One of my commonly made arguments against the likelihood of finding extraterrestrial intelligence is that it seems to be remarkably rare on our planet — I’m not making a joke about Republicans (although I could), but am stating a fact, that in the half-billion year history of animal life on Earth, only one species has followed the evolutionary strategy of extreme reliance on technology, ours. It doesn’t seem to be a common way for complex multi-cellular organisms to succeed, so we should expect that even if that kind of life is common on other worlds, it’s not likely to produce organisms we can talk to.
But what if I’m wrong? What if intelligent life had arisen on Earth multiple times? Would we be able to recognize it in the geological record?
Forget about the SF tropes of finding the equivalent of the Statue of Liberty on a beach somewhere, or digging up a transistor radio. All the monuments and all the toys we’ve built would be crumbled away and ground into dust in a million years or so. But what about chemical traces? We’ve been pumping out all kinds of novel chemistry, maybe some bits of it would leave a signature behind for our successors to discover.
That’s the question asked in this article by Schmidt and Frank. What should we look for?
If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.
Like they say, there’s a fair amount of uncertainty — on a geological scale, we don’t know how long industrial byproducts will linger. Stuff like plastics and halogenated organics might persist for a long time, in the right environment, such as after being buried and sequestered. Maybe we should look in ancient sediments for compounds that are likely to have been produced by a technological society.
In a real twist, the authors also wrote a science fiction story about such a search. What if we found PCBs and transuranic elements in a deep stratum, and what if it was also associated with an abrupt change in climate or the biota of the time? How would scientists interpret that?
What I found most chilling, though, was the long list of unexplained, abrupt climate shifts they describe in the geological record. Worst case scenario: what if they were all caused by the appearance of species that achieved some kind of global dominance (not necessarily technological) that led to a brief period of self-defeating triumph that always led to their inevitable extinction?
I think I just gave myself nightmares. What if we launched a SATI (Search for Ancient Terrestrial Intelligence) program, found multiple instances, and learned that our peculiar niche is more common than we thought, and always leads to our decline and disappearance? Would that knowledge allow us to change, do better, and escape our doom, or would it tell us that any attempt would be futile?
Worse than finding Cthulhu would be finding it’s traces, and learning that it was long dead, it’s annihilation pre-ordained by its nature, as we will be.
Schmidt GA, Frank A (2019) The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record? International Journal of Astrobiology 18(2): 142-150.