Microbial Biosignatures in Ocean Basalts
EMSL Project ID
3391
Abstract
Substantial evidence supports the view that microorganisms can effect widespread geochemical changes in the lithosphere. The alteration of basalts to palagonite was once viewed as a chemical process (Crovisier 1983; Staudigel 1983; Thorseth 1991); however, the possibility that microorganisms participate in this process, and perhaps accelerate it, has emerged as an important but unresolved scientific question. There is every reason to think that microorganisms might be involved in the alteration of the igneous crust, because this process occurs on a vast scale at habitable temperatures in aqueous environments and the reaction releases huge amounts of chemical energy. On the other hand, it is uncertain which redox couples might fuel such a lithospheric ecosystem, because (1) known biochemistry presents numerous possibilities, and the system itself has substantial chemical clines on macroscales, and probably on microscales, which might make various of these pathways possible at different times and places, and (2) it is reasonable to suspect that unknown biochemical processes that involve solid state chemical transitions at interfaces might occur.Evidence that microorganisms catalyze alteration processes, which we will call the microbial hypothesis, would precipitate a fundamental shift in scientific perceptions of crustal chemistry. To date, there is no conclusive evidence either in favor of the microbial hypothesis, or ruling it out. Most studies, including ours, have focused on documenting phenomena of apparent microbial origin - characteristic textures, anomalies in elemental composition (C, N and P), organic matter, and nucleic acids - at the alteration front in rocks recovered by the Ocean Drilling Program (ODP). These studies have made it clear that these phenomena are widespread in basaltic glasses collected at temperatures conducive to life, but have not pinned down the processes that are responsible for these features. Although any microbial life in the lithosphere is interesting, there is a big difference between biofilms being present (at this point it would be a surprise if they were not) and active microbial participation in alteration chemistry. Interest in the latter possibility (the microbial hypothesis) is quite justified because the phenomena we describe (e.g. carbon maxima from electron microprobe measurements, DNA staining and textural features interpreted as cellular debris) are found exactly at the microscale site of glass alteration (the alteration front).
Project Details
Project type
Exploratory Research
Start Date
2003-08-15
End Date
2004-08-16
Status
Closed
Released Data Link
Team
Principal Investigator
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