Was There a Civilization on Earth Before Humans? | Hacker News Reader

Was There a Civilization on Earth Before Humans?

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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.

A science fiction story set in this time would be truly epic and beautiful.

Truly. But a story which inevitably must end with expansion, cooling, and a new need to huddle around stars.

Our story inevitably ends with the Earth roasting and then freezing as the Sun ages. There’s still lots of good stuff to tell in the meantime.

The Integral Trees (Larry Niven, 1984) is about a society living in a ring of gas around a neutron star. Not quite the same, but a similar interesting astrophysical idea.

Space 1999 was a little like that. The premise was that the moon was blasted out of the Solar system into interstellar space. Somehow, the doughty denizens of Moonbase Alpha managed to encounter a new planet with intelligent life in nearly every episode. That would have required the stars to be pretty close.

Thanks for the reminder. I was completely OBSESSED with that show as a kid.

I seem to remember an episode in Stephen Baxter's "Evolution" where two dinosaurs discuss the idea of technical progress but were stymied by a catastrophic event.

Tau Zero by Poul Anderson is an interesting little novel that touches on some of this stuff.

We're kinda in the mid-game. We can still see __a lot__ of galaxies and can still reach them. The universe will keep expanding forever and at some point, the cosmic event horizon will shrink to the size of our galaxy. There is still a wide variety of stars including supergiants which can seed the galaxy with heavy elements when they go supernova. There will be a time when only Red Dwarves will survive, and after trillions of years the universe will enter a dark age when there are no stars with visible light left.

Do we really know that the expansive forces will continue forever? Is it possible we're living in milk spilled on the floor of some higher dimensional reality and at some point the "surface tension" will override the expansive forces?

This depends on the cosmological constant (dark energy). There are 3 scenarios: The big rip, the big crunch and equilibrium.

In the big rip scenario, dark energy will overpower all other forces and at some point space itself will expand so fast that the cosmic event horizon will be smaller than the smallest particle which means that nothing will be able to reach anything (even particles).

In the big crunch scenario expansion will stop at some point and it will reverse and in the end the whole universe will be concentrated in a point (just like before the big bang).

Equilibrium means that the expansion stops but does not reverse.

What do you mean by "surface tension"?

He’s probably referring to supergravity theory.

No, I am definitely not that informed on the subject :)

> What do you mean by "surface tension"?

I was making an analogy to the behavior of fluids in our reality. Really though, what I was getting at is, do we, or can we, really know the nature of the universe to such a degree that we can rule out behaviors which may change as the universe progresses through whatever sequence of events through which it is progressing? I think you answered my question, such as it was.

We don't yet know. Right now the consensus is that the universe will probably expand forever and will ultimately reach heat death. If the acceleration is accelerating though that means a Big Rip scenario, but it is very unlikely.

I am a fan of conformal cyclic cosmology. It sort of goes like this: Pick a spot, that's you. After the big rip, all other particles are beyond your hubble horizon, you can not affect them and they can not affect you. Its just you alone in the void, whiling away the aeons. This is a very low entropy state, just like the start of the big bang. So the very end is indistinguishable from the very beginning, and the cycle starts all over.

https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology

"after trillions of years the universe will enter a dark age when there are no stars with visible light left".

Ok but, armchair amateur here, the scale of space is not known to humans, right? We cannot comprehend the actual limit of the universe, can we? How can we know that the universe entering a dark age is not a local effect in our known universe, and that other, incomprehensibly distant parts of the universe will keep doing just fine?

For that matter, if the universe enters a dark age, what is it that caused the universe to be in a "light age" in the first place? There has be a force that causes the universe to exit a "dark age" otherwise it would always have been dark.

These kinds of things perplex me.

Not a physicist, but at a guess: Occam's Razor, plus the existance of simpler theories which explain our current observations.

I think this (Occam's Razor) clearly illustrates the limit of our perception/comprehension though. It is entirely possible that due to our comprehension of the complexity involved with dimensionality, we can be only vaguely aware (if at all) of a more complex system than the one we can perceive/comprehend. I'm reminded of the book Flatland[1].

It is fine to attempt to apply our rubrics, but I am not sure how to quantify the limits of our perception. Perhaps Occam's Razor and current simpler theories give a useful working tool for us to reason within our local known (or perceived/comprehended) universe.

The best way I can think of to ask this is, how do we factor in the "unknown unknown"? It is maddening not to be able to.

[1] https://en.wikipedia.org/wiki/Flatland

I mean, that's why people do theoretical physics in higher dimensions and then search desperately for ways to test their theories. We can extrapolate with mathematics in infinite ways, but until we can find ways to test things it's hard to do better than "find the simplest explanation that accounts for what you can observe".

Slightly off-topic, but how robust is Occam’s Razor as a principle for judging the likelihood of a theory being true?

Occam's razor is the search heuristic with bottommost priority. It works well because it's easier to falsify simpler things than more complex things. It's a technique to avoid adding epicycles and not very effective further up from there.

If you have other reasons to believe a more complex hypothesis may be likely those should generally override Occam's Razor.

I started typing a reply, but as usual Wikipedia has a better response than I do:

https://en.wikipedia.org/wiki/Occam%27s_razor#Justifications

This isn't the answer you're looking for, but I'm reminded of the book of Genesis:

> "[1:2] And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. [1:3] And God said, Let there be light: and there was light.

If you'd like to read more, here you go: https://www.blueletterbible.org/kjv/gen/1/1/s_1001

I will note that in the above it says "morning" and "evening". In some sense, the writing is old enough that we assume that is what the original hebrew meant, but we don't actually have context to say. I've heard that the word for "morning" (erev) could have meant "order", and "evening" (boker) could have meant "disorder".

So what you get is 7 days (depending on who you ask) where the second law of thermodynamics is "wound up", if you will, which resulted in an ordered universe that isn't just a homogeneous soup.

This quotation demonstrates that man has been pondering this same quandary for a great many years. How does one conceive of that which is out of our comprehension? This is where the fields of logic, philosophy, religion, science, etc. try to help build a model for understanding. However, I find that no model we have is sufficient to truly understand, not yet at least.

Religion may have started building a model for understanding - but has been failing for at least 5000 years.

> but has been failing for at least 5000 years.

I encourage you to take some time and study the Christian church during the Middle Ages. Much of what we consider 'modern' learning, teaching, and method came about because there were monks an nuns who were very serious about their work.

Likewise, I encourage you to study Islam since its inception; there also clerics (I don't know the proper terms) sought to increase understanding in literature an science some 500 years before the church in Europe.

Also take some time to look into various religious orders (Hindu, Buddhism, and others) throughout Asia that, in very similar fashion, worked to preserve and expand knowledge within their orders and in their surrounding communities.

If anything, religion has been a driving force towards foundational methods of understanding, knowledge acquisition, and preservation.

>So what you get is 7 days (depending on who you ask) where the second law of thermodynamics is "wound up", if you will, which resulted in an ordered universe that isn't just a homogeneous soup.

Please... please don't imply that the book of Genesis, or any similar religious work, holds some hidden insight into modern science. The authors of Genesis, whoever they were, did not know what thermodynamics was, and were not writing about it when they came up with the Genesis account.

> Please... please don't imply that the book of Genesis, or any similar religious work, holds some hidden insight into modern science.

I didn't. Nor was that my intent. I only wanted to point out that there was something interesting and relevant to the above post.

I would like to know from those who down voted my comment: why down vote?

My intent was to add an extra dimension to the conversation.

"dark age" is just something I came up with. By "dark age" I meant that there are no thermonuclear processes left providing light for us. After trillions of years the last Red Dwarf will run out of fuel and there will be no light-emitting stars left.

We don't know the scale, that's why we usually say "observable universe", but we do know the rules which apply everywhere.

"light age" or whatever you call it in this context means that there are still stars left which emit light.

After the "dark age" there will be the heat death of the universe.

Your comment prompted me to re-read The Last Question by Asimov (https://www.multivax.com/last_question.html).

Your comment prompted me to re-acknowledge my fear of mortality

Wow, I've never read that but I will do so now!

There's also "The Last Answer" by Asimov, and if you're into these types of stories I can also recommend The Egg (by the writer of The Martian).

