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Life associated with a 2.76 Ga ephemeral pond?: evidence from Mount Roe #2 paleosol.
1California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena 91125, USA. rye@gps.caltech.edu
Geology
|September 7, 2001
Summary
Ancient microbes called methanotrophs inhabited ephemeral ponds 2.765 billion years ago, as evidenced by their unique carbon isotopes in Western Australia. This discovery pushes back the geologic record of land-based methanotrophy by 1.5 billion years.
Area of Science:
- Geoscience
- Paleontology
- Biogeochemistry
Background:
- The Mount Roe #2 paleosol in Western Australia preserves ancient environmental conditions.
- Organic carbon with negative delta 13C values suggests microbial activity.
Purpose of the Study:
- To investigate the origin of dark sericitic material in the Mount Roe #2 paleosol.
- To determine the implications of microbial life for Late Archean atmospheric conditions.
Main Methods:
- Analysis of organic carbon content and delta 13C isotopic values.
- Microscopic and chemical analysis of paleosol material textures and composition.
Main Results:
- Dark sericitic material contains 0.05-0.10 wt% organic carbon with delta 13C values from -33% to -51% PDB.
- Isotopic and textural evidence indicates the presence of methanotrophs in ephemeral ponds.
- This finding potentially extends the geologic record of terrestrial methanotrophs by 1.5 billion years.
Conclusions:
- Methanotrophs inhabited ephemeral ponds and were transported by water.
- Late Archean atmospheric methane levels may have been high (> or = 20 (mu)atm).
- Elevated methane could have provided radiative forcing to counteract the faint young sun and prevent glaciation.
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