2000 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 1999 – JUN 2000
Coevolution of Life and Planets
The Kirschvink lab has focused on several aspects of interest to the National Astrobiology Institute during the past 1.5 years, including evaluation and identification of Precambrian biosignatures, testing the Panspermia hypothesis with the Martian Meteorite ALH84001, placing constraints on Life on Europa, assessing effect of the Paleoproterozoic â??Snowball Earth’. Members of the group include Postdoctoral Scholar J.W. Hagadorn, JPL Postdoctoral visitor Eric Gaidos, Graduate Student Benjamin Weiss, and Undergraduate Students Francis Macdonald and Tim Raub.
Biosignatures: Our most important work in this area has been working on the morphology of the fine-grained magnetite in the carbonate blebs of the Martian meteorite ALH84001, in collaboration with Kathy Thomas and Dave McKay of the Johnson Spaceflight Center. 27% of the magnetite crystals are indistinguishable from the magnetite produced by living magnetotactic bacteria. This is the strongest evidence yet for life on Mars, and the combination of 6 biosignatures has no known mechanism form through inorganic processes. Indeed, there are fundamental chemical and physical reasons why inorganic origins are implausible. (Thomas-Keprta, Wentworth et al. 1999; Thomas-Keprta, Bazylinski et al. 2000)
We are also developing two additional techniques for biosignature detection with groups at JPL. These include: (1) an in-situ chemical imaging system (combining AFM laser-ablation chemical spectroscopy) with Greg Bearman at JPL, and (2) a microwave technique for detection of elongate magnetofossils with Sam Kim at JPL.
Panspermia: On a related project spearheaded by Ben Weiss, we have demonstrated that ALH84001 moved from Mars to Earth without ever reaching temperatures of 40 â??C. Hence, this is the first evidence that life can jump between planets. Life on Earth may have evolved first on Mars, then jumped here. (Weiss, Kirschvink et al. 2000; Weiss, Kirschvink et al. 2000)
Life on Europa: Using straightforward arguments concerning redox gradients and the source of oxidants, we have shown that any biosphere on Europa would be severely limited by lack of metabolic energy. Don’t expect fish, but you might find an occasional microorganism (Gaidos et al., 1999).
Snowball Earth: We have discovered that the Kalahari magnanese field in South Africa formed in the immediate aftermath of one of the most severe episodes of global glaciation in Earth history, ~ 70 myr in duration (Kirschvink et al., 2000). We are currently testing hypothesis that the Ongeluk flood basalts (immediately overlying the tillite) may have been triggered by lithospheric contraction produced by the prolonged episode of refrigeration on the continental crust (Raub et al., in prep.).
Nearby Young Solar Analogs: Eric Gaidos has been studying a catalog of young solar-type stars within 25 pc as plausible analogs to the Sun and the Earth’s astrophysical environment during the first 800 Myr of Solar System history. We are carrying out a multi-wavelength (from X-rays to radio waves), multidisciplinary, and collaborative campaign of observations and analysis to study these objects.
Metazoan Radiation & the Cambrian Explosion: For the last year and a half, Whitey Hagadorn has been a Postdoctoral scholar in the Kirschvink laboratory. During this interval, he has been working on a number of projects which relate to Astrobiological research, with primary emphasis on examining the paleobiological record of the terminal Neoproterozoic, as well as the response of metazoans to major perturbations in Earth history, such as the late Neoproterozoic Marinoan glaciations and earliest Cambrian biomineralization event. Some of the current and planned projects are outlined below (#1-4 below), followed by a list of Astrobiology-related papers which he has published or submitted in the last 1.5 years. Whitey’s report follows here:
Current and Planned Projects:
1. Noninvasive 3-D Visualization of Bacteria in Extreme and Precambrian Earth Rocks: A Prelude to Martian Sample Analysis
Collaborators: J. Kirschvink (CIT) K. Nealson, A. Tsapin (JPL),
Questions/Objectives: Employ microscopic computed tomography (microCT) as a primary noninvasive search mechanism for identification of bacteria embedded in rocks. Refine protocols for extracting and rendering three dimensional models of filaments from both matrix-embedded Precambrian samples, and in modern samples bearing endolithic cyanobacteria.
Description: The search for direct evidence of life on other planets and in early Earth history requires analysis of solid objects, such as rock or soil samples. Bacteria from extreme Earth environments (e.g., dry valleys, hydrothermal springs) provide a glimpse of how life might manifest itself on other planets, and fossilized microbiotas from Earth provide a glimpse of how the remnants of such life might be preserved in extraterrestrial samples. Although a variety of geochemical, spectroscopic, mineralogic, and related techniques are being developed to assess extant and fossil life signatures, there are few noninvasive, nondestructive techniques being developed to probe samples and identify areas of potential investigation.
