2001 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 2000 – JUN 2001
Fe Isotope Biosignatures Group
Fe Isotope Biosignatures Group (dm)
Our major effort this year focused on a) bringing new instrumentation on line for ultra-high precision Fe isotope measurements on very small samples, b) continuing Fe isotope studies of natural samples that may have a biologic origin, and c) experimental determination of Fe isotope fractionation in minerals and fluids. A next-generation multi-collector ICP-MS was installed in a new clean lab, in part funded by NAI, and this instrument produces an unprecedented level of precision (+/- 0.05 per mil) for Fe isotope analysis on very small samples (~ 100 ng). Using our new instrumentation, we completed a survey of late Archean Banded Iron Formations, where up to 3 per mil variation in 56Fe/54Fe ratios were found, making it clear that Fe isotope variations can be preserved in the ancient sedimentary record. Work on determining Fe isotope fractionation in the lab led to the discovery of large (2.7 per mil) isotopic fractionation between Fe(III) and Fe(II) in dilute aqueous solution. Work on the hematite-Fe(III) system showed that although kinetic isotope effects can occur during rapid precipitation of hematite from solution, equilibrium isotope fractionation in this system appears to be minimal. In summary, our results demonstrated, for the first time, that Fe isotope anomalies appear to be restricted to low-temperature, aqueous environments, providing a powerful biosignature for detecting conditions on a planet that were favorable for life. In terms of accomplishments related to our original goals, installation and development of our new instrumentation progressed much faster than we had anticipated. The Fe isotope variations we documented in Banded Iron Formations were much larger than we originally thought, as were the isotopic fractionations among aqueous species. These discoveries have clearly influenced our plans for the coming year.
PROJECT MEMBERS:Clark Johnson
RELATED OBJECTIVES:Objective 3.0
Replicating, catalytic systems capable of evolution, and construct laboratory models of metabolism in primitive living systems.
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars, especially the habitable ones.
Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet.