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Executive Summary

Introduction

The UCLA astrobiology research program comprises four broad themes. These are: 1) extrasolar planetary systems and the origins of organic molecules; 2) habitability of planets and their satellites; 3) Earth’s early environment and life; and 4) evolution of biological complexity. Milestones achieved this year include demonstration that water was extant on Earth within 200 million years of the formation of the solar system, detection of organic molecules in debris disk surrounding a nearby star, detection of an extrasolar analogue to our own Kuiper belt, direct imaging of extrasolar planets, establishment of a time scale for rock formation in our solar system, elucidation of the causes of transition metal isotope fractionation that might be used as a biomarker, and a significant revision to our view of Earth’s “tree of life.” The projects reported on in this annual report can be grouped according to the four themes described above. Some of the results of these studies are summarized below.

Extrasolar planetary systems

As part of a French/American team, UCLA astronomers reported discovery of two young planets. The targets of the study were among the list of stars identified previously by the UCLA lead team as most likely to harbor warm, young planets that could emit enough infrared light for detection from Earth-based telescopes. The two new planets were imaged in the infrared wavelengths using adaptive optics techniques at the “Very Large Telescope” in northern Chile . These objects are the first planets to be directly imaged outside of our solar system. Detection of planets by gathering their emitted light, rather than relying on their indirect gravitational influences on their star, represents a substantial step forward in the planet hunting field. One of the planets orbits a star, the other orbits a brown dwarf (a star-like object lacking sufficient mass to ignite as a true star). The planet that orbits the brown dwarf has a mass about 5 times that of Jupiter. This is the first time a planet has been detected in orbit around a brown dwarf by any observing technique, direct or indirect.

Several of the UCLA lead team astronomers are reporting this year discovery of a uniquely dusty sun-like star (BD+20 307). Previously, NASA’s IRAS satellite had been used to pinpoint hundreds of main sequence stars that are orbited by particulate matter located in regions analogous to the Kuiper-Belt of our solar system. The Kuiper belt , located out beyond the orbit of Neptune , is populated by Pluto-like, asteroidal-size objects composed of ices and rock. Collisions among the icy-rocky bodies there produce dust. IRAS found very few extrasolar analogs of the asteroid belt and zodiacal light regions that are vestiges of planet formation present in our solar system within a few Earth-Sun distances (astronomical units, AU) from the Sun. From mid-infrared measurements at the Keck and Gemini telescopes at Mauna Kea Observatory, the UCLA group found that BD+20 307 is orbited by dust somewhat analogous to the Sun’s zodiacal dust but with a million times greater amounts of dust than the zodiacal dust, and the BD+20 307 particle sizes are typically much smaller than the size of the zodiacal dust particles. The group interprets the BD+20 307 phenomenon as evidence of recent massive and violent collisions of asteroidal-size objects.

Work on projecting the future orbital evolution of objects in the solar system continues. This is an effort to understand the possible connections between orbital dynamics and the evolution of rocky planets in our own solar system, with an eye towards relating such forcing of planetary evolution to the evolution of life. Members of the UCLA team carried out a detailed analysis of numerical simulations of our solar system. They found that chaos in the inner solar system has two sources. While the chaotic interaction between Earth and Mars is the main source of, there is smaller component in the interaction of Venus and Mercury. They note that the system is presently in a transition to a more chaotic state (Figure 1).

Members of the UCLA team completed two studies pertaining to the details of the processes that gave rise to rocks in our solar system. Such studies are useful in the context of astrobiology as the afford comparisons with astronomical observations of nascent solar systems forming around other stars. For example, our team found that the time scale for high-temperature processing of protoplanetary dust was likely to have been on the order of 300,000 years. This span of time can be compared with the lifetime of protoplanetary disks elsewhere in the galaxy (e.g., the Orion nebula). Similarly, members of the team showed this year that photochemistry of the sort that is known to occur in the interstellar medium might also explain the anomalous distribution of the isotopes of oxygen that comprises a first-order characteristic of solar system materials. It may be possible to use these results to constrain the astrophysical environment in which our solar system formed, and thus to make inferences about where other Earth’s might be forming today.

