Exotic Biochemistries on Saturn's Moon Titan and Beyond
October 03, 2014 12:00p - 2:30p
No abstract available.
October 03, 2014 12:00p - 2:30p
No abstract available.
April 04, 2014 12:00p - 2:30p
Blood Falls is an iron-rich, saline feature at the terminus of Taylor Glacier in the McMurdo Dry Valleys, Antarctica. Geophysical and geochemical data indicate that the source of this surface outflow originates below the glacier, however the extent of the subglacial brine remains unknown. The brine harbors a microbial community that persists, despite cold, dark isolation. In order to better understand this ecosystem, drilling into the subglacial source will be required. Antarctic subglacial environments, like astrobiological targets on extraterrestrial worlds, are pristine ecosystems that warrant protection. Modern ice drilling projects, such as those planned for Blood Falls, are developing clean access approaches to prevent the contamination of both the subglacial environment and the samples retrieved. In this talk I will highlight recent expeditions to Blood Falls, which collectively shape our current understanding of the Taylor Glacier ecosystem. The brine below Taylor Glacier is an example of the diversity of potential microbial habitats hidden beneath Antarctic ice and provides important insight into subice microbial community structure and function. Collaborative, interdisciplinary studies of Blood Falls, such as those presented here, will enable the development of relevant tools for geomicrobiological examination of other subglacial environments on Earth and help prepare us for the exploration of icy extraterrestrial targets.
March 07, 2014 12:00p - 2:30p
NASA's Cassini mission has revealed Saturn's larger moon Titan to be a world rich in the "stuff of life." Reactions occurring in its dense nitrogen-methane atmosphere produce a wide variety of organic molecules, which subsequently rain down onto its surface. If these molecules mix with water found in cryovolanic lavas or impact melts on Titan's surface, they may react to form biological molecules such as amino acids. In this presentation, I will report on experimental work seeking to determine the type and quantity of biomolecules formed under conditions analogous to those found in transient liquid water environments on Titan. These reactions are intriguingly similar to reactions that may have occurred on the early Earth, and provide clues to the origin of life on our own world and worlds throughout the universe.
February 07, 2014 12:00p - 2:30p
The Wide Field Camera 3 (WFC3) on HST provides the opportunity for spectroscopic characterization of molecular features in transiting exoplanet atmospheres, a capability that has not existed in space since the demise of NICMOS on HST and the IRS on Spitzer. WFC3's slitless grism design and the stable and reliable pointing and thermal environment of HST provide an excellent platform for high-precision spectroscopic monitoring of transiting exoplanet host stars. Additionally, the wavelength range of WFC3's long-wavelength grism covers several molecular absorption bands which are relevant to planetary atmospheres, most notably the 1.4 micron water band. I will present analysis of WFC3 transit and eclipse measurements for a number of highly irradiated, Jupiter-mass planets observed over several HST cycles, with a focus on confirming which planets exhibit water absorption in transit and/or eclipse and measuring the characteristic brightness temperature at these wavelengths. Measurements of molecular absorption in the atmospheres of these planets offer the chance to explore several outstanding questions regarding the atmospheric structure and composition of hot Jupiters, including the possibility of bulk compositional variations between planets and the presence or absence of a stratospheric temperature inversion, and I will describe our progress and plans towards resolving some of these questions.
December 06, 2013 12:00p - 2:30p
Humans evolved and developed, and are born and raised, in a 1g gravity field. In some sense we have no business being in space where there is “zero gravity” (more accurately, freefall or microgravity). This presentation will discuss some of the ways in which the body adjusts to the extreme environment of spaceflight, and some of the ways in which this adjustment is insufficient and what researchers are doing about it. These physiological issues will become more serious as preparations are made for long-duration flights to asteroids, the moon, or Mars. The speaker's own research, including studies on sensorimotor function in the lab and parabolic flight, will be emphasized. In addition, commercial suborbital space flights will be taking place in a few years, and the potential research that can be performed on these flights will also be discussed.
