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Executive Summary

The Evolution of a Habitable Planet

The Penn State Astrobiology Research Center (PSARC) was created in 1998 as part of the NASA Astrobiology Institute. PSARC currently comprises 19 (Co)-PIs and their research teams from The Pennsylvania State University (Mike Arthur, Sue Brantley, Lisa Brown, Jean Brenchley, Will Castleman, Greg Ferry, Kate Freeman, Blair Hedges, Chris House, Jim Kasting, Lee Kump, Jenn Macalady, Hiroshi Ohmoto, Mark Patzkowsky, Steinn Sigurdsson, and Alex Wolszczan), The University of Pittsburgh (Rosemary Capo and Brian Stewart), and SUNY Stony Brook, Martin Schoonen). During the period of July 1, 2006 — June 30, 2007, PSARC has supported all or part of the research/education/PO activities carried out by 96 persons (19 (Co)PIs, 6 research associates, 9 postdoctoral fellows, 43 graduate students, 14 undergraduate students, 1 technician, and 4 staff in administration/IT/EPO). The total number of PSARC personnel, especially the graduate students, increased by about 10 percent. In addition, 36 Associate Members for Research (who are mostly professors at other institutions) closely collaborate with the 19 (Co)-PIs. Three other Associate Members work closely with the EPO team. About 70 peer-reviewed papers were published by PSARC members during the period 7/1/06 — 6/30/07.

Research

PSARC’s research has focused on critical issues concerning planetary habitability : (1) the evolutionary history of the biosphere, hydrosphere, and atmosphere on Earth and other planets, specifically the times, causes, and consequences of the emergences of major organisms (e.g., cyanobacteria, methanogens, sulfate reducers, fermenters, sulfide oxidizers, and eukaryotes); (2) the effects of photochemical reactions on the early biosphere; and (3) detection of biosignatures on other planets. Our approaches to these critical issues, and some important achievements during the last year, are briefly summarized below:

I. Investigations of the Geochemical Record of the Earth’s Early Biosphere. Ohmoto’s group continued mineralogical and (bio)geochemical investigations of seven cores from the 2003-2004 ABDP (Archean Biosphere Drilling Project) drilling. They also conducted a 3-week field investigation of the “probable lateritic paleosols” that developed on the oldest land surface ~3.4 Ga ago in the Pilbara Craton , Western Australia , and laboratory investigations of these samples. These investigations yielded a variety of data suggesting that by ~3.4 Ga: (1) an extensive biosphere developed on land, as well in the oceans; and (2) the atmosphere-ocean system became O₂ -and CO₂ -rich, and CH₄ -poor.

Arthur and Kump groups published three papers on the Permian mass extinction, exploring disturbances to the C and S cycle through the event and into the Triassic. Suggestive links to Siberian Trap volcanism and subsequent development of highly sulfidic oceans have been found in the analysis of the C and S isotopic composition of Late Permian carbonates. They also began geochemical studies of paleosols in South Dakota and Iowa to investigate changes in the biosphere during the latest Precambrian — Cambrian period.

PSARC obtained a NAI Director’s Fund to organize Field Workshop “Biosignatures in Ancient Rocks”, during September 17 — 27, 2007 in Sudbury and other areas in Ontario , Canada .

II. Investigations of Photochemical Reactions of Sulfur and Iron in the Early Earth. The mass-independently fractionated sulfur isotopes (MIF-S), primarily found in pre-2.4 Ga sedimentary rocks, has been interpreted by many geoscientists as the products of UV photolysis of volcanic SO₂ in an O₂ -poor atmosphere. Castleman’s group has been conducting laboratory experiments on photochemical reactions of SO 2 by utilizing a reflectron time-of-flight mass spectrometer (RETOF-MS) and a femtosecond laser system coupled with the pump-robe technique. They found that the photolysis of 32 SO₂ and 34 SO₂ were strongly affected by pump wavelength (~200 to 197 nm) and power.

From entirely different types of laboratory experiments, Watanabe and Ohmoto have succeeded in creating MIF-S signatures in the H₂S that was generated from thermochemical reduction of sulfate; this may suggest that the MIF-S signatures in some Archean sediments may have been caused by diagenetic reactions between sulfate and organic matter. Ohmoto’s group also discovered in ABDP core samples that MIF-S signatures are absent in some major Archean sedimentary formations. This discovery suggests the following three possibilities for interpreting the MIF-S record: (i) the atmospheric O₂ level fluctuated from anoxic to oxic during the Archean; (ii) the MIF-S signatures were created during intensive volcanism; and (iii) the MIF-S signatures were not related to atmospheric reactions. Kasting’s group proposes that the absence of MIF-S in some Archean sedimentary rocks may represent the period(s) of development of a thick organic haze in the atmosphere. They have also developed a model linking the oxygen isotope record of cherts through geologic time to the tectonic history.

III. Investigations of Genomic Record of the Earth’s Early Biosphere. Hedge’s group released database ( TimeTree and TimeTree2, http://www.timetree.org ) of 2923 published divergence times among organisms. They have also completed a study on prokaryote evolutionary history using all available genome sequences. Ferry’ group has identified that one of the genes in Methanosarcina acetivoran, MA3736, which had been linked by previous researchers to an enzyme required for aerobic growth with aromatic compounds by species in the Bacteria domain ,  is the prototype of a previously unrecognized protein disulfide reductase family which contains an intermolecular Fe-S cluster that controls oligomerization as a mechanism to regulate protein disulfide reductase activity.

