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Executive Summary

In this, our fourth year, many of our group have come into full productivity. Our NAI sponsored research at the University of Washington has concentrated on the following important astrobiological questions:

1. What are the characteristics of planets that can evolve complex organisms?
2. Where might such planets occur?
3. How does biological complexity evolve on a planet, and how might it end?
4. What are the limits and permissible chemistries of life and how might they arise?

During the 2004-2005 period significant progress into these problems was made. Below, our results and progress is summarized based on specific research problems defined in our original proposal.

How often, where, and under which conditions do habitable planets form and persist?
Even a decade ago we could not, with confidence, predict how many planets there might be beyond our own solar system. Now the rate of planet discovery is dizzying. But how many of these planets are habitable? While there was no indication that there was anything special about our own solar system and star that would make us unique in having planets, there was no real data to the contrary. Now there is definite evidence that planet formation is not only common, but might be ubiquitous to every region in our Milky Way Galaxy, and perhaps in most or all of the far flung galaxies making up the known Universe. We have gone from asking, “how many stars have planets”, to “how many planets have life?”

We define a habitable planet as a solid body capable of supporting life, as we know it. The study of extra-solar habitable planets involves a broad interdisciplinary approach that extends from understanding how planets are formed to understanding the conditions that allow such life to originate, survive, and evolve.

As one approach to understanding the evolution of habitability, Co-I Tom Quinn and his team have studied solar system formation with computer models. During the past year (2004-2005) Mejia and Quinn in collaboration with Mayer (Zurich) have continued performing simulations of giant planet formation by fragmentation of a gaseous disk. They are also investigating the dynamics of gas and dust interaction in protoplanetary disks. Dust may also move into the higher density regions of a fragmenting disk giving an alternative mechanism for forming giant planet cores.

Lufkin and Quinn performed simulations of giant planet migration and accretion in gaseous disks, while Barnes and Quinn in collaboration with Lissauer (Ames) continue their simulations of planetesimal accretion in the terrestrial region.

Barnes and Quinn continue to investigate the stability of extra-solar planetary systems as they are being discovered. They continue to find that most planetary systems, including our own, are on the edge of being unstable. This has implications for the efficiency of planet formation. Barnes and Raymond have also been investigating the formation of terrestrial planets within these known extra-solar systems.

Finally, Quinn and Kaib are starting to investigate the formation of cometary Clouds under various galactic contexts. They are also investigating the resulting impact history of comets on terrestrial planets. This latter area allows bridges to both the Impact group at the University of Washington, as well as the NAI Impact Focus Group.

What caused the delivery and retention of organics and volatiles through Earth History? What are the relative roles of large comet and asteroid fragments and interplanetary dust particles (IDPs) in bringing these materials to a planet? Co-I and project leader Don Brownlee and his post-Doc, G. Matrajt, have made a significant breakthrough: In collaboration with S. Taylor and S. Pizzarello, they discovered the first amino acids in extraterrestrial dust. The concentration of AIB in these 100µm samples is being used as a basis for estimating the total delivery rate of amino acids to the early Earth over the time period when dust accretion by Earth was greatly enhanced by the early evolution of the asteroid belt and the comet belts. These samples will soon be augmented by comet samples to be returned by the Stardust mission. All of these materials are believed to be identical to the particles that carried extraterrestrial organic materials to Earth during Earth’s prebiotic history.

Matrajt and Brownlee have also explored the survival of a variety of organics that are carried in small extraterrestrial particles. They built a special furnace that duplicates the ~5 second heat pulse and atmospheric environment that entering particles are exposed to. They have made10µm thin films of nano-porous alumina particles impregnated, in different runs, with lysine, coronene, and 2 pentadecanone (a ketone) and exposed them to the simulated atmospheric entry heating environment. By measuring pre and post-heating concentrations with GC/MS and electrospray/MS, they have been able to determine survival curves with temperature. Remarkably, all three of these relatively volatile compounds survive at the several percent level for the dynamic pulse heating to 600 C, a common maximum temperature during atmospheric entry. Lesser amounts survive even a >800C!

