2009 Annual Science Report

VPL at University of Washington Reporting  |  JUL 2008 – AUG 2009

Understanding Past Earth Environments

Project Summary

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.

4 Institutions
3 Teams
20 Publications
0 Field Sites
Field Sites

Project Progress

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).

This figure shows predicted surface temperatures from our climate model (Haqq-Misra et al., 2008) for atmospheres similar to the one thought to have existed on the early (Archean) Earth. These atmospheres are low in O2, but high in the greenhouse gases carbon dioxide (CO2), methane (CH4), and ethane (C2H6). They also have organic hazes that impart a cooling effect on the climate through absorption and reflection of incoming solar radiation. We show predicted surface temperatures (y-axis) for a given CO2 pressure (x-axis) and CH4 concentration (solid lines). The C2H6 and organic haze concentrations are a function of the concentrations of CO2 and CH4, and water concentrations are a function of the temperature of the atmosphere. Also shown on this figure are two dashed lines, representing limits on temperature and CO2 from geological data. Because there are not any known global “snowball Earth” glaciations prior to the rise of O2, the average surface temperature must have been above the freezing point of water (horizontal dashed line). We also have an upper limit on CO2 at various temperatures from paleosol data (diagonal dashed line). According to these interpretations of the rock record, the early Earth should be plotted above and to the left of these two lines; we have no model runs consistent with this scenario. However, the paleosol limit is dependent on the paleolatitude of the samples, which is poorly constrained. We account for this uncertainty by showing the “harder” limit at ~0.03 bars of CO2 (arrow at top of diagram). Our model is consistent with these higher CO2 concentrations, as there are a number of simulations that satisfy both this constraint and that on average surface temperatures.

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).

    Roger Buick Roger Buick
    Project Investigator
    David Catling David Catling
    David Des Marais David Des Marais
    Watson Gregg
    James Kasting James Kasting
    Victoria Meadows Victoria Meadows
    Yuk Yung Yuk Yung
    Tori Hoehler Tori Hoehler
    Kevin Zahnle Kevin Zahnle
    Mark Claire Mark Claire
    Feng Tian Feng Tian
    Jacob Haqq-Misra Jacob Haqq-Misra
    Doctoral Student
    Tyler Robinson Tyler Robinson
    Doctoral Student
    Sanjoy Som Sanjoy Som
    Doctoral Student
    Jonathan Breiner
    Undergraduate Student
    Noe Khalfa
    Undergraduate Student
    Objective 1.1
    Formation and evolution of habitable planets.

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets.

    Objective 2.1
    Mars exploration.

    Objective 4.1
    Earth's early biosphere.

    Objective 4.2
    Production of complex life.

    Objective 4.3
    Effects of extraterrestrial events upon the biosphere

    Objective 5.1
    Environment-dependent, molecular evolution in microorganisms

    Objective 5.2
    Co-evolution of microbial communities

    Objective 5.3
    Biochemical adaptation to extreme environments

    Objective 6.1
    Effects of environmental changes on microbial ecosystems