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2001 Annual Science Report

Carnegie Institution of Washington Reporting  |  JUL 2000 – JUN 2001

Executive Summary

Executive Summary — CIW (dm)

The astrobiology team led by the Carnegie Institution of Washington is studying the physical, chemical, and biological evolution of hydrothermal systems, including vent complexes associated with ocean ridges, deep aquifers, and other subsurface aqueous environments, both on Earth and on other Solar System and extrasolar bodies. Such diverse systems are important environments for life on Earth and possibly elsewhere in the cosmos. We also contiunue a strong observational and theoretical program related to understanding the formation and early evolutin of both our Solar System and extraterrestrial solar systems.

The traditional view of life’s origin on Earth has focused on processes near the photic zone at the ocean-atmosphere interface, where ionizing radiation provides energy for prebiotic organic synthesis. In the context of astrobiology, this origin paradigm restricts the initial “habitable zone” around stars to planets and moons with surface water. According to this view, subsequent adaptations on Earth, and possibly elsewhere, led to expansion of the biosphere into subsurface habitats.

An alternative hypothesis is that life-forming processes may also occur in subsurface hydrothermal environments at the water-mineral interface. This hypothesis, that life on Earth originated from oxidation-reduction reactions in deep hydrothermal zones, perhaps at or near ocean ridge systems, opens exciting possibilities for astrobiological research. If a subsurface, high-pressure origin of life is possible, then the initial habitable zone around stars is greatly expanded to aqueous environments where redox reactions can be driven along thermal and chemical gradients.

Several lines of evidence lend credibility to the hydrothermal origins hypothesis. Numerous recent discoveries of high-pressure life, especially lithotrophic prokaryotes, suggest that hydrothermal environments support abundant life. Models of the Earth’s formation postulate large, surface-sterilizing impacts as recently as 3.8 billion years ago, but deep hydrothermal zones may have insulated life from these traumas. Studies of molecular phylogeny reveal that thermophilic microbes are perhaps the closest living relatives of the last universal common ancestor. Finally, hydrothermal organic synthesis experiments reveal unexpectedly facile synthetic pathways. Whether or not life originated in a subsurface hydrothermal zone, these lines of evidence, coupled with the assumed widespread distribution of such environments in our Solar System and elsewhere, point to the need and opportunity for an intense study of the characteristics of hydrothermal systems.

Our consortium’s research activities explore the physical, chemical, and biological evolution of hydrothermal systems from these complementary fronts:

â?¢ We model planetary formation, and we detect and characterize extrasolar planets, in an effort to understand the range of objects that develop hydrothermal systems as well as the distribution of volatiles, especially water, within those objects.

â?¢ We investigate the circumstances under which hydrothermal systems form on planets and other bodies and the expected physical and chemical characteristics of those systems as they evolve.

â?¢ We study geochemical processes in hydrothermal systems, especially those that lead to abiotic organic synthesis. A particular focus is the role of mineral catalysis in these systems.

â?¢ We consider the origin and evolution of biological entities in hydrothermal systems through studies of the biochemistry of contemporary hydrothermal organisms.

A complete understanding of hydrothermal systems and their role in life’s origins requires dramatic advances on all of these fronts, as well as an extensive and challenging integration of these topics. During the past year we achieved significant progress in each of these research areas, as well as increased attention to the interfaces among these theoretical, experimental, and field approaches.

Among the highlights from the past year’s research in the area of planetary formation and evolution, members of our consortium

â?¢ Discovered 12 new extrasolar planets, including the second and third known examples of multiple-planet systems.

â?¢ Demonstrated that Jupiter-mass protoplanets can form from instabilities in a protoplanetary disk of a mass similar to the solar nebula.

â?¢ Demonstrated that Mars-size planetary embryos can form in the inner Solar System even in the presence of rapidly formed outer planets.

â?¢ Showed that the Tharsis rise on Mars was largely emplaced prior to the formation of late Noachian valley networks, and that the volcanic construction of Tharsis may have contributed significantly to the atmospheric inventory of water and other volatiles.

In the area of the evolution of organic matter and water in meteorites, we

â?¢ Demonstrated that shock waves in the solar nebula may have led to melting and chondrule formation as well as the breaking of N2 bonds to form nitriles, which can then polymerize or contribute to amino acid synthesis.

â?¢ Developed stringent new constraints on the characteristics of the Murchison organic macromolecule from Nuclear Magnetic Resonance experiments.

â?¢ Documented petrological evidence for pervasive premetamorphic aqueous alteration of ordinary chondrite meteorites, which implies a more sunward position of the water-ice condensation line than has been heretofore assumed.

â?¢ Discovered D-rich structural water in a post-stishovite silica phase in martian meteorites, providing additional evidence linking D-rich water and shock processes accompanying impact cratering on Mars.

â?¢ Developed improved inductively coupled plasma mass spectrometer techniques for precise measurements of Fe isotopes as a tool for identifying possible isotopic biomarkers.
group has

â?¢ Abiotically synthesized pyruvic acid â?? a key molecule for the emergence of biochemistry â?? under hydrothermal conditions.

â?¢ Identified a viable and robust “geochemical” ignition point for the prebiotic fixation of carbon under hydrothermal conditions.

