I've always thought that the process of planetary accretion was energetic enought to keep the proto-Earth entirely molten, and that the subsequent evolution of the planet (the formation of the crust, etc...) was simply cenetered 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 the "Iron Catastrophe", that ocurred 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 Iron Catastrophe the Earth had a primitive solid surface? That this surface was turned into a magma ocean because of the feedback loop of the Iron Catastrophe 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 enought 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 enought energy to melt the entire object they would have made possible Earth's differentiation way before the Iron Catastrophe)? Does these impacts were unfrequent enought that the embryo could have solidified and cooled down before the next accreating event? How can accretion form an undifferentiated Earth before the Iron Catastrophe at all?
  • If a planet is accreted only from non-radioactive material then we should expect an Earth-size planet with no differentiated interior? Since radiactive 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 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 at 11:49
  • $\begingroup$ 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 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 at 11:58
  • $\begingroup$ 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 at 11:59

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