The early differentiation of Earth into a mantle and a core was created by ________.
A. nuclear fission in the center of Earth, which converted hydrogen and helium to iron
B. the magnetic attraction between cations and anions of iron and nickel
C. gravitational accretion of iron-rich particles in the core, followed by silicate-rich particles in the mantle
D. the buildup of heat and the melting of iron, which was pulled by gravity to the center of Earth
Answer: D
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