[throwaway5752]

... Do you know about the iron catastrophe (https://en.wikipedia.org/wiki/Iron_catastrophe), banded iron formations (https://en.wikipedia.org/wiki/Banded_iron_formation), and the oxygen catastrophe (https://en.wikipedia.org/wiki/Great_Oxygenation_Event) and how they are related? Would it really be possible for us to not notice prior large-scale industrial mining of iron? Your point about lunar exploration is great, but it's also very likely there has never been industrialized life like us in Earth's history.