The Silurian Hypothesis

A descent through deep time built on a real, peer-reviewed thought experiment by Gavin Schmidt and Adam Frank: if another industrial species had lived here long before us, what traces would survive in the rock?

It exists because the question is usually asked by fringe theorists and waved away by everyone else. Asked properly, it becomes a sharp lesson in how little survives — three centuries of our own industry would be about a centimetre of sediment.

What to take from it: an absence of evidence only means something once you know what the evidence would look like. Here it would be a faint chemical signal, not ruins.