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.