n the grand sweep of Earth’s four-billion-year history, 300 years is barely a blink. And yet, that blink — our industrial era — has already reshaped the atmosphere, oceans, and sediments. If civilization collapsed tomorrow, would anything of us remain 100 million years from now? Could some alien beings visiting Earth in the future ever tell that this planet was inhabited by an advanced civilization? More startling still: if another civilization once existed on Earth long before us, could we even tell?
This question lies at the heart of the Silurian Hypothesis — a playful yet serious scientific proposition by NASA climate scientist Gavin Schmidt and astrophysicist Adam Frank, detailed in a 2018 paper in the International Journal of Astrobiology. The name nods to the Silurians, a fictional species of ancient intelligent reptiles from Doctor Who, but the premise is grounded in geology, astrobiology, and climate science.
“We are not however suggesting that intelligent reptiles actually existed in the Silurian age,” the authors clarify in their paper, just to be sure no one misreads them. “Nor that experimental nuclear physics is liable to wake them from hibernation.”
At its core, the Silurian Hypothesis asks: if an industrial civilization arose millions of years ago — say, during the Devonian or the Paleocene — would we find any trace of it today?
According to Schmidt and Frank, the odds are slim.
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