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playing the advocate of the devil here, maybe the civilizations cleaned it all up and went solarpunk just before they transcended and vanished...

pavel_lishin 10y ago
Second time I get to mention David Brin in this submission! You might enjoy his Uplift series; it deals with scenarios not unlike what you mention.
InclinedPlane 10y ago
Basically an impossible task, and why would they? Imagine how hard it would be to completely cover up the evidence of human existence on Earth, for example. You'd have to find and excavate every single arrowhead out of the Earth, every single bit of plastic from the ocean. You'd have to figure out something to do about all the mines. You couldn't just fill them up, that would leave evidence. And even that would just be scratching the surface. Creatures complex enough and with big enough bodies and brains to potentially evolve into something that might build a technological civilization have only been around on Earth for a couple tens of millions of years, which isn't very long in geological terms. We don't see any evidence in the fossil record of ancient big brained creatures developing, and that's pretty much a pre-requisite for a technological species. There aren't any candidate creatures in the fossil record that could have conceivably evolved into a technological species in only a few million years, which means it would take a very big gap in the fossil record to have zero clues about such a thing, if it did happen. Also remember that fossil fuels are part of the fossil record, so we can be pretty confident that they didn't use fossil fuels. And, as mentioned, if they'd ever developed nuclear technology we would know about it, because the isotopic signatures from either their mining activities, enrichment activities, the operation of their reactors, or the above ground testing or use of nuclear weapons would be like a beacon. So, absent Slartibartfast levels of world-making or re-making, it's not a plausable theory, even as a stretch. Overall it would only make sense if they never used fossil fuels, never mined, never developed nuclear technology, never cut down forests, never had farms, never left behind artifacts made out of bone, metal, stone, ceramic, glass, plastic, etc, never modified the landscape in any way. And never had any evolutionary predecessors that left a fossil record. If you can figure out how to squeeze a plausible technological civilization into those constraints, good luck.

pavel_lishin 10y ago

Second time I get to mention David Brin in this submission! You might enjoy his Uplift series; it deals with scenarios not unlike what you mention.

InclinedPlane 10y ago

Basically an impossible task, and why would they? Imagine how hard it would be to completely cover up the evidence of human existence on Earth, for example. You'd have to find and excavate every single arrowhead out of the Earth, every single bit of plastic from the ocean. You'd have to figure out something to do about all the mines. You couldn't just fill them up, that would leave evidence. And even that would just be scratching the surface. Creatures complex enough and with big enough bodies and brains to potentially evolve into something that might build a technological civilization have only been around on Earth for a couple tens of millions of years, which isn't very long in geological terms. We don't see any evidence in the fossil record of ancient big brained creatures developing, and that's pretty much a pre-requisite for a technological species. There aren't any candidate creatures in the fossil record that could have conceivably evolved into a technological species in only a few million years, which means it would take a very big gap in the fossil record to have zero clues about such a thing, if it did happen. Also remember that fossil fuels are part of the fossil record, so we can be pretty confident that they didn't use fossil fuels. And, as mentioned, if they'd ever developed nuclear technology we would know about it, because the isotopic signatures from either their mining activities, enrichment activities, the operation of their reactors, or the above ground testing or use of nuclear weapons would be like a beacon. So, absent Slartibartfast levels of world-making or re-making, it's not a plausable theory, even as a stretch. Overall it would only make sense if they never used fossil fuels, never mined, never developed nuclear technology, never cut down forests, never had farms, never left behind artifacts made out of bone, metal, stone, ceramic, glass, plastic, etc, never modified the landscape in any way. And never had any evolutionary predecessors that left a fossil record. If you can figure out how to squeeze a plausible technological civilization into those constraints, good luck.