November 01, 2013 12:00p - 2:30p
In the cold and dense stages of star and planet formation, volatile molecules condense out on interstellar grains forming icy mantles. This condensation process results in a series of snowlines, or condensation fronts, whose exact locations are set by a combination of thermal and non-thermal adsorption and desorption processes. The icy grain mantles are also active chemical sites, resulting in a changing ice composition with time, typically to include an increasing fraction of complex organic molecules. The nature of these snowlines in protoplanetary disks are predicted to have large impacts on planet formation efficiencies, on the bulk compositions of the forming planets, and on the amount of prebiotic material available on planet surfaces. We have used a combination of IR and millimeter observations, theory, and laboratory experiments to characterize interstellar ices, snow line locations (i.e. where these ices are located), and the chemical and planet formation consequences of the exact locations of different snow lines. I will discuss how the outcome of these studies have impacted our understanding of ice formation during star and planet formation, and also future prospects as complete ALMA and the next generation of laboratory experiments come online.
October 04, 2013 12:00p - 2:30p
Recent advances in exoplanet observations and theoretical methods are leading to unprecedented constraints on the physicochemical properties of exoplanetary atmospheres, interiors, and their formation conditions. In this talk, I will present some of the latest results in this emerging frontier. I will present constraints on the atmospheric chemical compositions and temperature profiles for a variety of exoplanets based on infrared observations from a wide range of facilities including HST, Spitzer, and ground-based telescopes. I will discuss how these constraints are being used to understand various equilibrium and non-equilibrium processes in exoplanetary atmospheres, to develop new classification schemes for exoplanets, and to understand the conditions of their formation and subsequent evolution.
I will also present the latest constraints emerging on the atmospheres, interior structures, and formation environments of super-Earths, whose interior compositions span a wide gamut - from water worlds with thick volatile envelopes to super-Mercuries, lava planets, and carbon planets - thereby testing the limits of our understanding of planetary mineralogies and their equations of state under exotic astrophysical conditions. The exciting future prospects of characterizing exoplanetary atmospheres, interiors, and formation conditions, using current, upcoming, and future observational facilities will be discussed, along with several open questions of fundamental nature in the field.
May 03, 2013 12:00p - 2:30p
Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing exoplanet surveys and proposed space-based flagship missions. In this talk, I will discuss about our recent results on new estimates of HZs around Main-sequence stars. According to our new model, the inner and outer HZ limits for our Solar System are at 0.99 AU and 1.67 AU, respectively, suggesting that the present Earth lies near the inner edge. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may be broader than our estimates. Applying the new HZ limits to cool, low mass stars (M-dwarfs) in NASA's "Kepler" data, we find that potentially habitable planets around M-dwarfs are more common than previously reported. The mean distance to the nearest habitable planet may be as close as 7 light years from us.
April 05, 2013 12:00p - 2:30p
On Earth, microorganisms appear to inhabit all physical space that provides the minimum requirements for life. These include the availability of water, carbon, nutrients, and light or chemical energy. While these are generally abundant in surface or near-surface environments, their mode and distribution in the subsurface are poorly constrained. Nevertheless, it has now been shown unequivocally that archaea and bacteria inhabit deeply buried rocks and sediments where they contribute to biogeochemical cycles. All evidence suggests that these subsurface ecosystems are spatially enormous and diverse. On other planets, at least in our solar system, putative extant or extinct life would most likely reside underground or in massive ice shells. With a focus on near-by planets where landed missions are more than just a possibility, access to the subsurface will be highly desirable. Robust strategies for subsurface life detection on Mars, Europa, or other potential targets are poorly developed. The search for extant life or its biosignatures is scientifically and technologically extremely difficult; on Earth, it is a formidable but tractable challenge. Our cross-disciplinary team from the University of Southern California, the California Institute of Technology, the Jet Propulsion Laboratory, the Rensselaer Polytechnic Institute, and the Desert Research Institute (DRI) will develop field, laboratory, and modeling approaches aimed at detecting and characterizing microbial life in the subsurface—the intraterrestrials.
March 01, 2013 12:00p - 2:30p
In this talk, Glavin will describe the concept of a “habitable environment” and the requirements for life as we know it. Understanding the basic requirements for life and the prebiotic chemistry that led to the emergence of life on Earth will help guide our search for life on Mars. Glavin will also give an overview of NASA's Mars Science Laboratory mission with an update on the progress of the Curiosity rover and a summary of the analytical capabilities and measurement objectives of the SAM experiment. Curiosity is currently getting ready for the first SAM analysis of a drilled rock on Mars and will take a step closer to answering the question of whether Mars could have ever supported life.
