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Is the iron in the inner core of Earth trapped forever? Are there any mechanisms that allow some iron to leave the core and come to the surface (eg: magma convention)?

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No, we occasionally get fragments of upper mantle overthrust onto the Earth's crust, but then the specific gravity (density) contrast is not so great, roughly 2.7 to 3.0 for crust, about 3.2 for mantle. But the core is another matter. The density contrast is huge - the liquid outer core is between 9.9 and 12.2, whilst the solid core is estimated to be 12.6 to 13.0! (High pressure iron-nickel with some denser metals mixed in). Not only that, but the mantle is quite close to the surface, only tens of kilometres deep, whereas the Earth's core is 3000 kilometres below the surface. Sadly, there is no volcanic process that comes from even remotely that depth.

Alas - many geologists, myself included, would dearly love to sample the core and compare the composition to iron meteorites (assumed similar). There are many other questions of geochemistry and isotopic composition which might be answered if only we could sample that deep. Unfortunately it is way beyond even the most optimistic advances in technology, so we just have to theorize.

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  • $\begingroup$ The question would also allow for the possibility of the solid solution of core iron into mantle material across the core-mantle boundary. If this is happening, it must be at a very, very low level - and would be difficult if not impossible to trace.. $\endgroup$ – winwaed Aug 17 '16 at 13:12
  • $\begingroup$ Regarding winwaed's comment, wherever there is gravity there will be differential density-driven separation of siderophile and lithophile phases. That's maybe not so important at the mantle-core boundary, where the gravity is weak, but 1000 km (for example) above the mantle-core boundary, gravity and temperature will be a strong enough combination for pretty effective differentiation - the iron phase would have migrated to the core long ago, and especially during the hotter initial phase of planetary formation. That still leaves at least 2000 km to drill before reaching any iron. $\endgroup$ – Gordon Stanger Aug 17 '16 at 23:57

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