Tough to do - but you just blew my mind!

“Wait a second,” he said. “How do you know we’re the only time there’s been a civilization on our own planet?”

It took me a few seconds to pick my jaw off the floor. I had certainly come into Gavin’s office prepared for eye rolls at the mention of “exo-civilizations.” But the civilizations he was asking about would have existed many millions of years ago. Sitting there, seeing Earth’s vast evolutionary past telescope before my mind’s eye, I felt a kind of temporal vertigo. “Yeah,” I stammered, “Could we tell if there’d been an industrial civilization that deep in time?”

...[T]he oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old — older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. Go back much farther than the Quaternary and everything has been turned over and crushed to dust.

And, if we’re going back this far, we’re not talking about human civilizations anymore. Homo sapiens didn’t make their appearance on the planet until just 300,000 years or so ago. That means the question shifts to other species, which is why Gavin called the idea the Silurian hypothesis, after an old Dr. Who episode with intelligent reptiles.

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