February 01, 2013 12:00p - 2:30p
The final stages of the growth of a planet consist of violently energetic impacts, but new observations of the Moon and Mercury indicate that the energy of accretion does not remove all the water and carbon from the growing planet. Models demonstrate that rocky planets that accrete with as little as 0.01 wt% water produce a massive steam atmosphere that collapses into a water ocean upon cooling. The low water contents required indicate that rocky planets may be generally expected to produce water oceans through this process, and that an Earth-sized planet would cool to clement conditions in just a few to tens of millions of years. These results indicate that most rocky planets in our solar system and rocky exoplanets are likely to have been habitable early in their evolution, increasing the likelihood of life on the estimated 17 billion Earth-sized planets in the Milky Way.
November 02, 2012 12:00p - 2:30p
A promising path to the discovery and study of individual rocky planets in the Habitable Zone around a star is to search for planets around nearby M dwarfs, as their mass and smaller HZ planet orbits leads to a significantly larger Doppler radial velocity signal than that of the Earth on our Sun. Since the flux distribution mid-late M dwarfs peaks sharply in the NIR a stable high-resolution NIR spectrograph capable of delivering high RV precision in the bands is a promising route to detecting rocky planets. I will discuss significant advances in precision NIR spectroscopy that may help achieve this goal, on-sky tests with laser frequency combs, and the ongoing design and build of the fiber-fed Habitable Zone Planet Finder (HPF) high resolution spectrograph.
October 05, 2012 12:00p - 2:30p
Proteins play the primary functional role in nearly all of life's physiological processes. They are, themselves, the final products of the translation system, life's oldest and most highly conserved of these processes. The early expansion of protein functions and complex functional networks created the foundation from which cellular life emerged. Here, I describe ancient transitions in protein evolution that ultimately led to the sophisticated protein repertoire of the universal ancestor at the root of the tree of life.
May 04, 2012 12:00p - 2:30p
The first two billion years of life on Earth left scant, inconclusive material evidence of its existence, despite its undoubtedly complex and profound impact on our planetary system. As a consequence, many hypotheses about the origin of life and its early evolution are currently untestable. New lines of evidence are therefore necessary to construct a more precise, explanatory narrative relating these planetary events, and place them within an astrobiological context. The genomes of extant organisms can provide such a record, as they are descended from lineages that endured across nearly all geological time, and preserve within their sequences an accumulated signal of ancient evolutionary processes and events.
Using comparative phylogenomic analyses, ancient horizontal gene transfers between the ancestors of extant groups can be inferred, demonstrating the chimeric, coalescent nature of early evolution, with recombinations within transferred genes revealing the selective pressures that shaped these lineages. Such transfers also act as an internal calibration for the relative timing of evolutionary events early in the microbial history of life, analogous to the fossil stratigraphy that orders the history of complex life in later geological eras. The phylogenomic record even extends to the very ancient time before the Last Universal Common Ancestor (LUCA), as ancestral sequence reconstruction of protein families diverging before this time gives clues to the function of the most ancient proteins, and the evolution of the earliest biological processes.
April 06, 2012 12:00p - 2:30p
Over the past two decades, there has been an increasing awareness within the geological, microbiological, and oceanographic communities of the potentially vast microbial biosphere that is harbored beneath the surface of the Earth. With this awareness has come a mounting effort to study this potential biome -- to better quantify biomass abundance, activity, and biogeochemical consequences of this activity. In the Earth system, the largest deep subsurface biome is also the least accessible -- the deep igneous ocean subsurface biosphere. This subcrustal biosphere also has greatest potential for influencing global scale biogeochemical processes –the carbon and energy cycles for example, and other elemental cycles.
This talk will focus on recent studies designed to elucidate this subcrustal biosphere, and illustrate techniques and novel technologies employed to address them. Integrative approaches using molecular biological, in-situ experimental, mineralogical, and geochemical techniques will be illustrated.
