re: #66 KGxvi

something would have shown up in the archeological record by now.

I’ve always thought so, too, but one thing I learned from this video I hadn’t considered before: geologists estimate the entire surface crust of the Earth is replaced every 500 million years due to subduction and tectonic/seismic activity. No matter what structures or technology this hypothetical civilization might have possessed, there could very well be no easily detectable traces of their existence left in the physical record.