Why is Earth's nucleus mostly made from iron?
1) Iron is the most common siderophile
2) Earth does not contain enough oxygen to bind to all iron. While a lot of iron is bound to oxygen and found in rocks, some of it concentrated in iron ores and some scattered, much iron is left over as metal.
3) Iron with siderophile alloying elements is denser than rocks and sinks to centre. Everything else is either siderophile and mixed with iron, or lithophile which mixes with less dense rocks and floats in top of iron.
We have a second generation solar system, which means that much of the material came from the death of a previously-existing star. As stars gradually reach the end of their life, their chemical composition changes in the direction of the element that has the lowest amount of nuclear potential energy, which is iron. Iron is to nuclear reactions what ash is to combustion, an end product out of which no more energy can be extracted.
The catastrophe looks like Archimedes' law. Thanks for every answers. It is nice to understand nature as much as it is possible.
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