In 2018 a NASA climate scientist and an astrophysicist quietly published a paper asking the question nobody had thought to ask: if an industrial civilization had already existed on Earth — tens or hundreds of millions of years before us — would anything remain today for us to find? Their answer is genuinely unsettling.
The original arXiv preprint. A NASA climate modeler and a University of Rochester astrophysicist ask what geological fingerprint an industrial civilization would leave — and how you would tell it apart from a purely natural event.
The clean overview — including why it's named after a race of ancient bipedal reptiles from a 1970 Doctor Who serial, and why neither author actually believes there was a prior civilization.
Matt O'Dowd walks through the math of detectability: after a few million years, a city becomes a thin, unreadable smear in a sedimentary layer. Concrete, glass, roads — all gone.
Adam Frank's own essay explaining why the honest answer is 'we can't yet rule it out' — and why that sentence should bother you more than it does.
A cleaner walkthrough of the argument for a non-specialist reader: fossilization is vanishingly rare, and 'civilizations' rarely last long enough on geological timescales to matter.
The co-author, in his own words on his climate-science blog. Notice how much of the paper is really about the Anthropocene — what we ourselves are leaving in the rocks right now.
A short, strange literary essay treating the hypothesis as a mirror: what we suspect about prior worlds is really what we fear about our own.
The flip of the question. If nothing of a prior civilization survives, then nothing of ours will either — the only exceptions may be a few oddities in the isotope record and some very confused future geologists.