If There Had Been a Mesozoic Civilization, Would We Notice?

[Vinyadan]

By civilization, I mean creatures with human-like capabilities, when it comes to socializing, transforming the environment, and making artifacts. Stone-Age men did a lot of things. They probably felled trees, hunted, wore clothes, build themselves homes... But we don't have much material about them. While stone and, sometimes, metal can hold on against time, organic materials like wood and leather are easily destroyed. Paint disappears over the ages; even Greek statues were brightly coloured, and that wasn't that long ago. Painting has survived inside of caves, where they were protected against the weather, but I tried looking for information about how long a cave can exist, and I didn't find much beyond "we don't really know" and "hundreds of thousands to a few million years". If a Mesozoic civilization had existed, and it had lived in caves, those caves could hold no remnants of their staying there, or have been blocked off, or collapsed, or disappeared.

Then we have the problems that arise when identifying artifacts outside of their stratum. Archaeologists have problems with artifacts from classical antiquity. Would we notice, if a hand axe (https://en.wikipedia.org/wiki/Hand_axe) were to come up from an utterly wrong stratum? Or would we just say, "well, I wonder how this got here!", and chalk it up to strange coincidences?

Probably, the two best chances for noticing would be finding stone carvings representing fauna that we can recognize, or finding a bodily remnant bearing artifacts. Maybe signs of ritual burial. But, even for humans, there aren't many cases in which burial allows for such long a conservation, with the probable exception of the unlucky folks who turned into bog bodies.

What do you think? When I was little, I was fascinated at the idea of some troödont-like dinosaur evolving into human intelligence. Now, thinking again about it, it might be like expecting an ostrich to build the pyramids, but it's still fascinating.

[VoxRationis]

We'd be more likely to notice the fossilized remains of the builders, I would think, or those of their near-sapient ancestors if we generously say that the civilization universally developed cultural practices that preclude fossilization.

[NRSASD]

Full disclosure: I am an archaeologist by training, but still very new to the field. Take everything I saw with a massive heaping of salt and skepticism.

I'd be very surprised if we hadn't noticed something by now. Besides material evidence (ie tools, clothing, etc.), there's tons of other things we ought to have seen by now. Injury patterns on bones indicating that they were struck by tools, not teeth or claws. Old, severe injuries that were healed, indicative of a support structure for wounded members of their society. Fire pits. Shaped stone or wood. Collections of beads. Mixing of dissimilar species (think sheep and shepherd).

From personal experience, we can identify dirt floors in ancient structures because the soil levels are completely different in how they look and function. A floor has been deliberately packed down and is quite dense, while any debris that settled on top of it is loose and easy to move. I'd imagine this would show up in the fossil record as well if it were there.

It's always possible we just haven't found the evidence yet, but if this sentient species were anything like humans I suspect it would have spread across a wide geographic area. We should have seen something suspicious by now if there was anything to find.

My vote: If there had been a sentient species that behaved anything like humans did, we probably would have found it by now. That being said, we have only found a finger bone and 3 teeth from one of our nearest cousins, the Denisovans, who disappeared a mere 30k-50k years ago.

[thorgrim29]

The was a pretty interesting article about that very subject a few week ago on The Atlantic. The gist of it as far as I could figure it out is that post industrial revolution our sediment layers will be very weird (lots of nitrogen, odd carbon isotopes, rare earths showing up all over the place, etc..) and that might be a clue but a society that never got to that point would be all but impossible to detect.


https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/

[wumpus]

The was a pretty interesting article about that very subject a few week ago on The Atlantic. The gist of it as far as I could figure it out is that post industrial revolution our sediment layers will be very weird (lots of nitrogen, odd carbon isotopes, rare earths showing up all over the place, etc..) and that might be a clue but a society that never got to that point would be all but impossible to detect.


https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/

Of course, the whole bit about the "meteor killed the dinosaurs" theory is that there is tiny sliver of weird (presumably from the asteroid) elements exactly at the K-T boundary. So if a civilization rose up and destroyed itself, all the pollution should be found in that boundary. I wonder what type of process fills the atmosphere with iridium (the oddball element in the K-T layer which is presumably leftover meteor).

Humans have only had a few millenia of civilization that barely scratched the planet, all of that could easily be covered over in a few million years. We've only had a few decades of technology capable of wiping ourselves off the planet. I'd expect the "human catastrophe" boundary left for the next civilization will look a lot like the K-T boundary.

