2009 Annual Science Report
VPL at University of Washington Reporting | JUL 2008 – AUG 2009
Understanding Past Earth Environments
This project examines the evolution of the Earth over time. This year we examined and expanded the geological record of Earth’s history, and ran models to help interpret those data. Models were also used to simulate what the early Earth would look like if viewed remotely through a telescope similar to NASA’s Terrestrial Planet Finder mission concept. We focused our efforts on the Earth as it existed in prior to and during the rise of atmospheric oxygen 2.4 billion years ago, as this was one of the most dramatic and important events in the evolution of the Earth and its inhabitants.
Chemical evolution of the early Earth:
Investigations of early biogeochemical cycling and microbial evolution included nitrogen isotopic studies of latest Archean drill-core which showed that, as a result of a pre-Great Oxidation Event “whiff” of atmospheric oxygen, an aerobic nitrogen cycle including nitrification and denitrification existed well before previously recognized. Because marine nitrification is, as far as we known, overwhelmingly performed by only two groups of microbes on terminal branches of the Tree of Life, this implies that microbial macro-evolution was largely complete by the end of the Archean. (Garvin et al., 2009). Studies of early Archean sediments confirmed the very early evolution of microbial sulfate reduction but failed to find any evidence for sulfur disproportionation (Shen, et al., 2009). Organic geochemistry of earliest Paleoproterozoic oily fluid inclusions showed that biomarker molecules indicated the earlier evolution of oxygenic photosynthesis and eukaryotic organisms (Buick et al., 2009). Thus, three major metabolisms and corresponding redox-sensitive biogeochemical cycles were extant before the atmosphere became permanently oxygenated.
We also contributed to a report of a radical decline in the amount of Ni in Proterozoic oceans, as measured by the amount of nickel precipitated in BIFs. Under low-Ni conditions, methanogens are put at a competitive disadvantage and less methane is emitted into the atmosphere. The Ni decline was attributed to the cooling of the Earth, and is a demonstration a geological influence on biological evolution.
In addition to our work on Archean biogeochemistry, we have also made progress in our ability to measure the atmospheric surface pressure of the Archean.
Modeling Archean Surface Environments:
Model improvements were made to our 1-D photochemical code so that it can simulate the transition from anoxic to oxic conditions; this also allows us to model a wider variety of expolanets. Our climate code has been improved through the addition of new greenhouse gases and particle species. Our atmospheric escape code now includes multiple species (Feng et al., 2008).
Models were used to simulate Archean climate (Haqq-Misra, et al., 2008, Figure 1 below) and produce spectra of Archean-like planets. These spectra included the effects of organic Sulfur species that may be signatures of anoxic biospheres (Domagal-Goldman et al., 2009; see also VPL Project Report on Detectability of Biosignatures).
The NASA Ocean Biogechemical Model (NOBM) was run with cyanobacteria acting as the only photosynthetic group in the oceans. Total primary production decreased about 19% from the standard configuration because cyanobacteria are relatively slow growers compared to modern phytoplankton. The reduced growth led to less efficient uptake, resulting in increases in nitrate and dissolved iron in the surface ocean.
Finally, we have improved our ability to probe the Earth’s oceanic redox history with applied quantum mechanical predictions of Fe isotope fractionation from redox reactions (Domagal-Goldman, et al., 2008 and Domagal-Goldman and Kubicki, 2009).
PROJECT INVESTIGATORS:Roger Buick
Project InvestigatorDavid Catling
Co-InvestigatorDavid Des Marais
Doctoral StudentTyler Robinson
Doctoral StudentSanjoy Som
Doctoral StudentJonathan Breiner
Undergraduate StudentNoe Khalfa
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Earth's early biosphere.
Production of complex life.
Effects of extraterrestrial events upon the biosphere
Environment-dependent, molecular evolution in microorganisms
Co-evolution of microbial communities
Biochemical adaptation to extreme environments
Effects of environmental changes on microbial ecosystems