March 02, 2012 12:00p - 2:30p
If planets could re-form or migrate inwards to just outside the Roche limit of white dwarfs stars, they would be warmed to Earth-like temperature for billions of years. These planets would be easy to detect in edge-on orbit via a large depth transit lasting a couple of minutes and repeating every 12 hours; thus, a ground-based transit survey of cool white dwarfs would be sensitive to Earth-sized planets in their habitable zones, should they exist in sufficient abundance. I will discuss the prospects for detection and characterization of Earth-like planets in the habitable zones of white dwarfs, as well as scenarios for planet formation and potential constraints on habitability.
February 03, 2012 12:00p - 2:30p
Several young gas giants in wide orbits (> 10 AU) have now been directly imaged. These exciting discoveries provide new insights into the formation and early atmospheric properties of giant planets. This talk will focus on recent attempts to measure the near-infrared spectra of two planets orbiting the star HR8799. These data have aided in the characterization of the planets’ cloud and chemical properties, but also highlight the many difficulties we face when modeling planet atmospheres.
The few planets imaged so far are just the beginning. New instruments, tailor made for high-contrast imaging, are coming online this year and will reveal dozens of young planets. These instruments will also obtain low resolution near-IR spectra of each new planet, providing a wealth of information across a wide range of planet masses and ages. Given the lessons we are learning from systems like HR8799, interpreting these data will be not be easy and significant observational and planet modeling obstacles must be overcome.
December 04, 2011 12:00p - 2:30p
Water is abundant on Earth, covering 75% of Earth's surface, and accounting for up to 0.1% of Earth's mass, yet Earth may in fact be a very dry world. Liquid water is not only key for life, but understanding the origin of Earth's water has important implications for habitability in both our solar system and in the numerous extrasolar planetary systems that have been discovered with planets within their star's habitable zones. This research question requires an interdisciplinary approach and is one of the themes for the UH NASA Astrobiology Institute (NAI). In the 1980's observations and models first suggested that comets might play a role in delivering water to Earth, and that the chemical fingerprint of this process was the D/H of ocean water. A more modern look at the problem now seeks to uncover all the issues related to the origin of Earth's water to identify the key unanswered questions and assess where these questions can best be answered by interdisciplinary approaches.
The UH NAI team is investigating the chemical composition of primitive bodies and evidence of aqueous processes in the early solar system, dynamical delivery of bodies to earth and the chemical signature of this delivery to earth. I will discuss the interdisciplinary perspective of the origin of Earth's water, in part as a consensus view from a recent workshop held in Iceland during Sep. 2011 to highlight where we are in our current understanding.
November 04, 2011 12:00p - 2:30p
Astronomy is entering an exciting new era where ground- and space-based observatories open windows on planetary systems increasingly similar to our own. In this talk I will give a brief overview of the search for exoplanets and discuss techniques that allow us to characterize the atmospheres of extrasolar planets. I will illustrate these from our work on detecting and characterizing exoplanets. I will also introduce a new observing technique that provides an exciting look into the atmospheres, clouds, and surface features of exoplanets. We are now applying this technique, rotational phase mapping, to ultracool brown dwarfs using both the Hubble and the Spitzer Space Telescopes. I will discuss the exciting first results from these studies and the future applications of the technique to super-earths and earth-like planets, as a step toward understanding planets in or near to habitable zones.
October 07, 2011 12:00p - 2:30p
In the next decade Mars will be visited by the most capable Rovers and instruments built to date. How will these missions find evidence of life on Mars and what does mean for us if there is no life detected. The robotic exploration of Mars and subsequent return of samples to earth will reveal a lot of information about our own origins whether or not life is discovered.
May 06, 2011 12:00p - 2:30p
Comets and carbonaceous chondrites are the remnants of molecular cloud material from which our Solar System formed. These bodies are considered to be primitive in the sense that they have been subjected to the least modification following accretion. Both comets and carbonaceous chondrites contain relatively large quantities of refractory organic macromolecular material. For many decades, a lack of consensus has existed as to the ultimate origin of these extraterrestrial organic solids, where confusion largely stems from the fact that throughout the Galaxy there exist many regions were extensive organo-synthesis occurs. Origins theories for primitive Solar System organic solids span from the lowest temperatures in the Interstellar Medium up to 1000 K in the inner Solar System. The best constraint on the origin of refractory organic solids is obtained by detailed studies of the organic solids directly. Using advanced spectroscopic techniques we have identified a plausible source for these organic solids and show that the organic solids in both comets and carbonaceous chondrites share a common origin. The broader implications of these results, both in terms of our understanding of the early history of the inner Solar System objects and the origin of life on Earth, lie in linking the unique properties of these organic solids to events that shaped the origin and evolution of Earth.