Recent technological advances in microCT technology allow penetration of highly dense samples and identification of features with 5 _m precision, thus providing a means for preliminary scouting of both terrestrial and extraterrestrial samples for morphologic evidence of life. In pilot microCT studies of silicified Neoproterozoic microfossils, lithified microfossils >10 _m in size are clearly visible. Similarly, living endolithic algae, fungi, and lichens are visible in quartzitic samples from Antarctic dry valleys. At present, we plan to write these preliminary results up this summer, and will present our findings at the Fall Geological Society of America meeting.
Given that the resolution levels of microCT will approach 1 _m in coming years, it is logical to develop a set of protocols for using this technique to analyze extraterrestrial rock and soil samples. Archean and Proterozoic microbiota samples and modern endolithic bacterial samples will be analyzed using microCT. In addition to quantification of the location and morphometric characteristics of biotas within each sample, protocols will be developed for isosurface mapping and volume rendering individual fossils. A spectrum of preservational and lithic types will be analyzed in order to identify which sample types are most amenable to these noninvasive scouting techniques, and to provide a noninvasive prelude to subsequent invasive and destructive biological and geochemical analyses.
2. Paleobiology, Paleoecology, and Taphonomy of Neoproterozoic Megafaunas: Morphologic, Microfabric, and Microbial Insights
Collaborators: D. Breen (CIT), B. Waggoner (UCA), J. Nesson (NIH)
Questions/Objectives: Is Ediacaran preservation and ecology tied to microbial binding of siliciclastic substrates? How do preservational variations impact our understanding of their morphology? Do putative metazoan Ediacaran fossils contain a gut and/or coelom? Is the first appearance of metazoans tied to this unique preservational scenario, or is it linked to evolutionary novelty developed in the post-Snowball aftermath?
Description: Preservation of Ediacaran organisms in siliciclastic sediments is hypothesized to have been restricted by microbial mantling of carcasses, coupled with subsequent restriction of pore-water migration within such microbial mat-laden sediments. Because Ediacaran preservation is unlike that of other Phanerozoic or modern environments, numerous difficulties exist in interpreting their paleobiology and paleoecology â?? leading to debate whether some Ediacarans are animals, lichens, and/or constitute their own Kingdom.
To test the hypothesis that preservation of Ediacaran faunas is mediated by microbial mantling, the first phase of this project will utilize detailed microfabric, geochemical, SEM, and x-radiographic analyses to identify diagnostic microbial structures (e.g., wrinkle structures, “sponge sand” textures, biomarker, _13Corg signatures) in ancient Ediacaran-bearing samples. Phase two of this project will involve CT-scanning of Ediacaran fossils from both fine- and coarse-grained deposits to obtain quantitative morphologic characteristics for each taxon. Volumized density isosurfaces will be rendered to evaluate postburial morphology of matrix-embedded samples. These volumes will provide an initial datum for retrodeformation of fossil models into possible preburial morphologies. Phase three will involve evaluation of density and microfabric variations within Ediacaran fossils preserved in fine-grained strata â?? in order to identify internal features within the fossils which might provide clues about their anatomy and placement within existing clades (e.g., subtle variations in composition, porosity, and sedimentologic features which may be associated with preferential decay of soft tissue, including coelomic cavities).
To date, I have been trained in operation of medical CT equipment, and worked to streamline data transfer from medical formatting to cross-platform formats. At present, I am learning to utilize volume rendering and isosurface mapping software. We have pilot data sets for a variety of Ediacaran biotas and faunas from other fossil lagerstätten â?? comprising a range in preservational and lithologic modes. In several cases, we have identified concealed features which have the potential to elucidate the taxonomic affinity of some of these organisms. For example, analyses of several discoidal forms (e.g., Cyclomedusa, Nimbia, Spriggia, Tirasiana) quickly allows separation of discoids into paleobiologically meaningful groups who share morphologic syapamorphies, such as presence of a stalk, or an internal cavity.
3. Significance, Taxonomy, and Biomineralization of Terminal Neoproterozoicâ??Lower
Cambrian Conical Fossils
Collaborators: J. Kirschvink (CIT), W. Fritz (GSC), J. Hollingsworth (Union Carbide), F. Corsetti (UCSB)
Questions/Objectives: Do problematic conical fossil concentrations (e.g., Cloudina coquinas) represent the earliest “disaster taxa”? Are these morphologically similar, but simple, faunas related? How did biomineralization develop in the earliest skeletal fossils? Is the onset of biomineralization related to post-“Snowball Earth” changes in ocean chemistry, and/or exaptation of an ancestral biomineral system?
Description: Fossil concentrations (or “shell beds”) dominated by problematic conical taxa (e.g., Cloudina, Volborthella, Salterella, Orthothecida) are a relatively common type of shell bed in Terminal Neoproterozoicâ??Lower Cambrian strata, but are particularly extensive in strata of the southwestern Great Basin and northwestern Mexico. Because most of these fossil concentrations are intimately associated with hiatal surfaces and trilobite extinction events: i) these conical fossil concentrations are hypothesized to represent the earliest opportunistic “disaster taxa”; and ii) coeval Cloudina beds of varying mineralogy may provide insights about the development of metazoan biomineralization.
i) To test the “conical fossils as disaster taxa” hypothesis, the paleoenvironmental distribution, mode of deposition, and stratigraphic position of these conical fossil deposits will be characterized. Conical fossil concentrations will be examined in detail in the field using standard shell-bed analytic, sequence stratigraphic, and biostratigraphic techniques to determine: i) if they reflect opportunistic disaster taxa; ii) what factors might account for their abundance (i.e., eustatic, geochemical, predation factors); iii) what ecologic niches might be compatible with their rapid appearance; and iv) if/how such horizons may be utilized as regional biostratigraphic cues in (4) below.
ii) Based on the best preserved silicified and phosphatized samples, petrographic, microCT, microprobe and geochemical techniques will be used to identify the locus and nature of biomineralization within “protoconches” of Cloudina, and to evaluate the relationship between variations in skeletal mineralogy observed within coeval cloudiniid concentrations, regional patterns in oceanic 87Sr/86Sr and _13Ccarb, and other biomineralization events. Mineralogic, morphologic, and related contextual information will provide a logical first step towards identifying characters to evaluate the systematics of these conical fossil taxa, and their role in the development of biomineralization within the Metazoa.
To date, we have identified and collected pilot samples from most of the major conical fossil horizons in California, Nevada, and Mexico. A rough biostratigraphic framework has been constructed to evaluate the synchroneity of putative coeval conical fossil concentrations. MicroCT analyses of silicified cloudiniids have yielded the best morphometric information to date, and petrographic analysis of these pilot samples will occur this summer.
4. The Terminal Proterozoicâ??Cambrian Transition: Southwestern North America
Collaborators: J. Kirschvink (CIT), B. Wernicke (CIT), F. Corsetti (UCSB), J. Stewart (USGS), R. Amaya Martinez (UNAM)
Questions/Objectives: Create a 20 Ma-precision integrated geochronologic, biostratigraphic, paleomagnetic, lithostratigraphic, and geochemical framework for Neoproterozoic strata of southwestern North America. Based on this framework: Are strata of the Sonoran province correlative to Precambrian-Cambrian strata of the southwestern US? Do glaciogenic diamictites and associated “cap carbonates” trigger the onset of metazoan evolution? Is the appearance of metazoans really linked to rapid inertial interchange (true polar wander)?
Description: One of the most intriguing areas of modern stratigraphic research centers on the sudden diversification of multicellular life and its relationship to global environmental changes at the end of the Proterozoic. Debate persists regarding the timing and number of glaciations during this interval, global changes in ocean chemistry reflected in isotopic excursions, the timing and nature of true polar wander, and how these events relate to the Cambrian radiation and its precursors.
Southwestern North America contains a well-exposed, relatively complete Neoproterozoic-Cambrian succession that is well characterized lithostratigraphically. It contains well identified glacial intervals, abundant carbonate for chemostratigraphic analysis, high potential for biostratigraphic preservation, locally well-preserved Proterozoic magnetizations, and good potential for chronostratigraphic control. Given recent advances in dating diagenetic minerals in non-volcanic clastic strata, the succession therefore has strong potential for constraining the total number of terminal Proterozoic glacial events (and associated “cap” carbonates), for identifying their relationship to isotopic excursions, and for assessing any relationship between these events and the diversification of phytoplanktic and/or multicellular life.
To evaluate the relationship between these events, we will establish an integrated bio-, chrono-, chemo-, and magnetostratigraphic framework for Neoproterozoic to Lower Cambrian strata in southwestern North America. This framework will link the two main regional Proterozoic-Cambrian successions, including strata in the White-Inyo/Death Valley/Mojave region, and strata in the Sonora region. My contribution to this research effort will be constructing the microbiota and macrofossil biostratigraphic framework, analyzing diagenetic mineral assemblages to construct a geochronologic framework, and evaluating the relationship between hypothesized snowball and true polar wander events to biotic shifts.
PROJECT MEMBERS:Joseph Kirschvink
RELATED OBJECTIVES:Objective 6.0
Define how ecophysiological processes structure microbial communities, influence their adaptation and evolution, and affect their detection on other planets.
Identify the environmental limits for life by examining biological adaptations to extremes in environmental conditions.
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
Determine the presence of life's chemical precursors and potential habitats for life in the outer solar system.
Understand the natural processes by which life can migrate from one world to another. Are we alone in the Universe?
Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars, especially the habitable ones.
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Determine the resilience of local and global ecosystems through their response to natural and human-induced disturbances.
Refine planetary protection guidelines and develop protection technology for human and robotic missions.