The fascinating New York Times article Gas That Makes a Mountain Breathe Fire Is Turning Up Around the World talks about the Flames of Chimaera and the Deep Carbon Observatory:

And a series of studies published by a group of international scientists known as the Deep Carbon Observatory is showing that this source of gas is more common on our planet than previously known.

“We have discovered these unusual types of methane in many, many sites. It’s not a rare phenomenon,” said Giuseppe Etiope, a member of the group who helped discover the cause of the flames of Chimaera in 2014. (emphasis added)

This question is about the possible sources of hydrogen that resulted in what the NYTimes calls "unusual types of methane":

For years, Deep Carbon Observatory researchers have collected and analyzed gas samples from hundreds of diverse sites. And using special tools to figure out where the methane came from, they’ve discovered Earth’s basic recipe: Take hydrogen from water. Mix with inorganic carbon from minerals or gas. Add another metal-rich mineral to get the process going, and voilà — abiotic methane.

The hydrogen often comes from serpentinization, when water percolates usually through rocks from the mantle. But the recipe varies. Different sites may use different minerals or carbons sourced from their environments: Hydrogen may come from friction, or radiolysis, instead of serpentinization. Temperatures may range from below 250 degrees Fahrenheit, which can still support life, to some 900 degrees Fahrenheit, which can’t. (emphasis added)

Serpentinization is nicely explained in @Gimelist's excellent answer to the question What is serpentinization, in the context of disappearance of surface water on Mars?

Question: How can the hydrogen in this abiotic methane come from

  1. Friction
  2. Radiolysis

Possibly helpful (Open Access):

  • 1
    $\begingroup$ My answer is more focused in how bacteria make profite of friction and radiolysis to generate biotic methane but there is also a non biological formation of CH4. $\endgroup$ – user12525 May 7 '19 at 12:06
  • 1
    $\begingroup$ Thanks uhoh. I guess as the hydrogen comes from water it should have an isotopical signal with heavy H. Conversely, life prefers ligth H. But that's talking only about the abiotic origin of the H, and not methane, that can be formed by inorganic proccess. I may complete my answer talking about that a bit, after investigating a bit. The isotopes I would search for to distinguish between abiotic and biotic methane would be C13/C12. $\endgroup$ – user12525 Jun 25 '19 at 9:44

I found this paper 1 trying to understand what is radiolysis. The decomposition of water by ionization happens at basaltic aquifers on the seafloor, close to seabed.

"Water radiolysis is the decomposition of water molecules by ionizing radiation produced during the decay of radioactive elements (Debierne, 1914; Le Caër, 2011). The principal radioactive elements that produce ionizing radiation in basalt are uranium (238U and 235U), thorium (232Th), and potassium (40K), which collectively emit alpha (α), beta (β), and gamma (γ) radiation as they and their daughter nuclides decay. Transfer of energy from this radiation excites and ionizes water molecules, producing several chemical species: eaq-, HO•, H•, HO2•, H3O+, OH-, H2O2, and H2 (Spinks and Woods, 1990; Le Caër, 2011)."

"The oceanic basement contains the largest aquifer on Earth. Its fractured rock contains nearly 2% of Earth’s total volume of seawater (Johnson and Pruis, 2003). Although the extent of life and microbial activity in oceanic basement is not well known, a variety of evidence suggests that microbes reside within the aquifer (Cowen et al., 2003; Edwards et al., 2012; Jungbluth et al., 2013; Lever et al., 2013; Orcutt et al., 2013). Fisk et al. (1998) and Staudigel et al. (2008) report weathering textures suggestive of microbial alteration in subseafloor basaltic glass."

For subseafloor environments, we are particularly interested in the production of the reductant H2. Many organisms catabolically utilize H2, including methanogens, sulfate-reducers, iron reducers, and nitrate reducers (Fang and Zhang, 2011). There is evidence that some of these organisms, specifically sulfate reducers and methanogens, are active in subseafloor basalt (Lever et al., 2013). Radiolysis undoubtedly occurs in subseafloor basalt, as both water and radiation are present. Edwards et al. (2012) suggested that in the old and relatively weathered basaltic basement of the South Pacific Gyre (SPG), radiolytic H2 may be the dominant electron donor.

Trying to understand how hydrogen can be formed by friction I found this other one 2 where the author asociates it to earthquakes, listing three possible origins for hydrogen and saying the frictional origin is still a not well known process. Apparently it happens at fault systems when there are mouvements on lithosphere:

In the last few decades, three different abiotic H2 generation processes have been proposed:

  • (1) water–rock redox reactions, mostly under hydrothermal conditions [Janecky and Seyfried, 1986; Coveney et al., 1987],
  • (2) radiolytic reactions of H2O [Savary and Pagel, 1997], and
  • (3) mechanoradical formation on wet fault surfaces during earthquakes [Wakita et al., 1980].

H2 production by peridotite‐ water and komatiite‐water hydrothermal reactions, as modern and ancient analogs, respectively, has been quantitatively estimated in laboratory experiments [Seyfried et al., 2007; Yoshizaki et al., 2009]. Radiogenic production of H2 is supported by the analysis of H2‐bearing fluid inclusions in quartz containing U‐bearing minerals [Dubessy et al., 1988], and has been quantitatively estimated in a laboratory g‐irradiation experiment [Lin et al., 2005]. The H2 flux per unit of surface area from redox reactions has been estimated to be 3 × 10−4 mol/m2 yr from a 1 km column of mafic/ultramafic rock with 10 wt% FeO [Sleep and Zoback, 2007], and the estimated flux from water radiolysis in the Witwatersrand basin, South Africa, is 8 × 10−6 mol/m2 yr [Lin et al., 2005]. In contrast, the H2 flux associated with earthquakes and its significance in subsurface ecosystems has not yet been explored in either the field or laboratory.

After making experimental flux calcs the paper says this mechanism may have been important for methanogens. And not only eartquakes but meteorite impacts too may have been a source of mollecular hydrogen for primigenious life not only on Earth but on other planets.

"Thus, seismic activity and the consequent release of H2 might have sustained subsurface microbial communities as long ago as 3.8 Ga. Moreover, mechanoradical H2 generation can be induced by meteorite impacts as well as by earthquakes, and thus might play an important role in the evolution of subsurface biosphere not only on Earth but also on other planets."

1 Dzaugis Mary E., Spivack Arthur J., Dunlea Ann G., Murray Richard W., D’Hondt Steven (2016). "Radiolytic Hydrogen Production in the Subseafloor Basaltic Aquifer" Frontiers in Microbiology, 7, ISSN=1664-302X

2 T Hirose, S Kawagucci, K Suzuki (2011) "Mechanoradical H2 generation during simulated faulting: Implications for an earthquake‐driven subsurface biosphere." Geophysical research letters.

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  • $\begingroup$ It seems that Universal_learner has been quite busy learning! $\endgroup$ – uhoh May 7 '19 at 11:15
  • $\begingroup$ It is always a pleasure to learn new things @uhoh :) $\endgroup$ – user12525 May 7 '19 at 11:16

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