I remember Étienne Klein explaining that one of the theory why the universe is flat (if you take 3 galaxies and draw a triangle using them as points the sum of the angles will always be 180) is that we might be like an ant sitting on a ball. The ant only sees so much of the ball and from its perspective everything is flat. But in reality the ball is round.

Or the ball is projected from a 3D surface infinitely far away :D (holographic universe theory)

There are two different effects at play here. On the one hand, there will be a dark age because all the stars will burn out. This has nothing to do with the cosmological event horizon.

The cosmological event horizon is caused by the accelerating expansion of the universe. Space is expanding uniformly, so the more space there is between us and some object, the faster it is moving away from us. Objects that are farther than the Hubble Distance from us are receding faster than the speed of light, and so their light will never reach us. Over time, everything that isn't gravitationally bound to us will recede into the distance, redshift and disappear, leaving only our galaxy within the observable universe.

Roger Penrose has speculated that the ultimate heat-death of one universe, the stage where space, time, radiation and matter lose all meaning is identical with the singularity from which a new universe emerges.

Obligatory mention of Asimov’s The Last Question. Give it a read if you haven’t! Phenomenal short story.

you post a small comment sometimes that opens a random person's horizon. thank you

glad you liked it :)

Note that heat death happens when the universe reaches thermal equilibrium (maximum entropy). It is theorized that sudden drops in entropy are possible which could have caused the big bang.

To be precise, the cosmic event horizon isn't shrinking: it will always remain at the Hubble Distance. However, everything that isn't gravitationally bound to us is receding from us at gradually increasing speed. The cosmic event horizon is the distance when that speed exceeds the speed of light, making it impossible for light to reach us. Just like an object entering a black hole, it will take forever for objects to actually cross the horizon, but they will smear out and redshift, becoming too faint to see, in some finite time.

Whoa. Now this is super interesting!

What is z in that paper?

First words of the abstract:

> In the redshift range 100<(1+z)<137, ...

z is the letter often used for redshift, https://en.wikipedia.org/wiki/Redshift, a stand-in for cosmological time that's easy to extract experimentally (as compared to an actual time). (1+z) is essentially the ratio by which the universe is bigger today than it was when the physics being observed happened.

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?

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.

How much stationkeeping does a geostationary satellite have to do to remain in orbit over a long time scale?

I would think not much?

I think none if positioned well enough.

Things like the moon will perturb it - orbits assume a 2-body system when we are strictly speaking in a (chaotic) n-body system.

Over millions of years that will add up, honestly I'm hoping someone else will do the math/research and figure out if they add up to enough that they wouldn't still be orbiting earth.

That’s my point though. The moon hasn’t degraded and crashed into the earth so it’s clearly possible for a satellite to orbit the earth indefinitely - for some suitable definition of indefinite.

The moon's stability is a good point, but not conclusive. The moon's orbit isn't perturbed by it's own gravity. It's also much larger, so much more mass (radius cubed)/surface area (radius squared), so less affected by solar wind, micro meteor impacts, and the like.

But still, it's more likely we'd find evidence of a distant past civilisation on the moon than on earth right?

The moon’s orbit is taking it further from Earth over time, it it’s very far away and very massive, as well as being influenced by the Sun. A satellite’s mass is almost negligible, and compared to the Earth-Moon distance it’s distance from Earth is too. A pebble hitting the moon also isn’t going to do much to change its course, while the same pebble will do a lot more to a satellite. The same is true of dust.

The moon has a ton of mass and—therefore—inertia. The chaotic effects of the system are still present, but require dramatically larger timescales to notice any kind of effect.

Anything sitting on the surface of the Moon would must likely completely buried by regolith after roughly 2 million years. Every lunar day dust particles are launched up from the surface only to fall back down at night.

Where do you get 2 million from? I.e. why not 20k or 200m?

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.

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...

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.

do you think large cities can exist without a record system ? or maybe we just have no traces of these records ?

Maybe a past civilization created a simulation we are living in.

What do you mean by past?

If we look like the Sims to them, the current player may find it funny that we refer to their Game Devs as being part of a past civilization, which could make them wonder if they're part of a sim...

The player downloaded the sim to a Universe Console, watched the big bang, eventually became bored and has moved on.

