Discussion
The innermost layer of the Earth is the
Answer: D
Correct answer: Inner core
The inner core is a ball of iron and nickel about 1,220 km in radius at the centre of the Earth. Although its temperature approaches that of the surface of the Sun, it is solid, because the pressure there is so immense that it holds the metal in a solid state. That it is solid was deduced, not observed: Inge Lehmann showed in 1936 that S waves, which cannot travel through liquid, are absent beyond a certain distance while a reflected P wave reappears - evidence of a solid body inside a liquid shell. Outside it lies the liquid outer core, whose churning convection generates the Earth’s magnetic field. Beyond that is the mantle, much the largest layer by volume, and outermost the thin crust. Nobody has sampled any of this directly; the deepest borehole ever drilled reached about 12 km, not even through the crust.
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