â?¢ Synthesized vesicle-forming amphiphilic molecules from pyruvic acid under hydrothermal conditions â?? compounds strikingly similar to those extracted from the Murchison meteorite.

â?¢ Challenged the notion that formaldehyde/HCN chemistry led to amino acid formation on the primitive Earth by demonstrating that an early CO2/N2 atmosphere could not provide sufficient quantities of these precursors.

â?¢ Demonstrated that ammonia is readily synthesized from nitrate under hydrothermal conditions in the presence of a wide variety of transition-metal oxide and sulfide minerals.

â?¢ Developed experimental techniques for observations of fluid-phase behavior and “in situ” determination of organic reaction kinetics at hydrothermal conditions.

In the area of experimental tests of proposed hydrothermal organic synthesis reactions, our group has

â?¢ Abiotically synthesized pyruvic acid â?? a key molecule for the emergence of biochemistry â?? under hydrothermal conditions.

â?¢ Identified a viable and robust “geochemical” ignition point for the prebiotic fixation of carbon under hydrothermal conditions.

â?¢ Synthesized vesicle-forming amphiphilic molecules from pyruvic acid under hydrothermal conditions â?? compounds strikingly similar to those extracted from the Murchison meteorite.

â?¢ Challenged the notion that formaldehyde/HCN chemistry led to amino acid formation on the primitive Earth by demonstrating that an early CO2/N2 atmosphere could not provide sufficient quantities of these precursors.

â?¢ Demonstrated that ammonia is readily synthesized from nitrate under hydrothermal conditions in the presence of a wide variety of transition-metal oxide and sulfide minerals.

â?¢ Developed experimental techniques for observations of fluid-phase behavior and “in situ” determination of organic reaction kinetics at hydrothermal conditions.

In the area of supporting theoretical studies of hydrothermal synthesis reactions, we

â?? Established a global thermodynamic framework for metabolism in thermophilic and hyperthermophilic prokaryotes.

â?? Demonstrated that the hydrocarbons detected in ALH84001 likely were formed abiotically through reactions of CO and H2 in the presence of magnetite.

â?? Showed that the citric acid cycle may be derived from physical and chemical selection rules suggesting an emergent quality of the chemistry distinct to its environment.

In the area of biological studies of hydrothermal systems, members of our consortium

â?¢ Showed that hyperthermophilic archaea isolated from the subseafloor near deep-sea vents are phylogenetically and physiologically different from similar organisms isolated from vent sulfide structures.

â?¢ Described a novel and deeply rooted hyperthermophilic archaea which can grow on organic acids such as acetate and citrate with Fe (III) as the electron acceptor.

â?¢ Characterized the subsurface bacterial and archaeal communities at Axial Volcano, Juan de Fuca Ridge.

â?¢ Designed a molecular probe to detect the nitrogen fixation gene in archaea and successfully detected the gene in subseafloor hyperthermophiles.

â?¢ Demonstrated that Fe-oxidizing bacteria are widespread and play a substantial role in the deposition of Fe oxyhydroxide deposits in Fe-rich oxic-anoxic boundary habitats on Earth.

â?¢ Demonstrated the viability of biochemical activity at pressures exceeding 10,000 atmospheres.

â?¢ Demonstrated that calcite crystals, when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of D- and L-enantiomers on pairs of mirror-related crystal growth surfaces, thereby providing a plausible geochemical mechanism for chiral selection and subsequent homochiral polymerization of amino acids on the prebiotic Earth.

Under a new project initiated this past year, members of our team are developing protein chip-based molecular recognition technology as a method for detecting life on Earth and other Solar System bodies. The Ciphergen Biosystems Protein Chip Read utilizes the surface chemistry of small chips to capture selectively femtomole amounts of complex mixtures of organic molecules for molecular weight determination by time-of-flight mass spectrometry. Together with collaborators from several other NAI teams, our group has begun to intercompare different types of organic molecules. An initial study demonstrated that microbial proteins, biologically produced but chemically modified microbial molecules, and abiotically synthesized organic matter can be distinguished on the basis of their respective mass spectrometric characteristics.

Finally, our team hosted the second General Meeting of the NASA Astrobiology Institute at the Carnegie Institution of Washington’s administrative headquarters, and one of our Co-Investigators chaired the program committee for the meeting.

In summary, our team’s recent research, including discoveries of new planetary systems, exploration of possible hydrothermal regimes on other worlds, elucidation of robust hydrothermal synthetic pathways, documentation of novel microbial metabolic strategies, and finding unexpected high-pressure environments for life, inform the central questions of astrobiology. Taken together, these discoveries are changing our views of life’s origin and its distribution.






Finally, our team hosted the second General Meeting of the NASA Astrobiology Institute at the Carnegie Institution of Washington’s administrative headquarters, and one of our Co-Investigators chaired the program committee for the meeting.
In summary, our team’s recent research, including discoveries of new planetary systems, exploration of possible hydrothermal regimes on other worlds, elucidation of robust hydrothermal synthetic pathways, documentation of novel microbial metabolic strategies, and finding unexpected high-pressure environments for life, inform the central questions of astrobiology. Taken together, these discoveries are changing our views of life’s origin and its distribution.