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Executive Summary

Executive Summary — URI (dm)

A better understanding of the Earth’s deep biosphere is essential because it can serve as a model for life on other planets and it is a critical component of the Earth’s biogeochemical cycles. This research is aimed at gaining a fundamental understanding of the life in deeply buried marine sediments. We are undertaking an interdisciplinary set of projects that takes advantage of our considerable expertise in marine sedimentary microbiology, sedimentary biogeochemistry and deep ocean drilling. Our objectives are to understand the subsurface microbial ecosystems of marine sediments, their role in Earth’s biogeochemical cycles, and their relevance to the search for life on other planets. We focus on three major projects.

The first project explores the taxonomic composition, metabolic activity and geochemical consequences of buried microbial ecosystems in marine sediments with widely different physical and chemical characteristics Environments include hot, deeply buried anoxic sediments where life may exist independently of the photosynthesis-based ecosystem at Earth’s surface, and old, deeply buried sediments where life may be limited by the availability of electron donors or key nutrients. The ecosystems of such subsurface habitats are potentially representative of the ecosystems that may exist on other planets.

The second project documents the nature, extent and perturbation-sensitivity of microbial activity in marine sediments and the effect of that activity on Earth’s biogeochemical cycles of various chemical species, particularly sulfate and methane. Sulfate, the second most abundant anion in seawater, is the dominant terminal electron acceptor in marine sediments. Methane is climatically active and marine methane deposits comprise the largest untapped hydrocarbon reservoir on Earth. The biogeochemical cycles of these and other chemical species are potentially sensitive to centennial to millenial changes in Earth’s surface temperatures, nutrient fluxes to the ocean, and the structure of marine ecosystems.

The third project focuses on identifying signatures of present and past microbial processes in Earth’s subsurface as a guide to predicting such signatures in extraterrestrial subsurface environments. The molecular-isotopic based data that will be generated as part of this project will complement the objectives of the first two projects. For example, the study of biomarkers produced by deeply buried methanotrophic microbes give us an indication of both past and present activity of this specific taxonomic group.

We have already obtained extensive sample sets from deep Pacific drill-holes for analysis. We developed procedures for identifying contamination of samples, spearheaded the drive to instrument a microbiology laboratory on the Ocean Drilling Program (ODP) drill-ship JOIDES Resolution, and compiled relevant global geochemical and physical databases. We will participate in the first ODP Leg (Leg 201) dedicated to Subsurface Biosphere research scheduled for 2002. These and other developments provide the framework for collecting, analyzing and interpreting microbiological, biogeochemical and physical data from a wide range of deep subsurface samples. This framework leaves us poised to greatly advance Subsurface Biosphere objectives.

Our approach is fundamentally interdisciplinary and we will use advanced techniques from various fields, including microbiology, molecular biology, organic and inorganic biogeochemistry, isotope geochemistry, large data set integration and computational modeling. The work will be field-, laboratory-, and model-based.