Assuming there's no "[Select] to skip cutscene", which reminds me of a Star Trek:Voyager episode (Blink of an eye https://www.imdb.com/title/tt0708856/)

if we are part of the sim, they are too

Maybe that's still ahead of us and there never will be sufficient data available for a meaningful answer.

Or, we're indeed in a simulation which is aimed to preserve the image of species that evolved beyond physical form eons ago.

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.

Don't forget that sea levels have risen some 120 meters since the end of the last ice age. Given that civilizations tend to form close to the ocean, most archeological evidence from tens of millennia ago, if such existed, would be under water.

http://theconversation.com/ancient-aboriginal-stories-preser...

> Homo sapiens started emigrating out of Africa 50k years ago.

Well new evidence suggests that humans colonised Aus around 65k years ago. There is also some evidence of human activity in the Americas thats far older, although the evidence is scant at the moment.

> There was no glaciation or sea change to destroy the evidences.

No sea level change? With the last glacial maximum the sea level was about 120m lower than now, wasn't it? Is it not reasonable to assume coast settlements or cities would now be submerged? There was continental-sized areas of land lost during that sea level rise. The amount of land lost in Asia alone is staggering.

> I believe there is no fact to sustain that hypothesis, and many facts against it.

Perhaps, but new evidence keeps on being discovered and lets not forget that lots of facts may simply be submerged under hundreds of meters of seawater.

Its fun to keep an open mind.

> If they had cities in Africa, it is very surprising we found no trace of it, given the numerous archaeological expeditions everywhere in Africa. > I believe there is no fact to sustain that hypothesis, and many facts against it.

At least these archaeologists beg to differ:

https://youtu.be/CBMretoTFJg?t=315

https://www.youtube.com/watch?v=yEtDLBGGQeQ

Even in Egypt stuff are still being (last pyramid discovered in 2008, a tomb buried under the sand last december).

The Sahara is approximately the size of the US and India combined, and we know it was still green during the Early Dynastic Period of Egypt. Lot of place for humans to settle, now all covered in sand.

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.

Well it will be The Ice People from René Barjavel

https://en.wikipedia.org/wiki/The_Ice_People_(Barjavel_novel...

Edit: if you are ever interested in reading it, the Wikipedia plot part reveals the whole story, end included

Thank you, for this.

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.

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.

https://en.m.wikipedia.org/wiki/Oldowan

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.

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?

You're assuming they didn't have an anti-gravity engine

They didn't, because anti-gravity is not a technology that can actually exist.

Why not?

Like FTL, nothing in physics as we understand it, or that we've observed in the universe, allows for even the possibility of anti-gravity. Theories always require some magical fudge-factor like "negative mass" that, as far as we know, don't really exist either, and can't apply to our universe.

As far as is known, the only way to generate gravity is mass, and the only way to counteract gravity is to push against it in the other direction hard enough, but that's just rocketry.

Then they would just use anti-gravity engine near any sufficiently massive body and generate as much energy out of nothing as they wanted...

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.

You don't need FTL to explore the entire galaxy in 1B years. The Milky Way is only 100k ly across, so your fleet would only need an average speed of .1c to see it all. E.g. a robot fleet with a program to "see all parts of the galaxy" would colonize, refuel and rebuild another fleet, and send it off to repeat, and easily reach the entire galaxy. (The tech we're missing is a way to turn solar power into anti-matter, then power your ships with slow trickle matter/anti-matter annihilation.)

Your last sentence is the premise of the novel Roadside Picnic

Possible - sure. But the default state should be to assume FTL aliens would need to refuel.

Consider human civilisation circa 3000 years ago. People moved around on horses, with carts. Roads were usually poor or non-existent. We are incomparably advanced compared to back then. But:

• They had outposts for travellers and we have airports.

• They had to feed their horses, we have to refuel planes.

• They needed infrastructure to establish new towns and colonies. We do too although the Earth being inconveniently full of cities often hides this fact.

Whilst the technology has changed enormously the fundamentals of travel and colonisation haven't. If there's no refuelling process at all ever then that implies a violation of the conservation of energy laws anyway - even if you only refuel once when a ship is newly built with some incredibly long lasting energy source, that's still fueling.

