1. Research Center for the Evolving Earth and Planet, Tokyo Institute of Technology,
2. Department of Earth and Planetary Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
3. Department of Environmental Science and Technology and
4. Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
5. SORST project, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012, Japan
6. Department of Earth Science and Astronomy, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan

Correspondence to: Yuichiro Ueno^1,3,5 Correspondence and requests for materials should be addressed to Y.U. (Email: yueno@depe.titech.ac.jp).

Abstract

Methanogenic microbes may be one of the most primitive organisms¹, although it is uncertain when methanogens first appeared on Earth. During the Archaean era (before 2.5 Gyr ago), methanogens may have been important in regulating climate, because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity² during these times. Nevertheless, no direct geological evidence has hitherto been available in support of the existence of methanogens in the Archaean period, although circumstantial evidence is available in the form of 2.8-Gyr-old carbon-isotope-depleted kerogen³. Here we report crushing extraction and carbon isotope analysis of methane-bearing fluid inclusions in 3.5-Gyr-old hydrothermal precipitates from Pilbara craton, Australia. Our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than -56 included within original precipitates. This provides the oldest evidence of methanogen (> 3.46 Gyr ago), pre-dating previous geochemical evidence by about 700 million years.

1. Research Center for the Evolving Earth and Planet, Tokyo Institute of Technology,
2. Department of Earth and Planetary Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
3. Department of Environmental Science and Technology and
4. Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
5. SORST project, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0012, Japan
6. Department of Earth Science and Astronomy, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan

Correspondence to: Yuichiro Ueno^1,3,5 Correspondence and requests for materials should be addressed to Y.U. (Email: yueno@depe.titech.ac.jp).

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