Just thinking off the cuff and channeling a bit of Isaac Arthur here. Coming from the angle of a non-native intelligence colonizing Earth in the super distant

Just thinking off the cuff and channeling a bit of Isaac Arthur here. Coming from the angle of a non-native intelligence colonizing Earth in the super distant past, there may not be many or any terrestrial remains over such a long span of time. It’s reasonable to think “aliens” would not burn coal and oil for energy. If they crossed the gulf of space, they likely used fusion or some other power source. A ground side civilization could sift helium3 from the oceans for thousands of years without a noticeable depreciation. If they used power satellites, those would likely have fallen from orbit or been knocked out of the Earth-Moon system within hundreds to thousands of years. Within human history, many of the same geographical areas of the world have been good places to live for thousands of years. But when you extend that to hundreds of thousands to millions of years, those places generally change drastically and disappear. One could assume, for the sake of argument, that aliens colonizing Earth might have similar biological needs as we do and would live in similar areas of the distant past. We might not easily find those places now given environmental changes over geological ages. We also are still very early in exploring the solar system. It’s plausible there could be remnants of mining and manufacturing in places we haven’t looked. It’s important to remember that if your civilization is colonizing a new system, you’re already a space based society. It’s then reasonable to expect little on the ground industrialization since most of your infrastructure will be in space. There’s a new study talking about solar electrostatic effects on the Moon and how it causes lunar dust to rise and drift around despite no atmosphere. Given long enough spans of time this might even conceal evidence of prior space-based industrialization. One big red flag to me that this hasn’t happened in Earth’s history is the biological record. We have a fairly good overall map of biology over large areas of the world. Everything alive here seems to come from here. There’s nothing alive that doesn’t appear to use the same general base chemistry and biology as everything else. If some aliens showed up a hundred million years ago, we might expect to see some distantly evolved branches of life that are somewhat different in at least DNA or other chemistry. We might find something like this but it’s unlikely. The follow-on to that might be an argument that all current life is descended from some ancient aliens. That could be true but it would be nearly impossible to tell at this point. All life seems to have a common descent with no aberration, so following up on this line of thought is extremely difficult to test for. We would need to find examples of life outside of Earth before we could make comparisons to investigate that hypothesis.