Iron isotope biosignatures.
The (56)Fe/(54)Fe of Fe-bearing phases precipitated in sedimentary environments varies by 2.5 per mil (delta(56)Fe values of +0.9 to -1. 6 per mil). In contrast, the (56)Fe/(54)Fe of Fe-bearing phases in igneous rocks from Earth and the moon does not vary measurably (delta(56)Fe = 0.0 +/- 0.3 per mil). Experiments with dissimilatory Fe-reducing bacteria of the genus Shewanella algae grown on a ferrihydrite substrate indicate that the delta(56)Fe of ferrous Fe in solution is isotopically lighter than the ferrihydrite substrate by 1.3 per mil. Therefore, the range in delta(56)Fe values of sedimentary rocks may reflect biogenic fractionation, and the isotopic composition of Fe may be used to trace the distribution of microorganisms in modern and ancient Earth.
Beard
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BL
Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA. Laboratory, MS 183-301, 4800 Oak Grove Road, Pasadena, CA 91109-8009, USA. beardb@geology.wisc.edu
Johnson
C M
CM
Cox
L
L
Sun
H
H
Nealson
K H
KH
Aguilar
C
C
D018534:Earth, Planet; D006092:Gram-Negative Facultatively Anaerobic Rods / Q000378:metabolism; D007501:Iron / Q000032:analysis*; D007503:Iron Isotopes / Q000032:analysis*; D013058:Mass Spectrometry / Q000379:methods; D016081:Moon
D007503:Iron Isotopes; D007501:Iron