On the other hand, if we encounter leftover spacecraft parts in space, they might have come from Earth in the deep past and not elsewhere. Note that I don't think any orbit is stable for a hundred years (check the Lagrange points, they are the exception). Anything in low Earth orbit decays in centuries, while anything up high (like geosync) gets batted around by the Moon until it is ejected, hits the Earth (or enough atmosphere to bring it in over thousands of years), or winds up hitting the Moon or entering Lunar orbit.

[factotum]

Full disclosure: I am an archaeologist by training, but still very new to the field. Take everything I saw with a massive heaping of salt and skepticism.

The things you're talking about as being things that we ought to have found are all things that I'm pretty sure wouldn't last 60 million years, as they'd have to in this case. The one area where I agree with you is stuff that's preserved in the bones, so we'd have found them in fossils--signs of bones repaired using medical techniques, bone injuries caused by weapons, and of course a skull cavity big enough to contain a brain capable of human-like levels of reasoning, all ought to have been discovered by now if they were there to find.

[jayem]

The things you're talking about as being things that we ought to have found are all things that I'm pretty sure wouldn't last 60 million years, as they'd have to in this case. The one area where I agree with you is stuff that's preserved in the bones, so we'd have found them in fossils--signs of bones repaired using medical techniques, bone injuries caused by weapons, and of course a skull cavity big enough to contain a brain capable of human-like levels of reasoning, all ought to have been discovered by now if they were there to find.

Though a lot of fossils are quite partial (to the extent that a lot of species are known by a tiny part). Fossilisation selects those that die in unusual places (e.g. floods and mudslides). And the Cretaceous alone is longer than the time since (or if the fictional civilization lasted 800,000 years, 99% of the fossils would miss it).
At which point it's at the level where it would be a bit of a toss up.

[Andor13]

It depends. What do we mean by civilization?

If you mean an agrarian utopia, then there could have been a dozen, and we'd have to basically stumble across a perfectly preserved settlement ala Pompei to know about it. If you mean a technological civilization, then, yes, it's possible there could have been one and we have yet to find the signs. According to the recent article on the subject there is an ironic effect that the more sustainably a civilization lives then the harder they will be to detect, because it's the extreme suddeness of the shifts, along with the weird chemical distributions that we create that are the hallmarks of the anthropocence. So a less aggressively progress seeking species would have a more gradual impact and be harder to detect. Likewise a less expansionist species (or otherwise geographically limited one) could easily produce such a small foot print that we'd need the devils own luck to stumble across them.

Consider the aliens of David Brin's Uplift War series. They plan for the extremely long term and are generally of a conservationist bent. They tend to deliberately build their cities on tectonic subduction zones so as not to interfere in the future development of the planets they visit. Such a species could have visited the Earth, stayed for a few million years and left/gone extinct and we'd never know about it except possibly as a footnote about some weird isotopic mixes in a particular igneous rock.

[Mechalich]

An industrial civilization would be noticed. It would leave behind a depositional layer with anomalous spectroscopy if nothing else. Even a pre-industrial metal-using civilization would leave clear traces - for instance if you were looking at a deposition representing thousands of years of Roman-era development you'd wonder what was with all the lead.

A society that never developed metalworking would be much more difficult to detect, but it is important to remember that a hypothetical Mesozoic Stone Age would likely have persisted for millions of years just as ancestral hominin species did, so there would be more time to accumulate evidence in the fossil record. If we talking about some kind of dromeosaur that ran around the late Cretaceous for a few million years with hand axes - yes we have now sufficiently investigated those strata that it would be hard to miss.

By contrast, if you're talking about advanced aliens briefly visiting the Earth at some point in deep time, even for thousands of years, that would indeed be extremely difficult to detect.

[Knaight]

Of course, the whole bit about the "meteor killed the dinosaurs" theory is that there is tiny sliver of weird (presumably from the asteroid) elements exactly at the K-T boundary. So if a civilization rose up and destroyed itself, all the pollution should be found in that boundary. I wonder what type of process fills the atmosphere with iridium (the oddball element in the K-T layer which is presumably leftover meteor).

There's also a massive crater with those same elements in extra high abundance that can be dated to the same time, and that little detail is what really clinched that as the dominant theory. A civilization rising up and destroying itself would look different for that reason as well.

[Rockphed]

There's also a massive crater with those same elements in extra high abundance that can be dated to the same time, and that little detail is what really clinched that as the dominant theory. A civilization rising up and destroying itself would look different for that reason as well.

