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> but does that mean xenoarchaeology My favorite "crazy theory" is that the Paleocene–Eocene Thermal Maximum (PETM) was caused by a previous industrial civiliz

> but does that mean xenoarchaeology My favorite "crazy theory" is that the Paleocene–Eocene Thermal Maximum (PETM) was caused by a previous industrial civilization that, like us, found a bunch of easy to access hydrocarbons, naively dug them up and reached the same climate change problem that we did, ultimately wiping them out. Of course there is 0 evidence for this at all, but it was also more than 50 million years ago. If you look into it basically nothing about an advanced industrial civilization would likely survive to make it into the geological record for us to observe. The only reason to even entertain this hypothesis is that the PETM also experience a very rapid increase in atmospheric CO2 and we aren't entirely sure why. Unfortunately this means that there's probably not much chance for a rich field of xenoarchaeology to exist since it's not even possible to do this on our own planet. What is an interesting thought experiment is: Suppose we realized we as a civilization were doomed and wanted to sent a message to future industrial civilization on Earth warning them about being too aggressive with hydrocarbon usage. To my knowledge there is no known method to ensure a message could be sent that far in the future, but it's fun to try to think of ways we could send a message to a future, essentially, alien civilization here on Earth.

brian_cloutier 3y ago
Why would they have left no traces? Dinosaurs lived ~200 M years ago and left enough traces for us to discover them. Wouldn't an industrial civilization 50 mya have left some kind of refined metallic artifacts? Even if _most_ traces are eroded away with time it seems difficult to imagine every trace of a global industrial civilization would disappear. There also don't appear to have been any spikes in atmospheric carbon dioxide during the relevant period: https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere#Concentrations_in_the_geologic_past https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at... Though maybe you were looking at a data source with better resolution?
- dadoomer 3y ago
  The answer is that the traces are not super easy to find, depending on how we characterize what traces are in the first place. The question posed is known as the "Silurian Hypothesis": https://www.scientificamerican.com/article/could-an-industrial-prehuman-civilization-have-existed-on-earth-before-ours/ https://www.scientificamerican.com/article/could-an-industri...
secant 3y ago
> Unfortunately this means that there's probably not much chance for a rich field of xenoarchaeology to exist since it's not even possible to do this on our own planet. I think you've reached this statement too eagerly but would be interested to discuss this point. Do you mean that the materials they used would have disintegrated and their (presumably carbon-based lifeform) bodies wouldn't have left any fossils? My main thoughts on this come from reading Vernor Vinge's [1] excellent Marooned in Realtime which discusses some of the condundrums resulting from transferring information over massive periods of time. I think part of it talks about subduction zones where everything is eventually riven back into the Earth's mantle, essentially lost to any kind of current archaelogical techniques. [1] https://en.wikipedia.org/wiki/Marooned_in_Realtime https://en.wikipedia.org/wiki/Marooned_in_Realtime
smiley1437 3y ago
Good point! The longest-lived artifacts would probably have to be somewhere with much less weather and geological activity than the surface of the earth. Maybe if you put a structure in orbit or perhaps on the moon? Paradoxically, extending on your thought - I guess anywhere with living conditions similar to earth (oxygen atmosphere, water, weather, etc) would not be conducive to long term archival of civilization artifacts. So you'd have to look at 'dead' places if you want to find evidence of civilization. Or stumble across an derelict megastructure (dyson sphere\niven ring\etc)
- adastra22 3y ago
  Many surfaces of the Earth are eroded away over that timescale, but not all. Otherwise we would be be able to dig up dinosaur bones.

brian_cloutier 3y ago

Why would they have left no traces? Dinosaurs lived ~200 M years ago and left enough traces for us to discover them. Wouldn't an industrial civilization 50 mya have left some kind of refined metallic artifacts? Even if _most_ traces are eroded away with time it seems difficult to imagine every trace of a global industrial civilization would disappear. There also don't appear to have been any spikes in atmospheric carbon dioxide during the relevant period: https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere#Concentrations_in_the_geologic_past https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at... Though maybe you were looking at a data source with better resolution?

dadoomer 3y ago
The answer is that the traces are not super easy to find, depending on how we characterize what traces are in the first place. The question posed is known as the "Silurian Hypothesis": https://www.scientificamerican.com/article/could-an-industrial-prehuman-civilization-have-existed-on-earth-before-ours/ https://www.scientificamerican.com/article/could-an-industri...

secant 3y ago

> Unfortunately this means that there's probably not much chance for a rich field of xenoarchaeology to exist since it's not even possible to do this on our own planet. I think you've reached this statement too eagerly but would be interested to discuss this point. Do you mean that the materials they used would have disintegrated and their (presumably carbon-based lifeform) bodies wouldn't have left any fossils? My main thoughts on this come from reading Vernor Vinge's [1] excellent Marooned in Realtime which discusses some of the condundrums resulting from transferring information over massive periods of time. I think part of it talks about subduction zones where everything is eventually riven back into the Earth's mantle, essentially lost to any kind of current archaelogical techniques. [1] https://en.wikipedia.org/wiki/Marooned_in_Realtime https://en.wikipedia.org/wiki/Marooned_in_Realtime

smiley1437 3y ago

Good point! The longest-lived artifacts would probably have to be somewhere with much less weather and geological activity than the surface of the earth. Maybe if you put a structure in orbit or perhaps on the moon? Paradoxically, extending on your thought - I guess anywhere with living conditions similar to earth (oxygen atmosphere, water, weather, etc) would not be conducive to long term archival of civilization artifacts. So you'd have to look at 'dead' places if you want to find evidence of civilization. Or stumble across an derelict megastructure (dyson sphere\niven ring\etc)

adastra22 3y ago
Many surfaces of the Earth are eroded away over that timescale, but not all. Otherwise we would be be able to dig up dinosaur bones.