Biology
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53d..02m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53D-02
Biology
0419 Biomineralization, 0424 Biosignatures And Proxies, 0448 Geomicrobiology, 0456 Life In Extreme Environments, 0463 Microbe/Mineral Interactions
Scientific paper
Ca carbonate minerals, such as calcite or aragonite, are known to precipitate by both abiologically and biologically produced processes. The abundant sedimentary mineral dolomite (CaMgCO3), however, precipitates exclusively as a microbial induced product under Earth surface conditions. Thus, the study of microbial dolomite precipitation in natural environments and laboratory culture experiments provides the potential to calibrate and evaluate the range of microbial biosignatures that may become fossilized in the carbonate rock record. Structural biosignatures associated with microbial dolomite, which are microscopically observable, include characteristic shapes, such as dumbbell, spheroid or cruciform structures, and pervasive exopolymeric substance (EPS) matrices within which the mineral nucleates. The occurrence of these biostructures fossilized in geologic dolomite samples provides unambiguous evidence for the past presence of microorganisms. Identification of comparable biostructures associated with other more ambiguous biominerals may be significant physical evidence for the activity of microorganisms in a variety of terrestrial and planetary environments. Furthermore, the study of microbial dolomite precipitation provides valuable information on relevant environmental conditions that can be extrapolated to interpret paleoenvironments. In particular, microbial dolomite forms under hypersaline conditions often associated with a range of anaerobic microbial processes, such as bacterial sulfate reduction and/or anaerobic methane oxidation. The interactions of these complex microbial communities lead to the incorporation of characteristic carbon-isotope signatures reflecting the various metabolisms involved in the biomineralization. Additionally, the specific organic functional groups of metabolically produced organic molecules, which are included in modern and ancient biominerals, can be quantitatively compared using Electron Energy Loss Spectroscopy (EELS). Finally, combining these recently calibrated microbial biosignatures with the ultimate classic macroscopic evidence for microbial life, i.e. stromatolites, provides a powerful approach to corroborate the biogenicity of this earliest life form.
Bontognali T. R.
McKenzie Judith A.
Vasconcelos Crisógono
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