Ah, but what if the Dinosaurs crashed a rock in to the planet in some misguided attempt to win a war?:smallcool:

[factotum]

Ah, but what if the Dinosaurs crashed a rock in to the planet in some misguided attempt to win a war?:smallcool:

Realise you're not serious, but if they were advanced enough to do that then we're talking a civilization with space travel capability, and things in space tend to last a *lot* longer than stuff on the ground--something placed in a geostationary orbit 60 million years ago would probably still be up there!

[snowblizz]

The was a pretty interesting article about that very subject a few week ago on The Atlantic. The gist of it as far as I could figure it out is that post industrial revolution our sediment layers will be very weird (lots of nitrogen, odd carbon isotopes, rare earths showing up all over the place, etc..) and that might be a clue but a society that never got to that point would be all but impossible to detect.


https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/
Funnily enough I saw the thread title and was gonna go find that article. It's rather interesting,




I'd be very surprised if we hadn't noticed something by now. Besides material evidence (ie tools, clothing, etc.), there's tons of other things we ought to have seen by now. Injury patterns on bones indicating that they were struck by tools, not teeth or claws. Old, severe injuries that were healed, indicative of a support structure for wounded members of their society. Fire pits. Shaped stone or wood. Collections of beads. Mixing of dissimilar species (think sheep and shepherd).

My vote: If there had been a sentient species that behaved anything like humans did, we probably would have found it by now. That being said, we have only found a finger bone and 3 teeth from one of our nearest cousins, the Denisovans, who disappeared a mere 30k-50k years ago.
The timespan we are talking about here are geological though not archeological. To take some of what the article discussed how do you find traces when the continental plate the civilization lived on has subducted into the earth's core, stuff like that.



The things you're talking about as being things that we ought to have found are all things that I'm pretty sure wouldn't last 60 million years, as they'd have to in this case. The one area where I agree with you is stuff that's preserved in the bones, so we'd have found them in fossils--signs of bones repaired using medical techniques, bone injuries caused by weapons, and of course a skull cavity big enough to contain a brain capable of human-like levels of reasoning, all ought to have been discovered by now if they were there to find.
Should be pointed out that fossiles only cover stuff that happened to be abundant enough* to live in places where fossilization was feasible. We keep forgetting that the picture of what we think prehistoric life was like is founded on an extremely narrow set of fossiles. Just as today we estimate we only know a fraction of the species (though the most "major" ones we probably got) similarly there can be entire evolutionary lines we have no record of. Basically it's difficult to say how broadly the fossile records cover extinct species.

*and it's not even proof of that, conceivably every fossile found of T-Rexes may represent the entirety of the species, it would be ludicrously improbable but yet it could be.

[wumpus]

Ah, but what if the Dinosaurs crashed a rock in to the planet in some misguided attempt to win a war?:smallcool:

Possible (I'm fairly sure both sides built cobalt bombs during the cold war), but there's also the possibility that a facility to mine an asteroid was left in Earth orbit. Long the dino civilization collapsed, the asteroid fell down on the planet.


Realise you're not serious, but if they were advanced enough to do that then we're talking a civilization with space travel capability, and things in space tend to last a *lot* longer than stuff on the ground--something placed in a geostationary orbit 60 million years ago would probably still be up there!

I really have to question this. While the Earth's atmosphere might take more than 60 million years to pull satellites in geosync down, that isn't their only fate. Geosync satellite need some sort of propulsion system on board, simply to stay in place. The biggest reason they need those motors is the Moon: it keeps pulling them more and more toward itself (and always pulls just a little bit harder away from Earth than toward it). And once a satellite is pulled a little beyond geosync, it will gradually slide eastward from it's former stationary position (until the motors fire and push it back). I'd expect the Moon to eventually kick a formerly geosync satellite into an eccentric orbit that would interfere with the atmosphere, get ejected into the solar system (into a more or less heliocentric orbit that might eventually re-collide with Earth over millions of years), or collide with the Moon (without an atmosphere, near misses don't count but make a huge difference in the orbit).

An orbit that looks stable for decades or hundreds of years (Vanguard 1, the second US satellite is expected to return to Earth 400 years from now) isn't necessarily stable over millions of years (Lagrange points L4 and L5 are another story).

I'd also be curious how much the lunar surface was pummeled by meteors over 60 million years, and how deep the fallen debris might be on top of any dinosaur artifacts left there (I'd assume that Mars dust storms would eliminate just about anything over 60 million years, regardless how wimpy we might see them (the thing in The Martian was a fake way to set up the rest of the book).