April 08, 2011 12:00p - 2:30p
As told by Maynard Smith and Szathmáry (The Major Transitions in Evolution, 1998) life's major transitions involve information and individuality. With equal justification, however, we can mark evolutionary milestones in terms of physiological innovation. A physiological complement to Maynard Smith and Szathmáry's list might include three major innovations associated with primary production (photosynthesis, oxygenic photosynthesis, and nitrogen fixation) and five that changed the face of heterotrophy (respiration, aerobic respiration, phagocytosis, bulk oxygen transport, and technology). Such a physiological perspective highlights interrelationships between evolving life and a physically dynamic planet. Geochemical data suggest that for much of the Proterozoic Eon, oxygen minimum zones of Earth's oceans tended toward euxinia. Under these conditions, nitrogen limitation would have favored primary producers capable of nitrogen fixation, as the geobiological record suggests. Despite the presence of oxygenic photoautotrophs, continuing anoxygenic photosynthesis likely played an important role in sustaining the redox structure of Proterozoic oceans. Late in the Neoproterozoic Eon, however, tectonic events appear to have nudged the biosphere toward a new state. Widespread rifting correlates with a switch from predominantly sulfidic to ferruginous waters in the OMZ; broadly coeval expansion of eukaryotes is consistent with the low sulfide tolerance exhibited by most eukaryotic clades. Four independent geochemical proxies suggest further redox transition 580-550 Ma, a time when rates of sediment accumulation increased markedly. Higher oxygen tensions and a receding challenge of anoxia likely facilitated animal diversification, but it was the evolution of anatomical mechanisms for bulk transfer that freed animals from the constraints of diffusion -- ushering in the age of bilaterians.
March 18, 2011 12:00p - 2:30p
The origin of life occurred in a complex geochemical environment, characterized by significant chemical and thermal gradients, fluid fluxes, cycles, and interfaces. These aspects of the prebiotic world are critical to understanding life's origins. Crystalline surfaces of common rock-forming minerals are likely to have played several important roles, including catalysis of key biomolecules; as interfaces for the selection, concentration and protection of those molecules; and as templates for the assembly of molecular structures. Thus mineral surfaces may have contributed centrally to the linked prebiotic problems of containment and organization by promoting the transition from a dilute "primordial soup" to highly order domains of molecules.
Robert M. Hazen, Senior Staff Scientist at the Carnegie Institution's Geophysical Laboratory and Clarence Robinson Professor of Earth Sciences at George Mason University, received the B.S. and S.M. in geology at MIT and the Ph.D. at Harvard University in earth science. He is author of 350 scientific articles and 20 books, including Genesis: The Scientific Quest for Life's Origin. A former President of the Mineralogical Society of America, Hazen's recent research focuses on the role of minerals in the origin of life, the co-evolution of the geo- and biospheres, and the development of complex systems. He is also Principal Investigator of the Deep Carbon Observatory, a 10-year project to study the chemical and biological roles of carbon in Earth's interior (http://dco.ciw.edu).
February 04, 2011 12:00p - 2:30p
In the coming decades, the search for life outside our Solar System will be undertaken using astronomical observations of extrasolar terrestrial planets. To better inform our search, the NASA Astrobiology Institute\'s Virtual Planetary Laboratory team uses a suite of computer models to explore the interaction between a terrestrial planet and its parent star. The resulting models allow us to simulate extrasolar terrestrial planetary environments and spectra, and to define and quantify likely signs of planetary habitability and life. This talk will discuss the VPL models and results to date, including the detectability of planetary habitability and potential signs of life from alternative biospheres.
December 10, 2010 12:00p - 2:30p
Over 400 planets have been found around nearby stars, but none of them is thought to be at all like Earth. The goal now is to identify rocky planets within the habitable zones of their stars and to search their atmospheres spectroscopically for signs of life. To do this, we need new space-based telescopes such as NASA's proposed Terrestrial Planet Finders or ESA's Darwin mission (all of which are indefinitely postponed at the moment). If spectra of extrasolar planet atmospheres can be obtained, the presence of O2, which is produced from photosynthesis, or O3, which is produced photochemically from O2, would under most circumstances provide strong evidence for life beyond Earth. But "false positives" for life may also exist, and these need to be clearly delineated in advance of such missions, if at all possible. I will also contrast my optimism about the search for complex life with the more pessimistic view expressed by Ward and Brownlee in their book, Rare Earth.
