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Habitability, Life Detection, and the Signatures of Life on the Terrestrial Planets

The research of the University of Wisconsin team is fundamentally built around a broad interpretation of Life Detection, which includes not only detection of the organic signatures of life in modern (and ancient) environments, on Earth or other planetary bodies, but also the inorganic signatures of life, which may have the greatest fidelity over billion-year timescales and complex geologic histories. Recognizing that development of robust biosignatures is challenging, they have designed a research plan that back-stops development of the Signatures of Life with proxies that simultaneously inform us about the Habitability of ancient environments on Earth and other planetary bodies, including Mars.

Distinctive features of their research program are integration of biologic and abiologic studies and an emphasis on state-of-the-art in situ, micron-scale chemical and isotopic analysis. The three research components of this team’s program are inter-connected both between projects within a section, as well as across sections.

1. Developing Methods for Life Detection. This component of the Wisconsin team’s research has three objectives: a) Determine biomarker stability in space environments, providing constraints on delivery of organics to early planets, and organic survival over geologic time; b) Calibrate the extent to which biomolecules are retained on minerals, which poses a significant, potential obstacle to successful life detection on planetary bodies; and c) Determine the relations between microbial species, biomarkers, and fluid and mineral geochemistry in modern volcanic hydrothermal systems, providing a view of microbial iron-redox systems on early Earth or Mars.

2. Biosignatures: Developing the Tools for Detection of Ancient Life and Determining Paleoenvironments. There are six research objectives under this component of their research: a) Determine the isotopic fractionations of Mg, Si, and Fe during clay formation, which will constrain weathering and fluid chemistry of early Earth and Mars; b) Understand microbial iron redox cycling of clays and its relation to biomarker binding to clays, as well as any unique isotopic biosignatures; c) Develop an understanding of Si, Fe, and Mo isotope fractionations associated with Fe-Si oxides, which promises to provide a proxy for ancient atmospheric conditions and biological activity; d) Calibrate the chemical and C, O, Mg, and Mo isotope compositions of carbonates as functions of temperature and atmospheric O2 and CO2, to allow use in the ancient rock record; e) Understand the relations between microbial sulfate- and iron-reduction and their signatures in carbonates; and f) Determine the role of organic substances in determining compositions of carbonates.

3. Life Detection in the Ancient Terrestrial Rock Record. This component of their research is organized under seven objectives: a) Determine the origin of the large changes in C, S, and Fe isotope compositions in Neoarchean rocks prior to Paleoproterozoic oxygenation of the environment, and how this fits with the Fe-C-S redox cycles; b) Extend studies of redox cycling and atmospheric evolution back to the Mesoarchean, with a focus on the glacial-interglacial periods and possible roles for methane and oxygen in the atmosphere, as related to microbial evolution; c) Address long-standing controversies of the Paleoarchean, back to 3.5 Ga, in terms of atmospheric conditions and the nature of photosynthesis, including application of multiple isotopic tracers and geochronology on minerals suggested to reflect early oxidation; d) Determine the magnitude of extraterrestrial impacts in the early Earth, and their potential effects on a very early biosphere, through studies of shocked detrital zircons; e) Develop new insights into microbial ecology through studies of Proterozoic microfossils from deep- and shallow-water environments, coupled to in situ C isotope analyses; f) Calibrate the relations between molecular biomarkers and in situ C, S, and Fe isotope measurements of organic matter and pyrite, to better understand the Fe-C-S redox cycle; and g) Apply in situ C isotopes to Paleoarchean microfossils to determine the biogenicity of the oldest putative microfossils and the C cycle in the earliest Earth.