How do mass extinctions and impacts affect the evolution and survival of complex organisms, i.e., the long-term habitability of planets?
Large impacts are the norm for all bodies, habitable or not. Project leader Ward and his team consisting of Ken Farley, Roger Buick, Joe Kirschvink and David Kring have been concentrating on impacts.

Impacts can have major effects on the evolution of macroscopic life (e.g., ocean sterilizing events, dinosaur extinctions). However, we don’t understand the details of these effects and how they might affect in different ways various environments and types of organisms and survivability. If we are to seek existing or past life elsewhere, we should understand how those planets’ history of impacts might have affected the evolution of those organisms. We also want to know what predictions can be made about fossil and current life at different time periods, environments, and locations on other habitable bodies. These areas were examined in the 2004-2005-time interval.

Abundant new data indicate that we need both a concerted new examination into the effects of large body impacts on habitable planets and moons, and a critical re-examination of what has happened on and to Earth because of its own impact history. Mass Extinctions (MEs) during the Phanerozoic have been major factors in determining the make up of metazoan life on Earth, and have been intensely studied for decades, but there is still controversy as to cause(s). Until recently, we had an agreed-upon cause only for the “End Cretaceous” event (formerly the K/Tertiary, now officially renamed K/P, i.e., K/Paleogene, which is the term we will use here) among the “Big Five” MEs (K/P, Ordovician, Devonian, Permian/ Triassic [P/T], and Triassic/Jurassic [T/J]). That cause is large body impact — specifically, environmental effects following the Chicxulub impact of 65 My BP. But new results from drilling work in the crater itself has led one group to ask if this impact is the same age as the K/P mass extinction. Cause(s) of the other four remain controversial: most commonly invoked are impact, climate change, atmospheric gas compositional change, or some combination of these. Both the P/T and T/J MEs have been linked to (a) extrinsic causes (large body impacts), and (b) competing hypotheses of intrinsic causes. The association of flood basalt volcanism with the P/T, T/J, and K/P extinctions has caused the community to reconsider whether the Chicxulub impact was the sole or even major contributor to the K/P extinction, especially in deeper marine communities. This year our mass extinction group published two major papers on the Permian mass extinction in Science, as well as others on the Triassic/Jurassic mass extinction in refereed journals. As yet we cannot find evidence that either of these events was caused by impact.

Laboratory work continues on samples from the Permian-Triassic boundary in Africa and Canada, and the Triassic-Jurassic boundary in the Queen Charlotte Islands, Nevada, Italy, and the Newark Basin. We made new collecting trips to the Queen Charlottes, Nevada, and are finishing lab work on samples collected in early 2004 from New Zealand. During the year we continued to analyze samples from previous fieldwork for evidence of shocked quartz, Helium3, Iridium, and carbon isotopes.

What can we learn from the geological and fossil record about the evolution of eukaryotes and metazoans?
During the 2004-2005 interval co-I Buick concentrated on finishing the drilling of three deep diamond-drill cores in Australia for the NAI Astrobiology Drilling Program. This work took place during July-August 2004. These were completed through

1. the unconformity between the Coonterunah (3.52Ga) and Warrawoona (3.45Ga) Groups: 350 metres;
2. the lower Hamersley Group (2.65-2.47Ga): 1000 metres;
3. the Tumbiana Formation of the Fortescue Group (2.72Ga): 250 metres.

Notable intersections were: 1) a thickened basal sandstone unit to the Strelley Pool Chert in the Warrawoona Group; 2) two meteorite impact spherule horizons in the Wittenoom Formation; 3) ooid grainstones and evaporitic horizons in the Tumbiana Formation Uncontaminated samples for organic geochemical investigation were collected immediately upon surfacing, which yielded confirmation that indigenous biomarkers compatible with host-rock thermal maturity are indeed preserved.

Other fieldwork was conducted in the 3.52Ga Coonterunah Group, collecting samples for carbon isotope studies of metamorphosed early Archean sediments for comparison with older and more metamorphosed rocks from Greenland (Harnmeijer & Buick, 2005).

