Is the process in planetary formation when heavy materials sink toward the planet's center and lighter materials accumulate near its surface.

a. orogenyb. superpositionc. ratificationd. differentiation

The correct answer is letter D. Differentiation is a process where different layers of a planetary body are separated into layers. This occurs in the development of protoplanets. With heavy materials sinking toward the planet's center, it creates a dense core with lighter elements toward the surface. This supports why iron is concentrated in the core. 

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