Plausibility/mechanisms for biogenic silica on a terrestrial planet with a reducing atmosphere

Situation:

• a large terrestrial planet (a 'super earth', around 9 earth masses with a surface gravity roughly double earth's) with a mostly hydrogen atmosphere and ammonia oceans (pressure is high enough that ammonia is liquid up to around 50°C)
• life uses ammonia as a solvent
• plants convert methane to biomass and release hydrogen (and animals obviously inhale hydrogen and exhale methane)

Question: Is it plausible for (the carbon based) life to use biogenic silica (= hydrated silica, SiO$_2$.$n$H$_2$O) as a structural material?

Ignore strength issues please (According to this research paper, silica is significantly stronger and less dense than bone, so that should not be an issue) - I'm interested in the chemistry of the situation.

As a terrestrial planet, water and CO$_2$ will be released by volcanic outgassing, and they have to go somewhere. Is it plausible that SiO$_2$ dissolves in the ammonia rivers/seas to be taken up by plants and animals, which then form hydrated silica?

I'm unsure about how oxides would behave/exist in a reducing atmosphere.

EDIT: (More details to make the question more specific)

On earth, silica forms (as quartz) from magma in volcanic rocks. That should be similar on this planet too. On earth it dissolves in water by hydration to form silicic acid, which is absorbed by the diatoms and other creatures which use silica as a structural material. On this planet, the seas are ammonia, not water.

That seems to leave two questions:

• Can silica dissolve in ammonia?
  The abstract of this paper says that it forms a SiO$_2$-NH$_3$ complex when exposed to gaseous ammonia and then dissociates to the molecule H$_2$NSiOOH under the influence of (UV to visible) light.
  Would this (or something else) work on the planet in question as a source of silica in the ammonia seas?
  Edit: (thanks to Kingledion) the full paper says that both reactions are exothermic, and that the formation of the initial complex has negligible activation energy. (Edit edit: I intended that edit to be a "yes, it would work" answer to the question)
• Can the organisms hydrate the silica internally?
  We produce ammonia and (a massive number) of other things as biochemical reaction intermediates and products - is it implausible that organisms on this planet can do the the same with water to produce biogenic hydrated silica?

posted about 7 years ago

Tharaib‭

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