It is well accepted that the outer core is made out of liquid iron and nickel, and as everything else it should tend to reach chemical equilibrium with its surrounding.

In particular, I would expect it to interact with the lower mantle through mixing and chemical reactions with the oxygen, silicates and other compounds. These interaction would result in the outer core slowly dissolving away into the mantle.

I would also expect this to happen in spite of the density gradient, that anyway should be less relevant down there, where the acceleration of gravity is much smaller than in the surface.

Why this dissolution doesn't happen? Why is the outer core stable?

As a bonus question inspired by this one: would any other blob of molten iron be stable anywhere in the mantle?

  • $\begingroup$ You are effectively lifting iron and lowering less dense materials hundreds of km. I think the gravitational potential energy is greater than the energy of solution (or whatever the physical chemistry terminology). I unsuccessfully looked for a quantitative treatment while considering Why is the core of Earth in a reduced state? (Fe and Ni). $\endgroup$ – Keith McClary Apr 15 at 18:12
  • $\begingroup$ @KeithMcClary Segregation of materials by density is very intuitive but chemical mixing although less intuitive is surprisingly "powerful". Otherwise, all the heavy water (aka deuterium oxide) in the oceans would be at the bottom of deep trenches, and it is not the case. Look at this question that talk about the same in the atmosphere earthscience.stackexchange.com/q/13144/11908 $\endgroup$ – Camilo Rada Apr 15 at 18:50
  • $\begingroup$ In this discussion of Differentiation Mechanisms they seem to assume no solubility or chemical reactions. $\endgroup$ – Keith McClary Apr 15 at 19:24
  • $\begingroup$ KeithMcClary very interesting text, thank's for bringing it up. And indeed, after browsing trough a few sections they seem to assume that "Liquid metal separates rapidly from liquid silicate", like oil and water, and they don't mix later. Very interesting. I wonder what's @Gimelist opinion about this. $\endgroup$ – Camilo Rada Apr 15 at 21:38
  • $\begingroup$ Chemical equilibrium also includes gravity based segregation. $\endgroup$ – John Apr 17 at 13:29

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