Why does our planet have an iron core, rather than one made of another abundant element such as silicon?
Alex McDowell
London, UK
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Iron is more dense and hence, when the young Earth was molten, it tended to sink. Lighter elements, such as silicon and aluminium, floated to the surface and, as Earth cooled, the crust contained mainly the lighter elements.
Ken Appleby
Ledbury, Herefordshire, UK
Iron is the densest abundant element and gravitationally settles at the core, displacing all less dense materials. It is the densest abundant element because it is the final product of stellar nuclear fusion.
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