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Methane: Fuel or Exhaust at the Emergence of Life?

Russell, Michael J. and Nitschke, Wolfang (2017) Methane: Fuel or Exhaust at the Emergence of Life? Astrobiology, 17 (10). pp. 1053-1066. ISSN 1557-8070. doi:10.1089/ast.2016.1599.

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As many of the methanogens first encountered at hydrothermal vents were thermophilic to hyperthermophilic and comprised one of the lower roots of the evolutionary tree, it has been assumed that methanogenesis was one of the earliest, if not the earliest, pathway to life. It being well known that hydrothermal springs associated with serpentinization also bore abiotic methane, it had been further assumed that emergent biochemistry merely adopted and quickened this supposed serpentinization reaction. Yet, recent hydrothermal experiments simulating serpentinization have failed to generate methane so far, thus casting doubt on this assumption. The idea that the inverse view is worthy of debate, that is, that methanotrophy was the earlier, is stymied by the “fact” that methanotrophy itself has been termed “reverse methanogenesis,” so allotting the methanogens the founding pedigree. Thus, attempting to suggest instead that methanogenesis might be termed reverse methanotrophy would require “unlearning”—a challenge to the subconscious! Here we re-examine the “impossibility” of methanotrophy predating methanogenesis as in what we have termed, the “denitrifying methanotrophic acetogenic pathway”. Advantages offered by such thinking is that methane would not only be a fuel but also a ready source of reduced carbon to combine with formate or carbon monoxide—available in hydrothermal fluids—to generate acetate, a target molecule of the first autotrophs. And the nitrate/nitrite required for the putative oxidation of methane with activated NO would also be a ready source of fixed nitrogen for amination reactions. Theoretical conditions for such a putative pathway would be met in a hydrothermal green rust-bearing exhalative pile and associated chimneys subject to proton and electron counter gradients. This hypothesis could be put to test in a high-pressure hydrothermal reaction chamber in which a cool carbonate/nitrate/nitrite-bearing early acidulous ocean simulant is juxtaposed across a precipitate membrane to an alkaline solution of hydrogen and methane.

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Additional Information:© 2017 Michael J. Russell and Wolfgang Nitschke, Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative Commons License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Submitted 30 September 2016. Accepted 20 March 2017. Online Ahead of Print: September 26, 2017. We dedicate this contribution to Isik Kanik for his untiring and enthusiastic backing of our work in this area. We also thank Elbert Branscomb, Grayson Chadwick, Laurie Barge, Stuart Bartlett, Christophe Sotin, Steve Vance, and the members of the Keck Institute for Space Studies workshop, Methane on Mars, organized by Yuk Yung, Pin Chen, and Ken Nealson, for discussions. M.J.R.'s research was supported by the National Aeronautics and Space Administration, through the NASA Astrobiology Institute under cooperative agreement issued through the Science Mission directorate; No. NNH13ZDA017C (Icy Worlds) at the Jet Propulsion Laboratory. No competing financial interests exist.
Group:Keck Institute for Space Studies
Funding AgencyGrant Number
Subject Keywords:Green rust; Methanotrophy; Nitrate reduction; Emergence of life
Issue or Number:10
Record Number:CaltechAUTHORS:20171017-042427729
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Official Citation:Russell Michael J. and Nitschke Wolfgang. Astrobiology. October 2017, 17(10): 1053-1066.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82400
Deposited By: Iryna Chatila
Deposited On:17 Oct 2017 21:30
Last Modified:15 Nov 2021 19:50

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