Series Presentations

Andrew Knoll (Harvard University)

Abstract available soon.

Vikki Meadows (Caltech)

Abstract available soon.

James Kasting (Penn State University)

Abstract available soon.

Ariel Anbar (Arizona State University)

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.

Stephen Freeland (Institute for Astronomy, University of Hawaii)

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?

Wes Traub (Jet Propulsion Laboratory, Caltech)

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..

L. Drake Deming (NASA Goddard Center for Astrobiology)

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.

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Chris McKay (NASA Ames Research Center)

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.

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Olivier Mousis (Observatoire de Besançon, France)

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.

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Jill Banfield (University of California, Berkeley)

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.

Stephen Mojzsis (University of Colorado)

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.

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Jamie Elsila Cook(GSFC/Goddard Center for Astrobiology)

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.

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Matthew Pasek (University of South Florida)

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.

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