Spring 2016 Colloquium Schedule:
Matt Tilley and Osazonamen Igbinosun (University of Washington) Research Rotation Presentations
Effects of Repeated M-Dwarf Flaring on the Atmosphere of an Earth-Like Planet in the Habitable Zone
Segura, et al. (2010) showed the electromagnetic radiation from an idealized, single, high magnitude flare from an M-dwarf likely has minimal long-term impact on the atmosphere of an Earth-like planet orbiting in the habitable zone (0.159 AU); calculations including impact of proton flux from a CME, however, indicated dramatic and long-lasting depletion of the ozone column, indicating potential for increased UV flux from further flare activity at the surface of the planet. Extending the previous study, I investigated the effects of repeated flares from an active M-dwarf on an Earth-like planet’s atmosphere and surface conditions using coupled 1D photochemical and climate models. The work includes improved treatments of flare spectral evolution, as well as flare magnitudes and frequency of occurrence motivated by recent observational results from Kepler data analysis for the dM4 flare star GJ 1243. We also investigate and improved treatment of CME produced proton flux into the atmosphere by incorporating a simulated planetary magnetic field from a 3D planetary magnetospheric plasma model. This work is a next step in assessing the potential stellar flare impact on the formation and evolution of life on the surface of an Earth-like planet orbiting an active M-dwarf host.
Screening Plant Growth in Planetary Simulant Soils with Willow/Poplar Endophytes
Particular strains of endophytes (microbes indigenous to plant species) can affect the sustainability of terrestrial plants, particularly hyperaccumulators and transgenics, in iron-rich soils that are compositionally similar to those found on the near surface of Mars. These strains aid growth by reducing plant stress and/or providing nutrients. A hyperaccumulator is a plant capable of growing in soils with very high concentrations of metals; whereas, transgenic plants contain genes which have been artificially inserted. This project monitored hyperaccumulator, transgenic, and commercial crop plants in Mars and lunar simulant over a period of 3 months to determine factors which contributed to growth, such as biomass and root/shoot length.
Laurence Coogan (University of Victoria)
What Controls the Long-Term Carbon Cycle?
The long-term cycling of carbon between rocks and the ocean-atmosphere system on Earth (and perhaps other wet rocky planets) is critical to maintaining a habitable planet. The generally accepted model, dating back to Walker et al. (1981; JGR), is that a negative feedback exists between atmospheric CO2 levels and continental chemical weathering rates and that this acts as a planetary thermostat. However, despite decades of study the link between continental chemical weathering rate and climate have proved difficult to unravel. I will describe an alternative thermostat based on reaction between seawater and the upper oceanic crust. Oceanic crust covers a larger portion of the planet than continental crust, is basaltic in composition making it more reactive than the continental crust and is continually in contact with water. This model will be tested using field observations and geochemical models (e.g. Coogan and Dosso, 2015; EPSL).
Chloe Hart and Matt Koehler (University of Washington) Research Rotation Presentations
The Many Hats of Methanogens: Partners in Syntrophy & a Key to Ancient Nitrogen Fixation
To further “understand the evolutionary mechanisms and environmental limits of life” (Goal 5 in 2008 Roadmap), I plunged into the world of Archaeal biology for my rotation to approach this broad astrobiology objective via two distinct projects. Archaea are similar to Bacteria in shape and size, but are phylogenetically distinct and several inhabit extreme conditions. The first project I pursued involved substrate degradation that is only energetically possible through inter-species interactions. Termed syntrophy, the metabolic interaction requires at least two microbes where one organism is a methanogen, an Archaea, that scavenges hydrogen. I will discuss my attempt to enrich for a syntrophic consortium and the demonstration of syntrophy. The project will lead to a better understanding of mechanisms for inter-species interactions and possibly co-evolution between species. The second project involved a high temperature, nitrogen-fixing methanogen from a hydrothermal vent. Nitrogenase, the enzyme responsible for fixing dinitrogen to the usable form ammonia, most commonly contains an iron-molybdenum cofactor and it’s thought that ancient nitrogenases also used this same combination. It remains unknown if the ancient FS406 reflects this same Mo-based cofactor, a known alternate form, or a completely new type of metal for its nitrogenase to allow it to function at high temperatures. The second goal of my research rotation was to isolate and purify the nitrogenase in the hyperthermophile Methanocaldococcus FS406 in order to characterize the metal cofactor. This research will unearth important information concerning both the origin and evolution of nitrogen fixation.
