I've always thought that the process of planetary accretion was energetic enough to keep the proto-Earth entirely molten, and the subsequent evolution of the planet (the formation of the crust, etc...) was simply centered on its cooling by gradual liberation of the trapped heat (from those planetesimal collisions and radioactive decay).

But recently I've read that there was a particular event called core-mantle differentiation, or the "Iron Catastrophe", that occurred after the formation of Earth (and before he formation of the Moon), which transformed "an undifferentiated mass of solid rock" into a magma ocean.

  • Does this means that previous to the core-mantle differentiation, the Earth had a primitive solid surface? That this surface was turned into a magma ocean because of the feedback loop of core-mantle differentiation and then, when things cooled down, a second generation crust formed (which was later destroyed by Theia's giant impact)?
  • Does the process of rapid accretion of planetary embryos trapped so little heat inside Earth that the additional heat from radioactive decay was needed to build up enough temperature to melt the iron afterwards? Does this mean that each of the planetesimal impacts melted only part of the embryo (I guess that if they could yield enough energy to melt the entire object they would have made possible Earth's differentiation way before the core-mantle differentiation)? Does these impacts were infrequent enough that the embryo could have solidified and cooled down before the next accreting event? How can accretion form an undifferentiated Earth before the core-mantle differentiation at all?
  • If a planet is accreted only from non-radioactive material, should we expect an Earth-size planet with no differentiated interior? Since radioactive decay was apparently needed for the "Iron Catastrophe".
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    $\begingroup$ Excellent questions, and there are no clear answers. Just last week we had our department seminar exactly about this topic with some of the greatest minds thinking about this together. We simply do not know. Embryos could have been already differentiated before impacting the proto-Earth, or they could have not. It could been very rapid, or more protracted. Was chemical equilibrium achieved on a planetary scale, or not? Each of these factors and more would change any answer given to your question. $\endgroup$
    – Gimelist
    Jun 1, 2020 at 11:05
  • $\begingroup$ @Gimelist Wow that's fascinating. Are there any papers I could get into to understand a bit more of this debate? I'm a physicist and just starting to learn about geology and planetary formation so I feel that I need someone to guide me. I would also need good resources for the Iron Catastrophe since there's a lack when you search this term, is it not the main hypothesis about planetary differentiation? Why? All of that would at least make me more confortable with what it is knwon and what not. $\endgroup$
    – Swike
    Jun 1, 2020 at 11:49
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    $\begingroup$ Yes, there are many papers. We geochemists don't really call it "iron catastrophe". What you're looking for is the "core mantle differentiation". $\endgroup$
    – Gimelist
    Jun 1, 2020 at 11:52
  • $\begingroup$ @Gimelist Oh nice. I was suspecting that this was not a popular term. Is it the same concept or is the Iron Catastrophe a particular hypothesis for Core-Mantle differentiation. Sorry for so many questions. $\endgroup$
    – Swike
    Jun 1, 2020 at 11:58
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    $\begingroup$ The core mantle differentiation is the event where you took most of the metallic iron, dumped it into the core, and left the silicate residue as the mantle. If this is what the iron catastrophe is for you, then yes. $\endgroup$
    – Gimelist
    Jun 1, 2020 at 11:59


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