[factotum]

I really have to question this. While the Earth's atmosphere might take more than 60 million years to pull satellites in geosync down, that isn't their only fate. Geosync satellite need some sort of propulsion system on board, simply to stay in place. The biggest reason they need those motors is the Moon: it keeps pulling them more and more toward itself (and always pulls just a little bit harder away from Earth than toward it).

The relevant section of the Wikipedia article suggests that the effect you're talking about is a cyclic one with a period of 53 years (e.g. the orbit will return to its original one after that time period), and apparently there are also two "stable" points in the geostationary orbit that satellites tend to migrate towards:

https://en.wikipedia.org/wiki/Geostationary_orbit#Orbital_stability

Geostationary satellites need thrusters to counteract these two effects and stay on their assigned station. I don't think it would be possible for the Moon to give the sort of kick you're talking about unless an object got very close to it.

[wumpus]

The relevant section of the Wikipedia article suggests that the effect you're talking about is a cyclic one with a period of 53 years (e.g. the orbit will return to its original one after that time period), and apparently there are also two "stable" points in the geostationary orbit that satellites tend to migrate towards:

https://en.wikipedia.org/wiki/Geostationary_orbit#Orbital_stability

Geostationary satellites need thrusters to counteract these two effects and stay on their assigned station. I don't think it would be possible for the Moon to give the sort of kick you're talking about unless an object got very close to it.

Stable for decades and stable for 60 million years are two different things. Here's a paper on long term stability in the ex-geosync "graveyard orbit":
https://conference.sdo.esoc.esa.int/proceedings/sdc7/paper/864/SDC7-paper864.pdf

While it doesn't see ejection as much of a possibility, it does see Earth reentry as quite possible within 120 years. Since the graveyard orbit is strictly further out than geosync, I'd expect similar effects on all Earth-orbiting satellites over tens of millions of years. The important issue is that the Moon is batting these things around in a chaotic system, not the steady pressure of the air in low Earth orbit (so oddball effects like ejection or lunar collision are quite possible).

I wonder how many satellites would have to be launched (and presumably be stuffed in the graveyard orbit) for any to survive? Probably more than we've launched, but we haven't fooled around with leaving planet smashing asteroids in potential Earth colliding orbits.

[Rockphed]

Stable for decades and stable for 60 million years are two different things. Here's a paper on long term stability in the ex-geosync "graveyard orbit":
https://conference.sdo.esoc.esa.int/proceedings/sdc7/paper/864/SDC7-paper864.pdf

While it doesn't see ejection as much of a possibility, it does see Earth reentry as quite possible within 120 years. Since the graveyard orbit is strictly further out than geosync, I'd expect similar effects on all Earth-orbiting satellites over tens of millions of years. The important issue is that the Moon is batting these things around in a chaotic system, not the steady pressure of the air in low Earth orbit (so oddball effects like ejection or lunar collision are quite possible).

I wonder how many satellites would have to be launched (and presumably be stuffed in the graveyard orbit) for any to survive? Probably more than we've launched, but we haven't fooled around with leaving planet smashing asteroids in potential Earth colliding orbits.

Civilization ending meteoric events happen with incredible regularity, right? Maybe that regularity is the time it takes for a civilization to arise and develop hubris enough to think that parking a giant rock in an unstable orbit is a good idea!

[AMX]

What about resource depletion?
We're digging out coal seams that predate the mesozoic, wouldn't we notice if somebody else had mined out a bunch of them already?

[Grey_Wolf_c]

What about resource depletion?
We're digging out coal seams that predate the mesozoic, wouldn't we notice if somebody else had mined out a bunch of them already?

Depending on how long coal takes to form, would we even be competing for the same seams? Or would our seams still be partially formed coal back in their time?

Also, any civ that's progressed to mass-digging coal might not leave partially-consumed seams behind that we'd "finish off" - they'd exploit them to the point they're not worth digging anymore, so we'd never even start them.

On the other hand, the fact that there is so much fossil fuels left might indicate there never was a fossil fuel-powered civ before us.

GW

[Rockphed]

What about resource depletion?
We're digging out coal seams that predate the mesozoic, wouldn't we notice if somebody else had mined out a bunch of them already?

*Dons tin-foil hat* Well, maybe that is why there is no coal from the Permian-Triassic boundary. Dinosaurs 66 million years ago used it all up to power their civilization.

edit:

Depending on how long coal takes to form, would we even be competing for the same seams? Or would our seams still be partially formed coal back in their time?

Also, any civ that's progressed to mass-digging coal might not leave partially-consumed seams behind that we'd "finish off" - they'd exploit them to the point they're not worth digging anymore, so we'd never even start them.

