Exobiology and Evolutionary Biology

PI: Everett Gibson

The goal of this proposal is to establish new biosignatures of well preserved, Precambrian organic microfossils that can serve as a baseline for interpreting less well preserved organic fragments in either terrestrial or extraterrestrial samples. The work will be based primarily on the new technology of NanoSIMS which provides sub-micron scale elemental, isotopic, and structural information. We will focus on microfossils ranging in age from 0.8 to ~2 Ga and representing a variety of depositional settings, all of which are analogs for environments in which life may have developed on Mars. Comparisons will be made with carbonaceous residues in hydrothermal veins and with published NanoSIMS analyses of non-biogenic, organic inclusions in carbonaceous chondrites. From these data, a set of criteria will be developed for recognizing indigenous, biogenic signatures and differentiating them from non-biogenic constituents or post-depositional, biological contaminants. We will also apply NanoSIMS to some of the oldest potential microfossils on Earth and will use the criteria developed to evaluate the significance of those structures and of reduced carbon in the martian meteorite, Nakhla. Key to this proposal is that the microfossils to be used as a baseline are of undisputed biogenicity. This provides the opportunity to determine characteristics that may be diagnostic of biologically-derived organic matter.
Dr. Oehler and colleagues have published the first in-depth NanoSIMS analysis of Proterozoic microbial remains (Oehler et al., 2006a-c) and have initiated NanoSIMS study of Archean structures (Oehler et al., 2007b). Results are suggestive of a new category of biosignatures and may provide a means for recognizing post-depositional contaminants. Our hope is that this research will lead to new insight into the earliest evolution of life on Earth as well as to strategies that can be used in the search for remnants of life on other planets and in meteorites.