2003 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 2002 – JUN 2003
0 Field Sites
- ALH84001: We have developed a successful detection strategy based on microwave ferromagnetic resonance for the identification of bacterial magnetofossils. On a series of control sediments that have been examined extensively with high-resolution transmission electron microscopy (HRTEM), this technique is able to rapidly distinguish those that do and do not contain magnetofossils. The basic principle exploits the magnetic anisotropy produced by linear chains of single-domain magnetite crystals, such as those produced intracellularly by the magnetotactic bacteria. Initial results on carbonate blebs from Martian meteorite ALH84001 are not incompatible with the presence of magnetofossils (Weiss et al., in review). Work is in progress to develop this procedure into a portable instrument that could be used in the field for magnetofossil and paleomagnetic studies, as well as possibly for eventual inclusion on a Martian lander.
- Microbial Genetics: Our whole-genomic analysis of the nearly complete genomic sequence of two magnetotactic bacteria argues against lateral gene transfer as the acquisition mechanism for magnetotaxis (Nash et al., in review). Numerous clusters of conserved genes are at scattered locations around the physical genome in these two organisms. Magnetotaxis appears to have arisen very close to the root of the bacterial Domain, if not earlier. More recently, in samples of pure magnetotactic bacteria from the anoxic, hypersaline, hyperalkaline sediments from Mono Lake, California, we have detected two organisms with Archaebacterial ribosomal ribonucleic acid (rRNA). This is the first report of magnetotactic Archaebacteria and shows that magnetotaxis is a trait common to all three domains of life, further suggesting that the last common ancestor of all living organisms may have been magnetotactic. This is not inconsistent with the presence of putative magnetofossils in the 4 billion year old ALH 84001 carbonate globules from Mars and 2 billion year old terrestrial magnetofossils.
- The Paleoproterozoic Snowball Earth and the Great Oxygenation Event: A detailed sedimentological and paleomagnetic investigation of the glaciogenic Huronian sediments in the Sudbury area of Canada has demonstrated that low-latitude magnetizations once thought to be primary, and hence suggestive of low-latitude glaciation, are in fact secondary magnetic overprints that fail a small-scale paleomagnetic fold test (Hilburn et al., 2002). A detailed comparison of these units with those in South Africa (for which the youngest glacial event, the Makganyene diamictite, is low-latitude) suggests that all 3 Huronian glacial advances are older than the Makganyene event. Hence, there seems to have been only one clear Paleoproterozoic Snowball Earth episode. We have not been able to disprove the hypothesis that this event was triggered by the geologically sudden collapse of a methane-greenhouse atmosphere, perhaps in response to the evolution of O2-releasing cyanobacteria. The concept that a discrete evolutionary event (like the evolution of O2-releasing photosynthesis) could cause the destruction of an entire planetary ecosystem is a rather sobering thought.
PROJECT INVESTIGATORS:Kenneth Nealson
Project InvestigatorJoseph Kirschvink
PROJECT MEMBERS:Francis Macdonald
RELATED OBJECTIVES:Objective 1.1
Models of formation and evolution of habitable planets
Sources of prebiotic materials and catalysts
Origins of energy transduction
Earth's early biosphere
Foundations of complex life
Effects of extraterrestrial events upon the biosphere
Environment-dependent, molecular evolution in microorganisms
Environmental changes and the cycling of elements by the biota, communities, and ecosystems
Biosignatures to be sought in Solar System materials