2008 Annual Science Report
University of Colorado, Boulder Reporting | JUL 2007 – JUN 2008
Understanding the Microbial Ecology of Geologically-Based Chemolithoautotrophic Communities
The objective of this project is to investigate the potential for geologic systems to support the production of biomass by chemosynthetic microorganisms that use inorganic chemical reactions rather than sunlight as a source of metabolic energy. The research focuses on hydrothermal and subsurface environments, where reaction of water with rocks produces sources of chemical energy like those that might have occurred on the early Earth, or that might occur now on other planetary bodies like Mars and Europa. Numerical geochemical models of fluid-rock interaction have been developed to understand the types and amounts of chemical energy that are generated in modern geologic environments, and to explore how these chemical energy sources may have differed under the different conditions present on the early Earth or in extraterrestrial environments.
The focus of this project is an evaluation of the amounts and types of chemical energy that are made available to support chemosynthetic microbial communities by fluid-rock interactions in ultramafic-hosted submarine hydrothermal systems. Chemosynthetic microbial communities in these systems utilize dissolved hydrogen and methane produced by the reaction of heated seawater with the ultramafic rocks as their metabolic energy sources. Geochemical models developed for this project indicate that the total amount of chemical energy available to support chemosynthetic organisms in ultramafic hydrothermal systems is comparable to, or greater than, that available in the better-studied basalt-hosted systems, although the dominant forms of chemical energy are substantially different. This results of this research were published in December in the journal Astrobiology. Since hydrogen is the main source of chemical energy to support the microbial community in these systems, additional numerical geochemical models have been developed to investigate the chemical reactions responsible for hydrogen production during alteration of ultramafic rocks (serpentinization). Results of these models indicate that temperature and the partitioning of iron among alteration minerals exert the dominant controls on the amount of hydrogen produced, with hydrogen production peaking during hydrothermal alteration at temperatures around 300°C and falling off steeply at both higher and lower temperatures. This result suggests that the most productive microbial communities should occur in hydrothermal systems with temperatures around 300°C, but systems in this temperature range have so far not been discovered on the seafloor. A paper describing these models is currently in review at Geochimica et Cosmochimica Acta.
PROJECT INVESTIGATORS:Thomas McCollom
RELATED OBJECTIVES:Objective 2.1
Earth's early biosphere