Repeated impacts on early Earth increased which condition?

Correct answer: Extreme heat and melting

The direct answer is A: repeated impacts increased extreme heat and melting on early Earth. During planetary formation, planetesimals and other bodies struck the growing Earth at high speed. Their motion energy changed largely into heat on impact. The growing mass also produced pressure and additional internal heating, while radioactive materials contributed heat. As a result, much of the early surface and interior became molten or partially molten, making Earth hot and unstable. The reasoning is: many high-energy impacts → impact energy becomes heat → temperature rises → rocks melt and the surface remains partly molten. Option A is correct because it identifies the physical result of repeated collisions. Option B is wrong because dense greenery requires a later stable environment, liquid water, soil, and life; it could not exist during this intensely hot stage. Option C is wrong because repeated impacts worked against a permanent ice sheet by supplying heat. Option D is wrong because humans appeared vastly later and could not live on the early molten planet. “Extreme heat and melting” does not mean every part was always completely liquid; it means impacts strongly promoted heating and melting. Memory cue: early impacts were like repeated giant blows, converting motion into heat.