Habitability of planets and their satellites

Detection of small amounts of methane in the Martian atmosphere has been reported now by three different groups. Our team has been engaged in evaluating the likelihood that such a detection is a sign of life on Mars.

Since organisms referred to as methanogens are a primary producer of methane on Earth, the mere presence of methane on Mars begs the question as to whether or not Martian methane might also be biogenic. The logic is that the methane (CH 4 ) molecule can not survive in the thin Martian atmosphere due to the high flux of penetrating ultraviolet light from the Sun, and yet part per billion levels (10 ppb) of the gas are present. One is forced to conclude that the CH 4 is being produced at the present time. However, the methane flux implied by the new measurements is only one-millionth the terrestrial methane flux. This means that the many abiogenic sources of methane on Earth would be sufficient to explain the presence of CH 4 on Mars today.

The UCLA lead team considered the viability of reactions between hydrothermal fluids and rocks deeper in the crust of Mars as potential abiogenic sources of CH 4 . Previous work on the shergottite Martian meteorites demonstrated that the partial pressure of oxygen in the Martian crust was such that carbon dioxide (CO 2 ) in a water-dominated hydrothermal fluid will be converted to CH 4 at temperatures of about 400 °C and less. Phase separation of supercritical water and methane results in methane vapor, which can then diffuse through the crust and reach the atmosphere. The UCLA workers showed that a very small igneous intrusion (~1 km wide x 10 km long) at a depth of 10 km could easily explain a 10 ppb methane fraction in the Martian atmosphere. The implication is that the presence of methane in the Martian atmosphere is most likely a result of the normal physical chemistry associated with reactions between water and rock and can not be taken as evidence for the presence of methanogens, at least not yet.

Earth’s early environment

Our lead team was involved in a study that shows that water was extant very early in Earth history. The work is the latest outcome of an on-going project aimed at reconstructing Earth’s history predating the oldest terrestrial rocks (but not the oldest mineral grains). The workers used the concept of a “geothermometer” (Figure 1) to show that the most ancient mineral grains on Earth, ca. 4.0 to 4.3 billion year old zircons from the Jack Hills of Western Australia , crystallized from granites. The formation of granites of this type requires partial melting of rock in the presence of water. Without the water, the rocks could not form at such low temperatures. The team concludes that the formation of the low-temperature granites during the Hadeon Eon of Earth history (4.5 to 4.0 billion years ago) means that there was a cycle of water-driven weathering and crust formation that resembled that of today. This is an important conclusion in that it implies that conditions during Hadeon time were not so inhospitable to life as previously thought. Is it possible that life on Earth began much sooner than is commonly supposed?

Studies of the nature of the Cretaceous-Tertiary boundary (Tasman Sea) and the Triassic Jurassic boundary ( Nova Scotia ) continued this past year at UCLA. In the latter case the team finds evidence of a small iridium (Ir) anomaly that might be from terrestrial volcanism rather than impact of an asteroid. This is important as there is a long-standing debate as to whether or not unusual levels of volcanic activity or asteroid/comet impacts are responsible for mass extinctions. It would seem both impacts and volcanism might play a role. Work continued on the Permian-Triassic boundary where previous claims of shocked quartz are now disproved, and on impacts in the late Eocene that were caused by bolides from the inner asteroid belt. In October 2004, members of our team organized a field trip to sample the Permian Triassic Boundary at Meishan , China in collaboration with workers at the Nanjing Institute of Paleontology. Samples from this collection will be distributed to an international consortium of research labs to test whether these samples contain evidence of asteroid or comet impact.