Exploring the "Bio" in Isotope Biogeochemistry
In most of my work I explore changes in Precambrian life and environment through a geologic perspective, measuring isotope ratios in ancient rocks. After excluding post-depositional alteration, we are often able to infer that the measured values are reflective of primary biologic processes. Attributing a measured value to one, or multiple, biologic processes is dependent on our knowledge of how certain microorganisms affect different isotope ratios. So an essential aspect of isotope biogeochemistry is microbial experiments that determine “fractionation factors” (how isotopes are affected by an organism). I have cultured an organism that grows on thiosulfate, with nitrate as the terminal electron acceptor. Both sulfur and nitrogen isotopes should be fractionated by this reaction, but this fractionation factor is currently unknown. These organisms may have been ecologically important in periods of Earth’s history where oceans had larger concentrations of reduced sulfur species. Are the fractionation factors for sulfur and nitrogen distinct enough to be recognized in the geologic record?
Eric Agol (University of Washington)
What are Little Exoplanets Made Of?
The Kepler spacecraft has enabled the detection of hundreds of transiting exoplanets with small diameters, similar in size to Earth. Only a small fraction of these small planets have masses measured with the Doppler shift method due to the faintness of their stars. I will review recent work in using transit timing to measure the masses of small exoplanets, and discuss what we know about the bulk densities of these planets, and what we speculate their interior compositions to be. These measurements will guide us in the search for potentially habitable, rocky exoplanets.
Aditya Chopra (Australian National University)
The Case for a Gaian Bottleneck: The Biology of Habitability
The prerequisites and ingredients for life seem to be abundantly available in the Universe. However, the Universe does not seem to be teeming with life. The most common explanation for this is a low probability for the emergence of life (an emergence bottleneck), notionally due to the intricacies of the molecular recipe. In this talk, I will present an alternative Gaian bottleneck explanation: If life emerges on a planet, it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. Such a Gaian bottleneck suggests that (i) extinction is the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe and (ii) rocky planets need to be inhabited to remain habitable. In the Gaian bottleneck model, the maintenance of planetary habitability is a property more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the luminosity and distance to the host star.
Roger Buick (University of Washington)
Evolution of Earth’s Nitrogen Cycle: Its Influence on Planetary Habitability
Nitrogen is a major nutrient for all terrestrial life. Life’s distribution, abundance and evolution is thus dependent on the bio-availability of this essential element, but conversely life’s evolution has modified the distribution, speciation and abundance of nitrogen. As a result, the nitrogen cycle has changed markedly through time. In the Hadean and Eoarchean, abiotic fixation would have allowed a very small flux of bio-available nitrogen from the atmosphere, severely limiting the size and diversity of the primordial biosphere. However, efficient biological fixation using Mo-nitrogenase was established by the Mesoarchean, leading to large biomass deposition in marine settings and (possibly) depletion of nitrogen from the atmosphere as a result of enhanced organic burial. During the late Neoarchean in conjunction with the first whiffs of biogenic oxygen to the atmosphere, aerobic nitrogen cycling was temporarily initiated, marked by positive fractionations of nitrogen isotopes indicating active denitrification sending nitrogen gas back to the atmosphere. The Paleoproterozoic “Great Oxidation Event” and subsequent “oxygen overshoot” during the Lomagundi carbon isotopic excursion were marked by widespread aerobic cycling with vigorous denitrification. Towards the end of the Paleoproterozoic and through the Mesoproterozoic, expanded euxinic (sulfidic) conditions in the oceans during the “boring billion” years of environmental stasis caused spatial perturbations in the nitrogen cycle, with aerobic cycling near-shore but anaerobic fixation-dominated cycling offshore. As sulfide strips dissolved copper from seawater, thus removing the key cofactor for the critical enzyme in the last step of denitrification, a nitrous oxide greenhouse may have been operative at this time. It is not clear when the nitrogen cycling attained its modern fully aerobic aspect, but it may have been as late as the Devonian when the deep oceans may have finally become permanently oxidized.
