Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.b24a..01v&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #B24A-01
Mathematics
Logic
0406 Astrobiology And Extraterrestrial Materials, 0419 Biomineralization, 0424 Biosignatures And Proxies, 1505 Biogenic Magnetic Minerals, 1527 Paleomagnetism Applied To Geologic Processes
Scientific paper
The term magnetofossil was introduced by Joseph Kirschvink and co-workers in the mid-eighties to describe fossil remains of magnetosomes in marine sediments after the discovery of magnetotactic bacteria by Richard Blakemore in the mid-seventies. Magnetofossils were initially considered as stable carriers of natural remanent magnetization (NRM) in sedimentary rocks. In the protracted debate over the possible bacterial origin of magnetite in carbonate in Martian meteorite ALH84001, the term magnetofossil has also been used as evidence for biological activity (i.e., biosignature) in ancient terrestrial and extraterrestrial environments. Magnetic methods sensitive to the single domain (SD) size specificity have been developed to detect the magnetosomes, distinction between biogenic and non-biogenic magnetic phases based upon magnetic analysis is difficult. In addition, with the discovery of SD magnetite formed by thermophilic bacteria isolated from deep subsurface and biogenic magnetite produced through reduction of Fe(III) by a variety of dissimilatory Fe(III)-reducing bacteria (DIRB) in diverse environments and a wide range of temperatures, new criteria has to be established to enable the distinction between biogenic and non-biogenic magnetic phases. Laboratory experiments have shown that the size and shape of magnetic phases formed by these bacteria strongly depend upon the growth culture conditions. Slight variation in the chemical composition, temperature and/or redox condition of the growth medium resulted in deviation in crystal morphology of magnetite making the morphological distinction between biogenic (magnetofossils) and non-biogenic magnetic minerals difficult. Magnetic phases with unique shape, morphology and organization have been observed in a variety of bacteria cultures. The existence of these types of magnetofossils in the natural environment, however, has not been explored. Although alternative preparation and analytical techniques have been developed for the isolation and characterization of magnetofossils, geochemical, mineralogical and morphological criteria need to be established to enable the recognition of all types of biogenic and non-biogenic magnetic phases in sediment, soil and rock. Although combined molecular, microbiological and mineralogical investigation has been conducted to understand the processes of bacterial induced mineralization, the mechanisms of extracellular formation of magnetite are poorly understood.
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