2002 Annual Science Report
Pennsylvania State University Reporting | JUL 2001 – JUN 2002
Evolution of Atmospheric O2, Climate, and Biosphere - Hiroshi Ohmoto
We have continued to accumulate a variety of geochemical evidence in Precambrian rocks suggesting the atmosphere and oceans became oxygenated and the oceans and land were colonized by diverse organisms by 3.2 billion years ago. This date is at least 1 billion years earlier than most geoscientists have accepted. The investigated rock types include: (a) marine shales and greywackes; (b) paleosols; (c) red beds; (d) banded iron formations; (e) ores (volcanogenic massive sulfides, uraninite); and (f) igneous rocks (volcanics and plutonics). These rocks range from 3.4 to 1.8 billion years in age, and they were systematically collected from the Kaapvaal Craton in South Africa, the Pilbara-Hamersley district in Australia, the Abitibi greenstone belt in Canada, and the Lake Superior district in Canada/USA. The types of geochemical investigations have included: (a) organic geochemistry of organic matter (carbon isotopes, C/P/N/H ratios, C content); (b) Fe geochemistry (Fe/Al, Fe/Ti, Fe3+/Fe2+); (c) sulfur geochemistry (sulfur isotopes, S/C/Fe ratio, S content); (d) rare earth element geochemistry (Ce anomaly); and (e) trace element geochemistry (Mo, U, V, etc).
We have conducted laboratory experiments to determine the dissolution rates of some important redox-sensitive minerals (i.e., uraninite and pyrite) as a function of O2 content and pH of solutions. These data have become essential in relating the geochemical data on natural rocks (see above) to the atmospheric O2 level.
Based on the analyses of laboratory data on the kinetics of oxidation of organic matter and of the carbon contents of marine sediments, we have established a quantitative model for the geochemical cycle of oxygen. We have suggested that the atmospheric O2 level has been maintained within ±50% of the present level since the emergence of oxygenic photosynthesis by two major negative feedback mechanisms. One is an increase in the burial flux of organic matter in marine sediments with decreasing pO2, and the other is a decrease in the O2 consumption flux during soil formation with decreasing pO2.
PROJECT MEMBERS:Hiroshi Ohmoto
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Develop and test plausible pathways by which ancient counterparts of membrane systems, proteins and nucleic acids were synthesized from simpler precursors and assembled into protocells.
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Define how ecophysiological processes structure microbial communities, influence their adaptation and evolution, and affect their detection on other planets.
Identify the environmental limits for life by examining biological adaptations to extremes in environmental conditions.
Understand the natural processes by which life can migrate from one world to another. Are we alone in the Universe?
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Determine the resilience of local and global ecosystems through their response to natural and human-induced disturbances.
Model the future habitability of Earth by examining the interactions between the biosphere and the chemistry and radiation balance of the atmosphere.