The Silurian hypothesis is a thought experiment developed by two scientists in a 2018 paper. Basically it goes like this:
There's been enough fossil fuel on Earth since the end of the Carboniferous, 350 million years ago, to support an industrial civilization. If such a civilization existed on Earth, millions or tens of millions of years ago, what evidence of it might still exist after all this time? Most of Earth's exposed surface is less than 2.5 million years old. Any evidence of civilizations millions or tens of millions of years in the past, beyond being eroded by time, would likely be deeply buried. The odds of finding direct evidence would be exceedingly low. We would be more likely to encounter indirect evidence, such as finding those pesky microplastics deep under the surface or in deep ice cores where our technology could not have penetrated.
Let's extend on that. Let's imagine that prior to one or more of the great extinction events - the Permian-Triassic extinction event 252 million years ago, the Triassic-Jurassic extinction event 201 million years ago, and/or the Cretaceous-Paleogene Extinction Event 66 million years ago - there was an industrial civilization peopled by intelligent relatives of the dominant forms of that time, a civilization that expanded into space and perhaps even to other systems before the destruction of the homeworld civilization led to the gradual collapse of that civilization's planetary and stellar colonies. Or perhaps that civilization never developed an interstellar drive and its survivors in space instead traversed between worlds on colony ships and eventually gave up travelling to the inner systems, instead roaming interstellar space and only grabbing resources from the distant Oort clouds of the various systems, escaping the notice of the inner system civilizations. Evidence for their past existence would be all but nonexistent on terrestrial worlds and so rare in space as to be discounted as misinterpretation or outright fabrication. A civilization based on interstellar drives might never realize there was a civilization thriving deep in interstellar space until some chance observation of a colony ship in the Oort Cloud by some astronomer willing to risk his reputation prompted someone to jump a ship out to investigate. And then, if the colony ship had sufficiently advanced drives, it might escape further scrutiny simply by running into deep space faster than the fastest ship could follow.
There's been enough fossil fuel on Earth since the end of the Carboniferous, 350 million years ago, to support an industrial civilization. If such a civilization existed on Earth, millions or tens of millions of years ago, what evidence of it might still exist after all this time? Most of Earth's exposed surface is less than 2.5 million years old. Any evidence of civilizations millions or tens of millions of years in the past, beyond being eroded by time, would likely be deeply buried. The odds of finding direct evidence would be exceedingly low. We would be more likely to encounter indirect evidence, such as finding those pesky microplastics deep under the surface or in deep ice cores where our technology could not have penetrated.
Let's extend on that. Let's imagine that prior to one or more of the great extinction events - the Permian-Triassic extinction event 252 million years ago, the Triassic-Jurassic extinction event 201 million years ago, and/or the Cretaceous-Paleogene Extinction Event 66 million years ago - there was an industrial civilization peopled by intelligent relatives of the dominant forms of that time, a civilization that expanded into space and perhaps even to other systems before the destruction of the homeworld civilization led to the gradual collapse of that civilization's planetary and stellar colonies. Or perhaps that civilization never developed an interstellar drive and its survivors in space instead traversed between worlds on colony ships and eventually gave up travelling to the inner systems, instead roaming interstellar space and only grabbing resources from the distant Oort clouds of the various systems, escaping the notice of the inner system civilizations. Evidence for their past existence would be all but nonexistent on terrestrial worlds and so rare in space as to be discounted as misinterpretation or outright fabrication. A civilization based on interstellar drives might never realize there was a civilization thriving deep in interstellar space until some chance observation of a colony ship in the Oort Cloud by some astronomer willing to risk his reputation prompted someone to jump a ship out to investigate. And then, if the colony ship had sufficiently advanced drives, it might escape further scrutiny simply by running into deep space faster than the fastest ship could follow.
