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Related Experiment Videos

Iron isotope biosignatures.

B L Beard1, C M Johnson, L Cox

  • 1Department 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

Science (New York, N.Y.)
|September 18, 1999
PubMed
Summary
This summary is machine-generated.

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Iron isotope variations in sedimentary rocks suggest microbial influence. This study shows biogenic fractionation by iron-reducing bacteria, offering a new way to track ancient microorganisms using iron

Area of Science:

  • Geochemistry
  • Microbiology
  • Isotope Geochemistry

Background:

  • Iron isotope ratios ((56)Fe/(54)Fe), measured as delta(56)Fe, show significant variation in sedimentary rocks (+0.9 to -1.6 per mil).
  • In contrast, iron-bearing phases in igneous rocks from Earth and the Moon exhibit minimal isotopic variation (delta(56)Fe = 0.0 +/- 0.3 per mil).
  • This discrepancy suggests a distinct fractionation process in sedimentary environments.

Purpose of the Study:

  • To investigate the role of microbial activity in causing iron isotope fractionation in sedimentary environments.
  • To determine if iron isotope signatures can serve as a tracer for microbial distribution in geological records.

Main Methods:

  • Experimental incubation of dissimilatory iron-reducing bacteria (Shewanella algae) with a ferrihydrite substrate.
Keywords:
NASA Center JPLNASA Discipline Exobiology

Related Experiment Videos

  • Measurement of iron isotope ratios ((56)Fe/(54)Fe) in both the bacterial substrate and the resulting dissolved ferrous iron.
  • Comparison of experimental fractionation with natural variations observed in sedimentary and igneous rocks.

    • Main Results:

    • Experiments demonstrated that Shewanella algae caused a significant isotopic fractionation, with dissolved ferrous iron being lighter than the ferrihydrite substrate by 1.3 per mil (delta(56)Fe).
    • This experimentally derived biogenic fractionation value aligns with the range of delta(56)Fe values observed in natural sedimentary rocks.
    • The lack of significant fractionation in igneous rocks supports a biological origin for sedimentary iron isotope variability.

    Conclusions:

    • The wide range of iron isotope values in sedimentary rocks is likely a result of biogenic fractionation by iron-reducing microorganisms.
    • Iron isotope composition serves as a potential biomarker for tracing the presence and activity of microorganisms in both modern and ancient Earth environments.
    • This research opens new avenues for using stable iron isotopes to reconstruct paleoenvironmental conditions and microbial evolution.