4 ms·

That's the oldest surface land, but the oldest crust is 4.4 billion years in Australia, and there are other places with less-old-but-still-billions crust. Natur

• yellowapple 7y ago
  Surface land (current or former) is the only really relevant source of potential evidence here, though (unless we're specifically looking for subterranean civilizations, or perhaps for remains of old mines or wells).
  • caymanjim 7y ago
    Surface land is a bit of a misnomer here. While the crust is 4.4B years old in Australia, that doesn't mean all 4.4B years are sub-surface. The top surface there is new, but there are exposed areas going back billions of years. This is how all fossils are found; the oldest surface is the 1.8M Negev desert, but we constantly find 300M year old dinosaurs sticking out of the sides of river valleys and other eroded areas. My point is that we'd also find evidence of a billion-year-old advanced civilization the same way, and that in Australia in particular, you can go all the way back to the formation of the planet.