That's somewhat of an anthropomorphic bias that may or may not hold true and is impossible for us to determine until we meet said aliens.

> “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.

We're too similar to other life on earth for that to be credible.

We says we, the martians, didn't bring the other stuff with us?

Life has been on Earth for at least 3.8 billion years. All of the life on Earth today is descended from that original life. So if life on Earth originally came from Mars, it would have had to do so at least 3.8 billion years ago. But that's too close to the origin of the solar system as a whole for it to be credible that an industrial civilization could have evolved on Mars, caused a climate catastrophe, and then migrated to Earth.

I don't think it's at all likely that life on Earth originated on Mars, but if it did then there could have been cross pollination of microorganisms over billions of years due to meteor impacts on both worlds throwing bits of crust into space. In fact if we do find life on Mars at some point it wouldn't be shocking if they are quite similar to bacteria found on Earth, since they might just be descendants of earth bacteria carried over from the impact that killed the dinosaurs.

Or ok the flip side perhaps life originated on mars or europa or even interstellar, with single cells organisms coming from there

> if it did then there could have been cross pollination of microorganisms over billions of years

I don't think this is consistent with DNA evidence, since such cross pollination would be expected to show up as two sets of genetic lines of descent with very different characteristics, since the environment of Mars is very different from that of Earth; and we don't observer anything like that. In fact, if life was evolving separately on Earth and Mars, it might not take very long before the two lines of descent were not even compatible genetically, meaning that genetic exchange would be impossible even if the organisms were brought back together.

I just thought of that that argument only holds water if there wasn't exchange of genetic information between the planets. If during evolution cells and viruses get blasted from one planet to the other on a regular basis, that would not be a great argument.

It would have had to have been going on long before intelligence arose though, which is not impossible.

Venus makes much more sense in the comparison,

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.

> If they could terraform another planet, they could probably just fix mars instead.

So why do humans find it easier to conceive of terraforming Mars, than to just fix our planet instead?

Terraforming Mars is more adventurous and romantic.

It's the same reason that software engineers love greenfielding projects. Architecting clean, fresh systems is romantic! You won't make any of the mistakes that you've now learned from! All this needless complexity can be done away with once and for all.

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.

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.

Hence suggesting it’s more than just brain size that leads to civilization.

Edit-this is also why I’ve never considered the threat of a singularity creating a malevolent super-AI to be serious. Larger brains do exist on earth and they only kill humans rarely.

in "the science of discworld"[0] this is touched upon through the nice example of: T-Rex have been on the planet for a few million years, they were huge, and we found a handful of their fossils. It is plausible (but not probable) that a civilization of smart lizards evolved and disappeared in 100k years without leaving any trace that we could find.

[0] https://en.wikipedia.org/wiki/The_Science_of_Discworld

You have to look at the brain-to-body mass ratio, but even that is not accurate by itself, you have to look at the encephalization quotient for a more accurate measure.

As per the wikipedia's page on brain-to-body mass ratio.

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.

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.

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?

Ive heard there is too much oxygen in the air now for the original oil forming processes

> there is too much oxygen in the air now for the original oil forming processes

This is addressed in the article:

“...our work also opened up the speculative possibility that some planets might have fossil-fuel-driven cycles of civilization building and collapse. If a civilization uses fossil fuels, the climate change they trigger can lead to a large decrease in ocean oxygen levels. These low oxygen levels (called ocean anoxia) help trigger the conditions needed for making fossil fuels like oil and coal in the first place.”

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.

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.

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.

Maybe Humans?

Maybe parrots?

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.

[0] https://www.youtube.com/watch?v=_-sTbaH-aA0

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!

[1] http://www.scp-wiki.net/scp-1115

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.

I really enjoyed the whole Giant series by Hogan.

Star Trek Voyager had an episode with the idea of an ancient saurian species that left earth many millions of years ago. https://en.wikipedia.org/wiki/Distant_Origin

Did that come first or did Doctor Who do it first?

I think TNG's The Chase is yet more interesting; it's also a shame its plot was never pick up again by series creators. https://en.wikipedia.org/wiki/The_Chase_(Star_Trek:_The_Next...

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