Ongoing Studies included organic geochemistry of Paleoproterozoic oil-bearing fluid inclusions, to confirm the syngenetic origin of biomarkers, and organic geochemistry of mid-Archean shales, to extend the temporal biomarker record.

What can the study of life in ice tell us about the potential for life beyond the Earth?
During 2004-2005 post Doc Joe Marx of the Deming group studied the role of exopolymers in facilitating bacterial activity, including specific enzyme activity, and survival under extreme conditions. During this year he showed that exopolymer production by a cold-adapted bacterium, Colwellia psychrerythraea strain 34H, goes up whenever the cells are stressed either by suboptimal growth temperatures, hydrostatic pressures, and available nutrient supply. These experiments will complement earlier work by Deming student Karen Junge, addressing what it takes for a bacterium to survive in deeply frozen ice formations rather than be active.

Another area of research this year was in looking at the role and biology of viruses in cold environments. Deming student Llyd Well has one paper in press (discovery of elevated concentrations of Archaea in cold Arctic waters), another submitted (viral lysis of bacteria and bacterial growth at -12°C in winter sea-ice brines — novel, with implications for lateral gene transfer in the cold), a third under review (lytic and lysogenic viruses in Arctic winter waters), and a fourth, the complete description of the novel virus he has obtained that lyses our model Colwellia bacterium in the cold, in preparation.

Finally, Deming worked with colleagues at The Institute for Genomic Research to complete the annotation and analysis of the cold-adapted Colwellia genome, which will soon appear in a paper in PNAS. Unusual findings include the presence of Archaeal genes (possible evidence for cross-Domain lateral gene transfer) and a record number of genes encoding for proteins and other compounds destined for export from the cytoplasm.

During this past year co-I Steve Warren began discussions with the Deming group about future collaboration. Warren has been studying models that pertain to the ancient “Snowball Earth” events of the PreCambrian. These intervals of time when the Earth may have gotten cold enough to freeze all, or some portion of the oceans remains controversial. The connection of the Warren research to the studies of cold life is a first step in understanding the effect that such events may have had on Earth’s biology during cold intervals.

Evolutionary pathways by which microbes and their communities evolve, and by which complex organisms originate.
Three separate groups carried out our team’s investigations into specific microbes and microbial communities that are not in ice: the Staley lab, the Leigh lab, and the Stahl lab.

During the past year co-I Staley and his group have shifted focus toward anaerobic communities in the Black Sea, as well as continuing work on tubulin and the origin of eukaryotes and the cytoskeleton.

With regard to the anaerobic microbes of the Black Sea, the Staley lab has begun investigations of a novel reaction, the anammox (anaerobic ammonia oxidation) reaction in which ammonia is oxidized anaerobically as an energy source and nitrite is the electron acceptor. Importantly, the anammox reaction is carried out by a group within the Planctomycetes phylum. They are also looking at denitrification (Oakley et al, in preparation), thiodenitrification and nitrogen fixation. These results also reveal novel clades within the Planctomycetes whose function is not yet understood. The goal is to determine what the activities are of each of the novel clades and also determine which organisms are responsible for denitrification, thiodenitrification and nitrogen fixation.

The Staley lab has also worked on cold life. This year the Staley lab discovered that Psychromonas ingrahami grows at —12°C, the lowest temperature reported for a bacterium with an authenticated growth curve. Staley is now comparing this organism with its south polar counterpart, which is a member of this same species.

The John Leigh lab is also looking at anaerobic microbes, in their case methanogens. This past year, Leigh and his colleagues studied the response of M. maripaludis to hydrogen limitation, as well as studying electron flow in the process of methanogenesis. To do this, Leigh made mutations in genes involved in the various steps in methanogenesis to determine the roles of these enzymes.

The third co-I in this project is Dave Stahl. The primary research objective of Stahl’s lab is to better understand the origins and adaptive radiation of an ancient and biogeochemically significant assemblage of microorganisms, the sulfate-reducing prokaryotes (SRP). Research activities addressing this objective included field studies of SRP in habitats possibly similar to those that existed on early Earth (microbial mats and hot springs) and comparative sequence analysis of genes encoding the pathway for sulfate respiration.

