Did Silicates Form on Early Earth Without Basic Aqueous Solutions?

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Discussion Overview

The discussion revolves around the formation of silicates on early Earth, specifically questioning whether silicates could form without basic aqueous solutions during a period characterized by molten silicon and gas of silica. The scope includes theoretical and conceptual aspects of geochemistry and mineral formation.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions how silicates could form without basic aqueous solutions, suggesting that such conditions were not present during the early Earth period.
  • Another participant proposes that silicates can form through the reaction of metal oxides with silica, even without water, and notes that geological time allows for slow reactions to occur.
  • A further inquiry is made regarding the reaction mechanisms involved in silicate formation, particularly in the absence of polar molecules like water, and whether Gibbs free energy plays a role in facilitating these reactions.
  • One participant expresses uncertainty about the detailed mechanisms of silicate formation but notes that silicates are thermodynamically more stable than mixtures of silica and metal oxides.
  • A reference to a specific academic source is provided, suggesting it contains relevant information on the topic of high temperatures and pressures related to silicate formation.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms and conditions under which silicates can form, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are limitations regarding the detailed mechanisms of silicate formation, including assumptions about reaction conditions and the role of Gibbs free energy, which remain unclear.

Ferrus
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How did the silicates form during the period in which a gas of silica coalesced into a ball of molten silicon? I thought silicate typically only forms in basic aqueous solutions, which clearly did not exist at this period.
 
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One of the ways of synthesizing salts is - metal oxide plus acidic anhydride -> salt. In the presence of metal oxides silica will react creating silicates - slowly, but there was plenty of geological time. Plus, once the mixture got hot, reaction speed up.
 
Excellent thank you.

What is mechanism of their reaction? I have seen the mechanisms for oxides on water with both acidic and basic characters, electrostatics, etc... how without the polar molecules of water are they able to mediate a reaction? Is it just a matter of gibbs free energy reduction, along with a large activation energy (hence slow speed under normal conditions) reflecting the very awkward transition molecules?
 
No idea about the detailed mechanism, for sure silicates are thermodynamically much more stable than silica/metal oxides mixture. Oxides - especially of first two groups metals - are mostly ionic, which probably plays a role.
 
There is quite a lot of useful information in Navrotsky p300ff (The Physics and Chemistry of Earth Materials - Cambridge) in the chapter on high temperatures and high pressures and plenty of references at the end of that chapter.

Go well
 

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