Research continued into the evidence for ancient life on Earth. Throughout biologic history, microbial life has been ubiquitous, abundant, metabolically diverse, and for the earliest (Precambrian) seven-eighths of geological time, such microorganisms dominatged.  Understanding of this earliest stage of biologic development has progressed markedly in past decades, but problems in identifying fossilized ancient life remain.  Arguably, foremost among them is the difficulty of unambiguously distinguishing true microbial biologic remnants from non-biologic look-alikes.  This problem was the subject of new work at UCLA this year aimed at correlating "biological morphology" with "biological chemistry", albeit the geochemically altered. The newly installed imaging laboratory at UCLA has now developed two non-destructive, non-intrusive techniques, both new to paleobiology/astrobiology, that can be used toward this end. The techniques are confocal laser optical microsopy and laser Raman spectroscopic imagery. Confocal laser optical microscopy provides means to image in three dimensions at micron-scale the visible characteristics of organic-walled microscopic fossils in situ . Laser-Raman spectroscopic imagery provides means to map in situ and in three dimensions (at micron-scale) (Figure 2) the distribution of the carbonaceous matter that comprises suspected fossils, a technique that also provides salient information regarding the geochemical maturity of such carbonaceous (kerogenous) material.  These new techniques are available for collaborative studies and should be applicable not only to Precambrian specimens, but also to samples returned from elsewhere in the solar system.

Research into the nature of early Earth by the UCLA team this past year included completion of a detailed oxygen and carbon isotopic stratigraphic section of carbonate rocks of marine origin comprising the Precambrian-Cambrian boundary in Siberia. The Siberian platform is one of the few places in the world where the Cambrian section is exceptionally complete and well preserved. This unique section spans one of the most geologically and biologically significant boundaries in Earth’s history, spanning the transition from unfossiliferous to fossil-rich strata; the transition marks the first “radiation” of animal fauna. The isotopic signals, represented by over 2000 carbon and oxygen isotope ratios obtained at the UCLA stable isotope laboratory, reveal well-defined cycles of increasing and decreasing 13 C/ 12 C coincident with the earliest stages of the Cambrian “explosion” of life. Such swings in the isotopic composition of carbon in marine sediments are clear signs of changes in climate and or changes in biological productivity. The pattern of isotopic variability is telling us something significant about the relationship between Earth’s early climate and the evolution of animal life. The challenge remains to unravel what these pronounced signals mean.

Evolution of biological complexity

The UCLA team continues to make good progress towards understanding the evolution of life on Earth. An analyses of the whole genomes of eukaryotes (animals, plants, fungi, and other organisms that consist of large, nucleated cells) and of prokaryotes (single celled organisms lacking nuclei) provided suggests that the eukaryotic genome resulted from a fusion of two diverse prokaryotic genomes, linking at the deepest evolutionary levels prokaryotes and eukaryotes. Said another way, the UCLA team concludes that the tree of life is actually a ring of life.

Collaborators from the UCLA team, the Penn State team, and UC Santa Cruz have entered into an agreement with the Department of Energie’s Joint Genome Institute to sequence five genomes of the genus Pyrobaculum and close relatives. These closely related organisms are extraordinarily diverse in their metabolic repertoire, including many sulfur-based metabolisms, making them an ideal group for the study of the mechanisms and evolution of basic energy metabolisms, including sulfate reduction. Sulfate reduction genes arose early in Earth history, making it more likely that microbial sulfate reduction was an important component of ancient Earth’s geochemical cycles.

Collaboration between the UCLA and Penn State teams on whole genome comparisons and hierarchical classifications continued this year. These workers are preparing a new publication on a novel classification scheme based on measurements of conserved gene order. This broad analysis will address also correlations of nucleotide level versus gene order evolutionary changes across different lineages.

Education and public outreach

Members of the UCLA lead team were engaged in an active EPO program this past year. The Center for the Study of Evolution and the Origin of Life (CSEOL) at UCLA convened an all-campus, free-of-charge, open-to-the public symposium entitled “Astrobiology: Life Among the Stars” in May of this year. Our director of EPO co-hosted a session at the American Geophysical Union Fall Meeting devoted to the subject of diversity and equity in the Earth and space sciences, participated in the NAI — SETI astrobiology summer science experience for teachers, and participated, along with a graduate student, in the Science Study of Navajo Astronomy held on the Navajo Reservation, New Mexico . Our program also conducted a number of class presentations and tours for local K-12 school children dealing with the subject matter of astrobiology. Finally, we are now completing final plans for a lecture series on astrobiology in association with Griffith Observatory.