If planetesimal impacts were a source of early heat they indirectly connect with which process?

Correct answer: Density based differentiation

Direct answer: Option A, density-based differentiation. Planetesimals were small rocky bodies that struck the young Earth. Their repeated impacts converted motion energy into heat. Together with radioactive heat and compression, this heat helped make parts of the early Earth molten or soft. In a molten or partly molten body, heavy materials such as iron and nickel sank toward the centre, while lighter rocky materials moved upward. This separation according to density is called differentiation and produced broad internal layers such as the core, mantle and crust. Option A is therefore correct. Option B, photosynthesis, is a biological process that developed after life appeared and is not the result of impacts. Option C, ozone depletion, concerns atmospheric ozone and is unrelated to the direct internal sorting of Earth. Option D, modern weathering, is surface breakdown by water, air and organisms and is not the early heating process. Memory cue: impacts heat; heat permits melting; melting permits density separation.