Jonathan Toner (University of Washington)
Liquid Water on Present Day Mars
The occurrence of surface water on present-day Mars is increasingly supported by data from orbiting spacecraft and landed rovers, as well as theoretical studies. Pure liquid water is not stable in the extremely cold and dry surface conditions on Mars; however, concentrated salt solutions can allow liquid water to form. Salt solutions can depress the freezing point of liquid water down to -75°C or lower due to supercooling, and hygroscopic crystalline salts can spontaneously absorb water from the atmosphere to form brine. In this talk, I will explore what evidence currently supports the formation of liquid water on Mars, what the salt composition of that water might be, and the potential for life in such brines.
Jody Deming (University of Washington)
Life in Ice: Informing the Search on other Ocean Worlds
When ice forms on Earth, a liquid phase exists within the ice at temperatures warmer than –55°C if the source fluid is impure. Impurities invariably exist and include both inorganic chemical substances and biological materials, particularly microorganisms, viruses and their organic releases. If the source waters are salty, then the liquid volume fraction of the ice is greater: the temperature-dependent fraction of brine volume in sea ice ranges from ~0.0001 to ~0.2; in glacial ice it rarely exceeds 0.0001; in vitrified glass, it is effectively zero. The extent of the liquid fraction in an ice formation, regardless of source waters or freezing pathway, determines whether the encased organisms are preserved, metabolically active, or reproducing and evolving, assuming other organismal needs and tolerances are also met. Such knowledge from terrestrial studies can inform the search for life on ice-covered moons – in the ice itself and in oceans below an icy crust. Of particular interest is the recovery of microbes that have been preserved in ice, which is a possible scenario to consider for future space missions.
Jan Amend (University of Southern California)
Bioenergetics and Habitability in Hydrothermal Systems and the Subseafloor
Marine sediments are vast biogeochemical reactors that contribute significantly to global element cycles on multiple time scales. Although microorganisms have been found in all deep sediment cores that have been examined, it is not clear how active they are, what reactions they’re catalyzing or how their activities might be altering the long-term diagenesis of marine sediments. To assess the extent to which the physiochemical properties of marine sediments control microbial activity, my collaborators and I combined and quantified global data sets on sedimentation rates, bathymetry, heat conduction, and sediment thickness. The results reveal new estimates for the volume and average thickness of global sediments, the volume of marine sedimentary pore water, and the thermal structure of the marine subsurface. We can also focus more specifically at hydrothermal systems, where seawater mixes with vent fluids, generating steep redox gradients. These can serve as potential energy sources for microbial metabolism, but also for the abiotic synthesis of organic compounds and biomolecules.
David Flannery (Jet Propulsion Lab) has been Cancelled.
Research Rotation Presentations
Arsenic is a powerful redox sensitive element that microbes can exploit for bioenergetic gains. Modern arsenic loaded systems, like the arsenic-rich alkaline Mono Lake, have microbial communities which perform a complete bioenergetic arsenic cycle with a portion of the community capable of autotrophic oxidation of As(III) and another portion of the community performing dissimilatory heterotrophic reduction of As(V). It has been hypothesized that microorganisms had the capacity to metabolize arsenic as much as 3.4 billion years ago, with recent fossil evidence indicating an active microbial arsenic cycle in 2.72 billion year old fossilized stromatolites. For my research rotation, I worked with Roger Buick and Eva Stüeken to investigate bulk arsenic concentrations collected from marine sedimentary shales through geologic time, dating back to the early Archaean. These marine shales are a depositional time log recording the flux of various elements through the marine system over time. Marine shale arsenic composition can help elucidate the environmental arsenic conditions that existed in the early anoxic oceans with a more direct quantitative measure.
Missed the last seminar series? See our archive for abstracts and video recordings of all past talks from 2003 - present.