries indicate that...
Read MoreMay 16, 2013: The Beginning of Life and the End of Solar Systems
I will address several questions related to how much life there might be in our Galaxy: What affects whether potentially Earth-like exoplanets might be good abodes for life? What kind of (Milankovitch-like) variations in habitability might be expected in exosolar systems? And what does the origin of life on Earth tell us about the probability of life elsewhere in the Galaxy? I will also discuss the longterm evolution of binary systems, including thermal and chemical changes, and orbital evolution. In particular, Jupiter will eventually become a hot Jupiter, and if it were somewhat closer to...
Read MoreApril 26, 2012: Precise Assemblies, Clusters, Superatoms, and Cluster-Assembled Materials
Precise clusters offer a new set of building blocks with unique properties that can be leveraged both individually and in materials in which their coupling can be controlled by choice of linker, dimensionality, and structure. Initial measurements in both of these worlds have been made. Isolated adsorbed or tethered clusters are probed with low-temperature scanning tunneling microscopy and spectroscopy. Even closely related elements behave differently on identical substrates. Surprising spectral variations are found for repeated measurements of single isolated, tethered clusters. In periodic...
Read MoreApril 19, 2012: Recent Insights into Planet Formation and Debris Disks
I will discuss recent insights that we have gained into planet formation and debris disks. In the first half of my talk, I will focus on the Kuiper belt, located at the outskirts of our planetary system, and the formation of debris disks. I will show how studying small km-sized Kuiper belt objects enables us to put our Kuiper belt into context of debris disks around other stars and I will explain how we can use the size distribution of small Kuiper belt objects and debris disks to gain insights into collisional cascades and the material properties of the objects themselves. In the second...
Read MoreApril 5, 2012: The Earliest Aqueous, Habitable(?) Environments on Mars: A View from Orbit
The emerging picture of Mars’ first billion years includes diverse environments involving liquid water and chemical alteration. Clay, carbonate, chloride, and sulfate minerals have all been detected and mapped from orbit in coherent geologic units. When near-infrared spectroscopic detections of minerals from the orbiting CRISM imaging spectrometer are coupled with high-resolution images of morphology provided by orbiting cameras, distinctive aqueous, potentially habitable, environments can be identified, preserved in the geologic record. I will give a global overview of the most recent...
Read MoreJanuary 19, 2012: The Bucaramanga Nest: A Natural Lab for Understanding the Physics of Intermediate-depth Earthquakes
The physical mechanism of intermediate-depth earthquakes is still under debate. In contrast to conditions in the crust and shallow lithosphere, at temperatures and pressures corresponding to depths >50 km one would expect rocks to yield by creep or flow and not by brittle failure, so there has to be a physical mechanism that allows for brittle or brittle-like failure for intermediate-depth earthquakes. Two such mechanisms have been proposed: dehydration embrittlement and thermal shear runaway. Earthquake nests represent a region with high earthquake concentration that is isolated from...
Read MoreJanuary 26, 2012: Is the Earth normal?
Knowing that extrasolar planetary systems are common, we would like to learn whether the Earth is normal or distinctive. Bulk Earth is 94% composed of O, Mg, Si and Fe and very deficient compared to the Sun in volatiles such as C and N. With our recent observations of white dwarf stars that have recently accreted tidally-disrupted minor planets that are about 300 km in diameter, we find a similar compositional pattern in extrasolar asteroids. While there must be individual exceptions, in aggregate, the studied extrasolar asteroids also are as “dry”; they probably formed interior...
Read MoreFebruary 2, 2012: Mapping the Amorphous-to-Crystalline Transitions in CaCO3 Biominerals
Mapping the Amorphous-to-crystalline transitions in CaCO3 biominerals with 20-nm resolution One of the most fascinating aspects of calcite biominerals is their intricate and curved morphology, quite different from the rhombohedral crystal habit of geologic calcite. These morphologies, as well as space-filling and greater resistance to fracture, are achieved via amorphous precursor mineral phases (1). In this talk we will show that in sea urchin larval spicules two distinct phase transitions occur, 12 and 23 (2). Both transitions are regulated by inhibiting proteins, which introduce...
Read MoreFebruary 9, 2012: An overview of fusion energy research: taming turbulence and transport in magnetized plasmas
I will give an overview of the challenges associated with harnessing nuclear fusion as a terrestrial power source and the progress that has been made in research in this area. In particular, I will discuss turbulence in magnetically-confined plasmas and how transport associated with this turbulence limits the confinement achievable in current and planned experiments. I will present recent UCLA research that has helped advance our understanding of the basic physics of turbulence and turbulent transport in magnetized plasmas.