November 12, 2010 12:00p - 2:30p
A low-latitude distribution of continents may be a prerequisite for the global glaciations that appear to have affected Earth at least twice during the emergence of animals. However, a preponderance of low-latitude continents may also make Earth more susceptible to true polar wander, the process by which the mantle and crust spin relative to the fluid outer core to maintain rotational equilibrium. I will make a case for a pair of true polar wander events circa 800 million years ago that started a cascade of changes in the geochemical cycling between continents and oceans, and led to global glaciation. Did these changes in climate and ocean geochemistry finally allow the radiation of animals, or was it the first animals that modified geochemical cycling and climate?
October 08, 2010 12:00p - 2:30p
The oxygenation of the Earth's surface, which occurred ca. 2.3 billion years ago, is the earliest unambiguous imprint of biology on a planetary scale. Therefore, the search for molecular oxygen features prominently in the prospective search for life on extrasolar planets. However, the connections between the evolution of life and the evolution of the oxygen content of the Earth's atmosphere remain unclear. This talk will present emerging new perspectives on the Earth's transition from an anaerobic to an aerobic world.
September 03, 2010 12:00p - 2:30p
A fundamental challenge for astrobiology is to establish the relative contributions of chance versus predictability in the origin and evolution of life on our own planet. Thus, for example, all Earth-life creates metabolism from an interacting network of protein molecules that catalyze various biochemical reactions. Furthermore, early during evolution it had arrived at a standard set of 20 amino acid building-blocks with which to build each of these proteins. We now have good reason to think that many of these amino acids are formed in significant quantities throughout the galaxy - but so are many others - so would alien life be like us, and how could we possibly know?
June 18, 2010 12:00p - 2:30p
What is the best strategy for finding signs of life beyond the Solar System? Until recent years this was a purely philosophical question, but today we have the technical ability to search for signs of life on exoplanets around nearby stars, so the question is now a practical one. To start, we ask what kind of signs of life should we be looking for, and where should we be looking? Next we might ask about the methods we could use for such a search, and the kinds of evidence that we expect to obtain. Finally we can ask about the prospects for starting this search in the coming decade.
May 07, 2010 12:00p - 2:30p
The advent of cryogenic space-borne infrared observatories such as the Spitzer Space Telescope has lead to a revolution in the study of extrasolar planets and planetary systems. Already Spitzer has characterized the emergent infrared spectra of close-in giant exoplanets that orbit sun-like stars, using transit and eclipse techniques. Transits offer enormous advantages in characterizing the bulk properties (mass, radius) as well as the atmospheric composition of extrasolar planets. However, the nearest transiting and habitable extrasolar planet almost certainly does not orbit a Sun-like star. It orbits an M-dwarf star, and it could be a scant 10 parsecs distant from us, or even closer. After we find this unusual habitable world, we will characterize it using transit techniques. Already the ground-based MEarth survey has found a hot superEarth (T = 500 Kelvins) orbiting the M-dwarf star Gliese 1214, 10 parsecs from our own Sun. A space-based all-sky survey could extend the MEarth results to habitable-zone planets. When we have found such a world, the James Webb Space Telescope will be able to measure its atmospheric composition, and possibly even search for biosignatures.
April 09, 2010 12:00p - 2:30p
For the past decade missions to Mars have "followed the water". In this talk I will argue that future missions should begin directly searching for signs of life. The most important result from the recent Mars missions in this regard was the discovery of perchlorate by the Phoenix lander. Perchlorate could form the basis of a biological redox system on Mars. Furthermore, reanalysis of the Viking GCMS results suggests that perchlorate and organics may have been present at the Viking sites. Ice-cemented ground beneath dry permafrost in the high elevations of the Antarctic Dry Valleys provides a model for considering the search for signs of life at the Phoenix site.
