2002 Annual Science Report
University of California, Los Angeles Reporting | JUL 2001 – JUN 2002
Geobiology and Geochemistry of Early Earth and Mars
Ion microprobe analyses carried out in the Keck Center for Isotope Geochemistry
(T. Mark Harrison and Kevin D. McKeegan, Directors) continue to provide highest
quality data for studies of the early Earth and Mars. Building on a pilot study
aimed at finding the oldest terrestrial materials (Mojzsis et al., 2001), some
5,300 individual zircon crystals from the Jack Hills conglomerate in Western Australia
have now been dated. Two percent of these are 4 billion years old or older, thus
providing a source for geochemical evidence that can be used to constrain models
of the Earths earliest atmosphere and hydrosphere.
Collaborator James Farquhars discovery of substantial mass-independent
fractionations of sulfur isotopes in rocks older than about 2.3 billion years
(Farquhar et al., 2000) and his demonstration that these effects are produced
in gas-phase reactions (Farquhar et al., 2001) implicate the atmosphere in sulfur
cycling on the early Earth (Runnegar et al., submitted).
Understanding these mass-independent isotopic effects requires knowledge of
a simpler and better-understood modern system. UCLA photochemist James Lyons has
developed a quantitative model for the behavior of mass-independently fractionated
oxygen in the lower atmosphere and the stratosphere (Lyons, 2001). This work will
lead to models and experiments aimed at a better understanding of the more complex
The possibility that organic matter on the early Earth was made inorganically is being investigated experimentally in a cross-team collaboration with the Penn State team (Craig E. Manning, Tracey Herrera, Christopher H. House). They are also exploring the interaction of microbes with olivine and other mineral substrates. Preliminary results indicate that microbial activity greatly increases certain inorganic reactions by using reaction products for metabolic purposes.
In a remarkable example of the emergent properties of the NASA Astrobiology
Institute, involving both cross-team and cross-discipline collaborations, Victoria
J. Orphan and her coauthors provided stunning isotopic and phylogenetic evidence
for the anaerobic use of methane by highly organized microbial consortia composed
of sulfate-reducing bacteria and methane-consuming archaea (Orphan et al., 2001;
Zimmer, 2001). In a follow-up study (Orphan et al., 2002), they used the same
techniques to expose the complexity of microbial communities involved in methane
oxidation in an anoxic cold seep environment.
PROJECT MEMBERS:Bruce Runnegar
T. Mark Harrison
M. Indira Venkatesan
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
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.