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This reminds me of "The Habitable Epoch of the Early Universe" https://arxiv.org/abs/1312.0613 where it is pointed out that for some time during cosmological evolution, the universe would have been quite comfortable and rocky planets (if any existed) could have had liquid water, with no need to be in a Goldilocks zone---the whole universe was Goldilocks!
Back then everything would have also been so much closer together. The universe could have been like one great bustling city. Perhaps, from that perspective, we are already in some long-tail end-of-days time. Planets and stars and galaxies are so far apart as to make travel difficult or impossible.
Whoa. Now this is super interesting!
What is z in that paper?
Would geostationary satellites from a previous civilization still be orbiting in an approximately geostationary orbit? Or would they have been perturbed enough that they would either exit earth orbit or impact earth? Or pounded into dust by collisions?
If a previous civilization had metal-based moon landers, would we likely have found them/found areas with an unlikely amount of metal on the moon? Or would they have probably been obliterated by meteorites by now?
Have you seen Battlestar Galactica, the 2004 series ending to be exact? The Colonials after long and "bumpy" journey arrived on our Earth and in order to start anew they decided to abandon all technological advancements by setting their fleet on a collision course with the Sun.
We can't exclude the possibility that previous civilization also decided or was forced to abandon all its technology due to reasons known to them - that is, if they were enough advanced to have space-reaching technology.
It depends? If the satellites used chemical rockets to produce stationkeeping thrust then they’d be long gone, but if they used some exotic power source who knows? If they had a good AI and power, there is no real limit on how long they could stay in orbit. If they were using technology like ours they’d be gone, but a hypothetical civilization might use exotic materials and power sources that would stand the test of time.
For the moon thing, the above applies, but assuming that they were obliterated we’d have to get pretty lucky to detect their remains. They could also be totally intact because there would be essentially no weathering, they would never be buried by shifting regolith, and so on.
A geo-stationary satellite can stay in orbit for billions of years. I’m surprised this was not mentioned in the article at all.
Online version of the original paper:
"The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record?"
https://www.cambridge.org/core/journals/international-journa...
What interests me is the possibility of human civilizations between the Eemian and last glacial maximum.
Any evidence of civilization from that period would either be hella deep under the sea or obliterated by glacial expansion and retreat.
Homo sapiens have been here 300k years. I find it ridiculous to assume we only started living in cities about 5-7000 years ago. Conveniently the period immediately after the last rapid glacial retreat...
Homo sapiens started emigrating out of Africa 50k years ago. There is a small incertitude on their emigration pattern (one wave or several), but it doesn't matter here. If they had cities in Africa, it is very surprising we found no trace of it, given the numerous archaeological expeditions everywhere in Africa. There was no glaciation or sea change to destroy the evidences.
So according to your hypothesis, civilizations would have emerged from hominids other than the homo sapiens, contrary to what we know about them. And their cities would all be in the North of Europe, where the later glaciation could hide some archaeological proofs. And we could not detect anything, though an Ice age doesn't destroy anything.
I believe there is no fact to sustain that hypothesis, and many facts against it.
There is some consistent evidence for the current timelines for human civilisation - although it's all sketchy.
- complexity and type of tools & technology dug up - change in pollen due to agriculture - change in genetics of domesticated animals
None of these (as far as I know) point to cities or civilisations that didn't have cities (if such a thing is conceivable, which it could be) way further back than the current records show.
There’s no evidence I’m aware of for large cities from that long ago, but as you said there were certainly people! I would love to have a time machine and see what the languages and cultures were like from back then. Considering how much English has changed in the last thousand years, it’s mind boggling to think of how many cultures and languages could have come and gone in 300,000 years.
Maybe a past civilization created a simulation we are living in.
or maybe such an ancient city could be preserved under the polar ice caps, perhaps with ancient humans and their technology. and revealed by deep geothermal heat creating cavities under the ice, if only the cavities were explored.
I know they are focused on markers of industrial civilizations, but the prevalence of purpose built stone tools millions of years ago still blows my mind a little.
I always chuckle (and wonder at the veracity) when I find stuff like this: http://www.s8int.com/page8.html
It makes me wonder if the Ancient Aliens guy might be partially right.
Perhaps dolphins are descendants of an ancient civilization, they evolved from land animals https://www.whalefacts.org/dolphin-adaptations/
about 50 million years ago. Just imagining here, but what if they had an industrialized civilization that caused global warming that led to the PETM temperature rise, their civilization declined and they had to adapt to a water world. Chuckle, just a kooky thought I had after reading that article.
Alan Weisman's "The World Without Us" is an interesting book/thought experiment that highlights just how fast the features and evidence of a civilization might be erased through natural processes.
https://www.goodreads.com/book/show/248787.The_World_Without...
I'm actually more interested in if there was ever some sort of extraterrestrial outpost on this planet in the past 1 billion years or so.
At that time scale, exploring the entire galaxy seems reasonably practical. And stopping here to refuel and recuperate, not so unlikely, at least to me.
It's possible that the kind of extraterrestrial beings that could do any form of FTL travel wouldn't even think in terms of "outposts" or "refuel." The task is so immense that any technology capable of doing it would belong to a society that would be gods to us. You're treating it like it would be them cruising route 66, but for them, it could be something like us browsing a web page or even just dreaming. I dream I want to be on earth, and here I am.
A lot of SF is really bad in they assume people will be the same and just drive to different galaxies instead of drive to different states. But the technology between the two is so huge that to get there would probably entail a whole host of things that would transform them into something above us as mayflies are to us. Not sure we'd even be able to tell if they left anything or even stopped by.
Wouldn't it make more sense to acquire fuel from bodies with weaker gravity, so that you don't have to burn as much of it to get the rest back into space?
> “Wait a second,” he said. “How do you know we’re the only time there’s been a civilization on our own planet?”
