Difference in composition of Earth's core and crust is strong evidence of which process?

Correct answer: Density based differentiation

The direct answer is B: density-based differentiation. In the early Earth, heating caused materials to separate according to density. Dense materials, especially iron and nickel, moved downward toward the centre and formed much of the core. Less-dense silicate materials remained nearer the outside and contributed to the mantle and crust. The reasoning is: different densities caused movement and separation; separation produced layers with different compositions; the core–crust difference is evidence of differentiation. Option A, photosynthesis, is a biological process in green plants and cannot explain Earth’s internal layers. Option B is correct because it describes gravitational separation by density. Option C, solar wind, is a stream of charged particles from the Sun and does not create the core’s heavy-metal concentration. Option D, condensation, means gas changing to liquid and may describe an early cooling step, but it does not specifically explain the separation of heavy core material from lighter crustal material. Memory cue: heavy sinks, light stays outward—this is differentiation.