If the paleocene-eocene thermal maximum was caused by an industrial civilization predating ours, how would we tell? Would we expect such a civilization to leave an extensive fossil record? Even in the face of subsequent glacial advances and retreats and sea level changes?
Bones are tough stuff, yet aren’t preserved except in very rare conditions. I expect most of our technology would be similar. Big landscape-altering projects like roads should leave marks for longer–but fifty million years is enough time for some serious erosion,especially at latitudes subject to repeated glaciation. But sea levels were higher in the period immediately prior, so I guess if the Great Amphibious Squid Civilization were building cities on land, we would stand a chance of finding it. But man, how funny would it be if we got to Mars and found the GASC had left a plaque saying “blorp blorp we came in peace for all squidkind blorp”
I’ve seen common transparent silicate glass being mentioned as something that would be a dead giveaway of the presence of such an industrial civilization even across timeframes that long; it is commonly present pretty much everywhere where modern-type industry exists, it is quite hard and very resistant to chemical corrosion, and as such it would seem rather likely for glass shards to be able to survive being buried in sediment for long periods of time, probably more so than, say, bones or steel. It is also not very similar to any natural material that I’m aware of - natural glass like e.g. obsidian is generally not very transparent and doesn’t usually come with flat surfaces, and natural transparent materials are typically strongly crystalline in a way that glass is not.
This, the nuclear power thing, and the accessible metal deposits in that Overcoming Bias link seem to be the main things. Although with metals/fossil fuels, I think it would be hard to exclude the possibility that they were once *even more* abundant, or more abundant in locations where they’re now absent. Do 50 million year old empty crude oil reservoirs leave a distinct geological trace we could test for?
(via tanadrin)