Imagine for a moment that we're Martians who managed to terraform Earth because of some runaway climate catastrophe on Mars. That now, we're in the early stages of repeating the same mistakes because of some extinction event in the past that wiped out all of our prior history and knowledge.
If they could terraform another planet, they could probably just fix mars instead. There are a lot of weird contradictions in these kind of stories. Like they can move an entire planet's worth of people, but can't make a data repository that would survive them. Or that they would have a bad climate on mars, but somehow survive long enough to learn how to terraform a whole planet reliably as well as cross solar-system level distances.
We're too similar to other life on earth for that to be credible.
Venus makes much more sense in the comparison,
This reminds me of the great short story "The Next Ten Billion Years" by John Michael Greer: http://archdruidmirror.blogspot.com/2017/06/the-next-ten-bil...
I liked this part from the "10000 years from now" section
believers in most traditional religions declare piously that the climate changes of the last ten millennia are the results of human misbehavior, while rationalists insist that this is all superstition and the climate changes have perfectly natural causes.
My best reasoning for why we may conclude we’re the first civilization here is the brain sizes seen before us in the fossil record other biological features. You need big brains (in absolute volume), tool use, and culture forming. Of course, just a guess.
Crows and parrots seem to have roughly as many neurons as some of the bigger-brained primates, despite being a small fraction of the volume; that's how crows can, for example, make and use tools.
If you were a waterworld hyper-squid making this comment, you might be arguing that no life form with neurons measuring only microns in diameter could possibly respond fast enough to environmental stimuli to behave intelligently. We, with our myelinated neurons, know better; squid neurons aren't myelinated and do in fact need to be humongous to transmit signals quickly, but our myelinated neurons don't.
If there was some kind of apparatus capable of signal-processing, control, homeostatic feedback, language and visual processing, and at times seemingly intelligent behavior, while using switching and storage elements only tens of nanometers in diameter, which operate a million times faster than the switching and storage elements in your head (assuming you're a human), you might see the flaw in your inference. That's about twelve orders of magnitude denser processing power per unit volume: six orders of magnitude higher speed and six orders of magnitude lower volume. Of course, a hypothetical alien signal processing device that small (call it an "omvindnojm") might only be capable of very simple operations compared to a neuron, but maybe several of them together could be a feasible substitute?
Naw, who am I kidding? Such a thing is probably impossible. Your mammalian neurons are as good as it gets, kid.
Interestingly birds (and by extension some dinosaurs?) have brain structures that are much denser than mammals and therefore may have different correlations of intelligence to brain size.
Well, humans are not the ones with the biggest brain volume right now, but the question stands: why other animals have not evolved bigger intelligence before.
Weren't hadrosaurs in the running?
This reminds me of a couple of old sci-fi series I read a long time ago. Michael Moorcock's The Dancers at the End of time series about the last of humanity that's become apathetic, decadent and godlike as all the stars die around them and they come up with a plan to travel back in time and start civilization earlier so humanity get get on its feet quicker, but discover time is cyclical.
And another series, I wish I could read again but cannot remember the author or titles, but it was about a world where civilization ended because we'd genetically engineered ourselves and animals and everything into fairy tale creatures who overran everything. The whole time it seems like it's set in the future but it ends up the main characters become Adam and Eve and it implies all our current mythology came from the society that genetically engineered themselves out of existence.
I think Neanderthals buried their dead and looked after their elderly @ shanidar cave site. Does this imply civilization?
I think it implies a sophisticated culture, but people say that civilisations are those cultures that create cities. It's a narrow conceptualisation, but it goes hand in hand with the capabilities to create technologies that significantly modify the environment in favour of the members of the culture doing the city building. I don't think that anyone has found any indication of Neanderthals using any sort of pottery, agriculture, domestication or metalwork. This is not to say that they didn't have poetry and mathematics and understandings of the world we would find interesting and unexpected, or that they didn't have any of these technology - it's just that there is no evidence at all that I am aware of.
> And then there’s all that plastic ... creating a layer that could persist for geological timescales.
Won't the plastic eventually turn back into oil, on geologic timescales? Or are the conditions for that too specific to be relied on? Or am I completely mistaken, and oil->plastic is basically one-way?
Also it assumes our hypothetical prehistoric civilization took the same technological path we did and developed plastic or if it did used oil derived hydrocarbon monomers like we do.
Also there are microorganisms that digest plastic. They could've thrived at some point and then diminished in numbers after much of the plastic from the previous industrial civilization was consumed.
Ive heard there is too much oxygen in the air now for the original oil forming processes
If there was a civilization 50 million years ago, I would think some parallel species or genus would continue that DNA lineage to this day.
Somewhat incidentally, I was watching a Wisecrack episode on the philosophy of Tolkien which seemed to imply that his middle-earth universe was meant to be read as preceding our own history [0]. Following in that vein, I wonder what a high fantasy story that used prehistoric motifs would be like. Not a sci-fi story, actual fantasy. Instead of a high fantasy with elves and hobbits, maybe one with neanderthals and cro-magnons, but show them as having advanced, competing civilizations to homo sapiens. Maybe instead of increasing technical progress, we see primitive technologies evolve into living things like plants and animals. "Every sufficiently advanced civilization is indistinguishable from nature" as someone once wrote. Idk, I guess this doesn't add to the discussion, but it's stimulating to say the least.
I always liked this aspect of H.P.Lovecraft’s Chthulu mythos i.e. the allusion to the existence of pre-human civilisations (specifically in ‘Hyperborea’).
SCP-1115 [1] is proof!
Well don't all the megalithic sites which are all over the planet suggest exactly that?
"Inherit the Stars" by James Hogan is a good scifi story about this.
Also "The Hab Theory" by Allan Eckert.