March 05, 2010 12:00p - 2:30p
Formation scenarios of the solar nebula invoke two main reservoirs of water ice that may have taken part concurrently into the production of solids. In the first reservoir, which is located within the heliocentric distance of 30 AU, water ice infalling from the Interstellar Medium (ISM) initially vaporized into the hot inner part of the disk and condensed in its crystalline form during the cooling of the solar nebula (Kouchi et al. 1994; Chick & Cassen 1997). The second reservoir, located at larger heliocentric distances, is composed of water ice originating from ISM that did not suffer from vaporization when entering into the disk. In this reservoir, water ice remained mainly in its amorphous form. From these considerations, we discuss here the trapping conditions of volatiles in planetesimals produced within the outer solar nebula and their implications for the origin and composition of gas giant planets, their surrounding satellite systems and comets. In particular, we show that the formation of icy planetesimals agglomerated from clathrate hydrates in the solar nebula can explain in a consistent manner the volatiles enrichments measured at Jupiter and Saturn, as well as the composition of Titan's atmosphere.
February 05, 2010 12:00p - 2:30p
Iron and sulfur redox chemistry support chemoautotrophic subsurface microbial communities on Earth, and could potentially sustain a biosphere on Mars. In this talk, I will describe a highly productive ecosystem in an extreme natural environment that is supported by air, water, and iron sulfide minerals. Through integrating cultivation-independent molecular ('omic', imaging, and other) methods with geochemical approaches, it has been possible to begin to determine how these communities are structured and to unravel complex interdependencies, spatial organization, and evolutionary pathways.
January 08, 2010 12:00p - 2:30p
The terrestrial geologic record from actual rocks extends back to about 4.02 billion years ago (4.02 Ga). Before that time, what we know of the environment of the earliest Earth's surface from the time of formation to the start of the continuous rock record is constrained by inferences derived from chemical and isotopic studies of the oldest zircon grains (Zr-orthosilicate minerals) as old as 4.38 Ga found in younger rocks, physics of stars and how planets form, and molecular phylogeny. Silicate planets form hot, but cool on timescales shorter than the tectonic cycle. Bolide impacts subsequently become important modifiers of surface environments, but after the planetary "re-set button" was hit by the Moon-forming event, were more beneficial than deleterious to early forms of life. Surface temperatures were likely warm enough to stabilize liquid water even with a fainter young Sun since ca. 4.4 Ga. The oldest meta-igneous rocks are interesting in that aside from their antiquity, they are rather mundane mid-crustal lithotypes. Evidence from the Hadean zircons points to extensive recycling of crust at underthrust zones (plate tectonics?), generation of granitoid melts and of (widespread?) continental crust and liquid water. The oldest know meta-sediments (ca. 3.81-3.83 Ga) preserve chemical and isotopic signatures consistent with (but not proof of) elemental Sulfur metabolism, N-fixation, CO2-fixation, and photoferrotrophy. In sum, by the time the continuous rock record starts at ~3.7 Ga, all of the key features of the habitable Earth were already in place. To place firmer constraints on the establishment of the habitable Hadean, we need to find yet older rocks. I will provide an update on this quest.
December 04, 2009 12:00p - 2:30p
NASA's Stardust spacecraft returned samples from comet 81P/Wild 2 to Earth in January 2006. Examinations of the organic compounds in cometary samples can reveal information about the prebiotic organic inventory present on the early Earth and within the early Solar System, which may have contributed to the origin of life. Preliminary studies of Stardust material revealed the presence of a suite of organic compounds including several amines and amino acids, but the origin of these compounds (cometary vs. terrestrial contamination) could not be identified. We have recently measured the carbon isotopic ratios of these amino acids to determine their origin, leading to the first detection of a cometary amino acid.
November 06, 2009 12:00p - 2:30p
Phosphorus is a key element in biological systems, acting in cell replication as RNA and DNA, in cell structure as phospholipids, and in metabolism as ATP. Given its ubiquity in biochemistry, phosphorus was likely present in the origin or early evolution of life. I will discuss sources of phosphorus on the early earth, concentrating primarily on extraterrestrial sources of reduced oxidation state phosphorus compounds, and evidence that these sources were used by early biochemical systems. Additionally, I will show how these reduced oxidation state phosphorus compounds could act in prebiotic or early biochemical systems to generate both key biologic compounds and metabolic energy.