Perhaps the most important finding of the Stahl group during the 2004-2005 reporting period concerns the importance and mechanisms lateral gene transfer (LGT) in the evolution and adaptive radiation of sulfate-reducing prokaryotes. A more complete understanding of LGT was obtained by conducting a census of SRP in diverse environments using a combination of molecular and cultivation dependent methodologies. Molecular analyses focused on the direct inspection of the genes (dsrAB) encoding a key enzyme (dissimilatory sulfite reductase) in the pathway for sulfate respiration. This work was aided by collaboration with Dr. Michael Wagner’s laboratory (University of Vienna), utilizing complete analysis (examining 16 new reference cultures) of lateral gene transfer among cultured species of sulfate-reducing microorganisms. These studies have more clearly resolved the multiple lateral transfers of dissimilatory (bi)sulfite reductase genes (dsrAB) between major lineages. A major result of this more comprehensive analysis was the first discovery of a possible donor lineage among extant sulfate-reducing microorganisms.

Field work during the study period was undertaken at two hot springs in Yellowstone National Park, (Obsidian Pool and Black Sediment Pool), the Shoshone Geyser Basin, and at Guerro Negro in Baja California. Sediments collected from OP and BSP were used to inoculate enrichments in defined synthetic medium containing sulfate (~25 mM) and a variety of organic electron donors or hydrogen. Enrichment cultures were incubated at 60˚C or 80˚C. At 60˚C, sulfide production and growth were observed after 3-10 days with acetate, lactate, pyruvate, propionate, hydrogen, and a complex mixture of short chain fatty acids and yeast extract when inoculated with sediment from both OP and BSP. No sulfide was detected when ethanol, benzoate or a casamino acid mixture were added. Stahl found that there is greater metabolic diversity, defined by the pattern of electron donor usage in enrichment cultures, at 60˚C than at 80˚C. The preferred utilization of hydrogen as electron donor at 80˚C by SRP enrichments from both OP and BSP supports the proposed importance of H2-based lithotrophic metabolism at higher temperatures in Yellowstone hot springs.

Sediments and mats from seven springs in the Shoshone Geyser Basin were examined for endogenous sulfate reduction rates (SRR). It was found that this system appears to be related to sequences previously recovered from a geothermal feature near Bath Lake Vista in Mammoth Hot Springs.

At the Guerrero Negro Microbial Mat Community (Baja Sur, Mexico), it was observed that photosynthesis drives highly predictable diel fluctuations of chemical structure in microbial mat communities, most notably as manifested by periodic extremes of oxygen and sulfide at the near surface. A combined molecular and chemical fine-structure mapping of a hypersaline microbial mat in Guerrero Negro (Baja Sur, Mexico) related diel variation in depth and regional community structure to changing chemical structure.

Finally, progress was made in isolating and culturing the microbe Ammonifex degensii. These isolates comprise a closely related assemblage (~98% 16S rRNA sequence similarity) loosely affiliated with described Ammonifex (ca. ~90% 16S rRNA sequence similarity) and likely represent a new genus of sulfate-reducing bacteria.

The variety of life
The University of Washington team added Stephen Benner to its group in 2003-2004. Benner and his colleagues have been investigating alternatives to “life as we know it”, as well as studying chemical pathways to the formation of RNA and other biological molecules and materials. During 2004-2005, Benner and his team made progress in synthesizing DNA with 6 and 8 nucleotide “letters”. Benner has also collected with Chris McKay in an effort to identify various kinds of organics in the natural world.

The role of plate tectonics
Co-I Solomatov has been studying the role of plate tectonics in Astrobiology. Plate tectonics play an important role in the evolution of global planetary climate and life. Yet, there is very little consensus on when and how plate tectonics began on Earth. In 2004-2005 Solomatov made progress in modeling the initiation of plate tectonics be deriving a 3-D scaling relationship for spherical shells that stand in for a planet’s density layers. This is a conceptual improvement over previous models.