Welcome to the 2017 Fall Astrobiology Colloquium Series!
|Date||Speaker||Title of Talk|
Georgia Institute of Technology
|Title: The Environmental Context of Early Animal Evolution|
University of Colorado, Boulder
|11/14/2017||Lucas Mix||Title: Astrrobiology and Human Significance|
Jet Propulsion Laboratory
Title: Geophysical investigations of habitability in ice-covered ocean worlds
Abstract: Geophysical measurements can reveal the structure of icy ocean worlds, including the trans- port of volatiles. The inferred interior density, temper ature, sound speed, and electrical con- ductivity thus characterize their habitability. We explore the variability and correlation of these parameters using 1D internal structure models and available constraints on the ther- modynamics of aqueous MgSO4, NaCl (as seawater), and NH3; pure water ice phases I, II, III, V, VI; silicates; and any metallic core that may be present. We identify limits in the ther- modynamic data that narrow the parameter space that can be explored: insufficient coverage in pressure, temperature, and composition for end-member salinities of MgSO4 and NaCl, and for relevant water ices; and a dearth of suitable data for aqueous mixtures of Na-Mg-Cl- SO4-NH3. For Europa, ocean compositions that are oxidized and dominated by MgSO4, vs reduced (NaCl), illustrate these gaps, but also show the potential for diagnostic and measur- able combinations of geophysical parameters. The low-density rocky core of Enceladus may comprise hydrated minerals or anhydrous minerals with high porosity. Titan’s ocean must be dense; thin ice and high salinity imply high heat flux. Titan may have little or no high- pressure ice. Ganymede’s silicious interior is deepest among all known ocean worlds, and may contain multiple phases of high-pressure ice, which will become buoyant if the ocean is sufficiently salty. Eutectic oceans cannot be adequately modeled using available thermo- dynamic data. Callisto may also lack high-pressure ices, but this cannot be confirmed due to uncertainty in its moment of inertia.
Title: Reconstructive biology as a window into historic biochemical optima
Abstract: Two datasets, the geologic record and the genetic content of extant organisms, provide complementary insights into the history of how key molecular components have shaped or driven global environmental and macroevolutionary trends. Changes in global physicochemical modes over time are thought to be a consistent feature of this relationship between Earth and life, as life is thought to have been optimizing protein functions for the entirety of its ~3.8 billion years of history on Earth. Organismal survival depends on how well critical genetic and metabolic components can adapt to their environments, reflecting an ability to optimize efficiently to changing conditions. The geologic record provides an array of biologically-independent indicators of macroscale atmospheric and oceanic composition, but provides little in the way of the exact behavior of the molecular components that influenced the compositions of these reservoirs. By reconstructing sequences of proteins that might have been present in ancient organisms, we can downselect to a subset of possible sequences that may have been optimized to these ancient environmental conditions. How can one use modern life to reconstruct ancestral behaviors? Configurations of ancient sequences can be inferred from the diversity of extant sequences, and then resurrected in the lab or in modern host organisms to ascertain their biochemical attributes. Here I present a novel approach, where the focus of the study is not just the sequence diversity of past proteins but the diversity and evolution of protein functionality. This functionality is evaluated in the context of geology's convoluted record of a multiplicity of enzyme functions acting upon environmental reservoirs over time. Studying the interface of past molecular behavior and environmental conditions may yield new insights into the interpretation of deep time biosignatures, as expressed by the impact of organismal optima on metabolites and fossil remains.
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