IV. Laboratory Microbial Simulations: Astrobiological Signatures. From a variety of laboratory experiments, House’s group has made significant progress in understanding the interplay between trace metals and nitrogen fixation in early ocean. Through a variety of microbes-mineral reaction experiments, Brantley’ group has continued to increase our understanding of: (1) the mechanisms that a variety of microbes obtain bioessential metals (e.g., Fe, Mn, Ni, Cu and Mo) from rocks ; (2) how these metals are utilized in microbes; and (3) how the kinetics of biochemical and isotopic reactions involving isotopes of Fe, Mo and Cu differ under different (bio)geochemical conditions. Brantley’s group has also compiled field terrestrial persistence ages for 8 common rock-forming phases (plagioclase, volcanic glass, quartz, feldspar, micas, pyroxene, amphibole, and olivine) collected from dated chronosequences representing a wide climatic spectrum ranging from -10°C to 30°C mean annual temperature and 400 mm to 4500 mm mean annual precipitation. The extent to which these minerals persist may help constrain the rates at which primary phases weather under field conditions on Earth, and likely represent minimum mineral persistence times on Mars if pH values were similar.

V. Investigations of Modern Analogues of Precambrian Microbial Ecosystems. From investigations of sulfur and nitrogen isotope systematics in modern anaerobic environments at oxic/anoxic interfaces in the Black Sea and Fayetteville-Green Lake , they recognized the importance of water-column processes in particulate N fluxes to sediments and their isotopic values. Brantley’s group has investigated basalt and olivine weathering in a Mars analog environment, the Sverrefjell volcano in Svalbard . They identified that: (a) the main source of biotic weathering in the arctic is probably lichens, which are known to release organic acids and "lichen acids”; (b) physical weathering plays a larger role than chemical weathering in this environment. 

Macalady’s group conducted fieldwork and sampling of snottites (pH 0-1 biofilms) for geochemistry and microbial genomics in four sulfidic cave systems hosting extreme acidophile communities, the Frasassi Caves and Grotta Nuova del Rio Garaffo in Italy, and Cueva de Villa Luz and Cueva Luna Azufre in Mexico. Among the sequences represented in the preliminary metagenome of a snottites are genes which code for functions relevant to metabolism and survival in the extremely acidic, sulfur-rich environment. Brenchley’s group continued investigations (phylogenetic and morphological analyses; growth and culturability) of psychorphillic (cold-loving) microorganisms and their cold-active enzymes to increase understanding their roles in the biosphere on Earth, the Moon, Mars, and Europa.

House’s group is investigating microbial communities in the Fayetteville-Green Lake and also those in starved marine sediments. House has obtained a NAI Director’s Fund to initiate an investigation of molecular biosignatures of life in the Dead Sea as a Mar’s analogue.

VI. Investigations on Planetary Habitability and Life Detection. Sigurdsson’s group has completed: (1) Theoretical model of post-migration planet formation; (2) analysis of Sptzer Space Telescope data; and (3) analysis of Hubble Space Telescope data to followup observation doing direct imaging search for giant planets around nearby white dwarfs obtained in current cycle. Wolszczan’s group has continued a search for planets around K-giants with the Hobby-Ebbery Telescope (HET). They have collected multiple epoch observations for ~400 stars out of the ~1000 targets in their observing list, and discovered that at least 30 of these 400 stars may have giant planets around them.

Fieldwork : Geologic field work was conducted in: (1) the Pilbara district, Western Australia by Ohmoto’s group to investigate the geology of the ABDP drilling sites and of 3.4 Ga paleosols (4 weeks, July, 2006); (2) the Sudbury — Temaagami — Cobalt — Timmins area, Ontario, Canada to scout possible sites for NAI Field Workshop by Ohmoto and Watanabe (2 days, June, 2007); (3) central Italy sulfide caves by Macalady group for geochemical measurements and sample collection of extremely acidic snottite biofilms for genomic analysis (3 weeks, May-June, 2007); (4) Tavasco sulfide caves, Mexico by Macalady group for geochemical measurements and sample collection of extremely acidic snottite biofilms for genomic analysis (3 weeks, February, 2007); and (5) Fayetteville Green Lake, New York by Kump, Arthur, Freeman, House and their students to investigate the microbial ecology and to collect water and microbial samples for laboratory simulators (July, 2006 — June, 2007).

Education and Public Outreach

Public Outreach: Three five-day astrobiology workshops for high school teachers were held during the summer of 2006: “Evolution” in July, “Planet, Star, or Neither?” in July, and “Origins of the Cosmos” in August, 2006. PSARC faculty and graduate students presented talks and exhibited posters describing their Astrobiology research and worked with the general public on hands-on experiments to increase the public’s awareness of Astrobiology on a number of opportunities. An Astrobiology Exhibit, with displays of illustrations, cores, and outcrop samples from the ABDP, created in a newly renovated Museum of the College of Earth and Mineral Sciences in 2005 continued to attract a large number of visitors.

Undergraduate Education: Astrobiology Minor Program, established in Fall 2000, as inter-college undergraduate program, had five students from the Departments of Geosciences, Astronomy, Microbiology, Biology, and Mathematics. It is administered by Jenn Macalady. A total of 17 undergraduate students were involved in a variety of research carried out by the 19 (Co)-PIs. Ovcr 1,500 students per year are enrolled in the 13 astrobiology-related undergraduate courses.

Graduate Education: A Dual-Title Ph.D. Degree Program in Astrobiology, inaugurated in August 2004, currently has 13 graduate students. The dual-title program is under the direction of Lee Kump.