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Related Experiment Video

Updated: Apr 3, 2026

Using Flexible Gold-Titanium Reaction Cells to Simulate Pressure-Dependent Microbial Activity in the Context of Subsurface Biomining
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Metalliferous Biosignatures for Deep Subsurface Microbial Activity.

John Parnell1, Connor Brolly2, Sam Spinks1,3

  • 1Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, UK.

Origins of Life and Evolution of the Biosphere : the Journal of the International Society for the Study of the Origin of Life
|September 18, 2015
PubMed
Summary

Deep subsurface microbial activity is indicated by reduction spheroids in red beds. These metalliferous structures, formed by iron-reducing bacteria, serve as potential biosignatures for exploring life on Earth and Mars.

Keywords:
Deep biosphereDeep subsurfaceIron-reducing bacteriaMetalliferous biosignatureRaman spectroscopyReduction spheroidSelenium

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Area of Science:

  • Geomicrobiology
  • Astrobiology
  • Geochemistry

Background:

  • Microbial-metal interactions are traditionally studied in shallow subsurface environments.
  • Recent findings suggest significant microbial activity occurs in the deep subsurface.
  • Reduction spheroids in terrestrial 'red beds' provide evidence for deep microbial processes.

Purpose of the Study:

  • To investigate the formation and implications of reduction spheroids as indicators of deep subsurface microbial life.
  • To assess the potential of these structures as biosignatures for extraterrestrial exploration, particularly on Mars.

Main Methods:

  • Analysis of reduction spheroids in fluvial, lacustrine, and aeolian red beds.
  • Identification of iron (Fe (III)) reducing bacteria as the primary agents of spheroid formation.
  • Utilizing Raman spectroscopy to analyze quartz grains within spheroids for biosignature evidence.

Main Results:

  • Reduction spheroids contain metalliferous cores and exhibit morphologies indicative of deep subsurface formation post-compaction.
  • Iron (Fe (III)) reducing bacteria facilitate the reduction of various metals (V, Cu, Mo, U, Se) within these spheroids.
  • Color contrasts within spheroids, detectable by Raman spectroscopy, serve as viable biosignatures.

Conclusions:

  • Microbial action is the most plausible explanation for the formation of reduction spheroids.
  • These metalliferous structures are significant biosignatures for deep subsurface microbial activity.
  • Reduction spheroids offer promising targets for detecting life in subsurface environments on Earth and Mars.