Read MoreFebruary 23, 2012: Towards inferring fault rheological properties and predicting future earthquake patterns from seismographs
Study of the earthquake source brings about a set of fascinating interdisciplinary problems characterized by nonlinearity, a broad range of spatial and temporal scales, rare but catastrophic events, competing physical mechanisms, remote observations, inverse problems, non-uniqueness, and substantial societal significance. The ultimate challenge is to understand and quantify factors controlling the spatio-temporal behavior of active faults, including earthquake nucleation, seismic patterns, and the interaction of seismic and aseismic fault slip. My research aims to address this challenge by...
Read MoreMarch 1, 2012: Europa’s Great Lakes
With an icy exterior covering a global ocean, Europa has long been a target of interest in the search for life beyond Earth. Europa exists in a dynamic environment, subject to intense irradiation and impact as well as immense tides from Jupiter. These processes deliver important thermal and chemical energy that could be critical to supporting a putative biosphere. In the past few decades the debate about habitability of Europa has been focused strongly on the thickness of the ice shell. However, an arguably more critical question is: how does the ice shell recycle? New analysis of...
Read MoreMarch 8, 2012: Ingassing, Storage and Outgassing of Terrestrial Carbon through Geologic Time
The Earth is unique among the terrestrial planets in our solar system in having a fluid envelope that fosters life. The key behind Earth’s habitable climate is well-tuned cycles of carbon (C) and other volatiles. While on ten to thousands of year time-scales the chemistry of fluids in the atmosphere, hydrosphere, and biosphere is dictated by fluxes of carbon between the near surface reservoirs, over million to billion years this is maintained by chemical interactions of carbon between the Earth’s interior, more specifically the Earth’s mantle, and the exosphere. This is because of the...
Read MoreSeptember 22, 2011: At the Edges of the Solar System
The small bodies of the Solar System have a story to tell about the history of our Solar System. Near Earth Objects — asteroids whose orbits bring them near the Earth’s orbit — are interesting both because they sample compositions from throughout the Solar System and because they can, and do, hit the Earth. Kuiper Belt Objects, at the outer edge of the Solar System, are, in contrast, relatively primordial and record the formation environment in the early Solar System. In my talk, I will present our latest results in studies of both Near Earth Objects and Kuiper Belt Objects,...
Read MoreSeptember 29, 2011: Physical Processes and Evolutionary Consequences
Three vignettes of different scales of flow and landscape influence on biotic process will be presented. 1) The Late Precambrian Rangeomorph fauna of Mistaken Point Newfoundland constitute the earliest community of large multicellular organisms. Through flow modeling we demonstrate that these organisms evolved large size to access higher velocities in a low flow environment. Access to velocity overcomes diffusional limits to resource acquisition in a community dependant on dissolved resources, providing the impetus to the evolution of large multicellular form. 2) Rapid landscape evolution of...
Read MoreOctober 6, 2011: Megafloods
Megafloods (terrestrial water flows with discharges exceeding one million cubic meters per second) are the largest known freshwater floods, with flows comparable in scale to (though of shorter duration than) ocean currents. Although there are no modern examples of megafloods, such flows occurred during major periods of Earth’s glaciation and during past epochs on Mars. A prominent example is the paleoflooding caused by late Pleistocene outbursts from Glacial Lake Missoula, which formed when the Purcell Lobe of the Cordilleran Ice Sheet extended south from British Columbia to the basin...
Read MoreOctober 13, 2011: Thinking and Learning in the Geosciences
This colloquium is intended as an introduction to research on thinking and learning in the Geosciences, pitched for an audience who know a lot about geosciences and not so much about education research. As geoscientists, we ask our brains to make sense of an object larger than the human senses can encompass at one time, older than any time span with which humans have direct experience, which is not susceptible to experimental manipulation, whose crust at any given point has experienced superimposed chemical, physical and biological events, where flows of matter and energy intertwine at a...
Read MoreOctober 20, 2011: The Electrochemical Earth
s the Earth an active fuel cell? Or is it corroding? This talk shows how electrochemical processes on Earth and planets may create a wide range of physical and chemical effects. Experiments and theory suggest that geo-electrochemical processes may generate specific isotope signatures describing electrochemical disequilibrium.
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