The Earth’s core, as the word implies, is the innermost part of the Earth, almost 3,000 kilometers deep. This core consists of an inner part that is solid, with a liquid outer core around it. Both consist of metals, mainly iron. The outer core is liquid because the temperature is thousands of degrees high, but in the inner core the pressure is so high that the metal solidifies into a sphere. That sphere is about the size of Pluto and grows slowly (in this article you can read exactly how that core is put together).
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