On the other hand, the fact that there is so much fossil fuels left might indicate there never was a fossil fuel-powered civ before us.

GW

Coal only takes a couple million years to form. We exploit coal that goes back pretty much all the way back to when life first formed on earth.

[Knaight]

Civilization ending meteoric events happen with incredible regularity, right? Maybe that regularity is the time it takes for a civilization to arise and develop hubris enough to think that parking a giant rock in an unstable orbit is a good idea!

Not really - most mass extinctions don't tie to meteoric events. You get the occasional huge volcano, but then there's things like drastic changes in atmosphere composition because of novel species which are if anything more common.

[Rockphed]

Not really - most mass extinctions don't tie to meteoric events. You get the occasional huge volcano, but then there's things like drastic changes in atmosphere composition because of novel species which are if anything more common.

As far as I can tell, the only mass extinction that ties to a meteor is the Chicxulub event about 66 million years ago. There are some people who think the Permian-Triassic boundary is an impact event, but it isn't proven (partially because we cannot find a crater).

[wumpus]

Civilization ending meteoric events happen with incredible regularity, right? Maybe that regularity is the time it takes for a civilization to arise and develop hubris enough to think that parking a giant rock in an unstable orbit is a good idea!

In the case of a giant rock parked in a decaying orbit, in all likelyhood the civilization collapsed first, then a few decades/centuries later the big rock came down and wiped out most life. Even then, it took plenty of years for the dinosaurs to die out. Assuming there are known post-meteor fossils, that implies plenty long time (I'm pretty sure the K-T boundary compresses a lot of time into a tiny layer).

I'd be curious about age of fossil fuels and their distribution. While we can be reasonably sure no "Altantean" civilization was capable of fossil fuel use (nor widespread metal use), more fuel would certainly have been laid down after the dinosaurs.

[Vinyadan]

I wonder how much of a domino effect there can be with extinction, and if there is a "critical mass" that can trigger mass extinction. After all, the species are all connected. So the death of bees can cause problems for flower plants, which leads to problems for herbivores, which is bad for carnivores. Or I think of the little denizens I almost never hear about, like bacteria producing B12 vitamin. What would happen, if, for example, a virus strain were to develop that specifically targets these bacteria?

[Rockphed]

I wonder how much of a domino effect there can be with extinction, and if there is a "critical mass" that can trigger mass extinction. After all, the species are all connected. So the death of bees can cause problems for flower plants, which leads to problems for herbivores, which is bad for carnivores. Or I think of the little denizens I almost never hear about, like bacteria producing B12 vitamin. What would happen, if, for example, a virus strain were to develop that specifically targets these bacteria?

In general, extinctions have not affected insects nearly as much as they have impacted vertebrates.

[AMX]

I'd be curious about age of fossil fuels and their distribution. While we can be reasonably sure no "Altantean" civilization was capable of fossil fuel use (nor widespread metal use), more fuel would certainly have been laid down after the dinosaurs.

That's actually why I specifically mentioned coal - there's a reason why the Carboniferous period has that name :smallwink:

[Tvtyrant]

I think sentient/sapient life is probably more common then we think, but civilization is unlikely to happen twice.

1. The Halocene climate is one of the rare times the planet has not been in a deep ice age or extremely hot and arid.

2. In the world there are only 4 places agriculture developed independently. Of those, only New Guinea is not based on the seeds of flowering plants.

3. All domesticated draft animals are hooved, not all hooved animals are domesticatable and hooves are relatively new.

4. The bodyparts needed to maximize brain utility are unrelated to intelligence. Dextrous appendages for manipulation, the ability to throw held objects, decent vision, etc. A sentient dog is never going to be able to build walls, complex tools or likely even fires.

A sentient dinosaur lacks the ability to utilize ranged weapons, flowering crops for agriculture, and likely lived in a resource barren world. Seeing that many groups leave little trace due to resource barrenness despite being humans with every other advantage, it seems unlikely we would ever know.

[Lvl 2 Expert]

*Dons tin-foil hat* Well, maybe that is why there is no coal from the Permian-Triassic boundary. Dinosaurs 66 million years ago used it all up to power their civilization.

Maybe a late Permian civilization ran on peat and brown coal and such (and seafloor algae deposits, details, details), preventing the transformation of these resources into coal and oil.



We modern people changed the world a lot, but also over a really short period. If we disappeared tomorrow much of our changes would ultimately have been around for maybe a few hundred years. That's pretty short. Changes we made during say the late stone age on the other hand have been around for thousands or tens of thousands of years. Changes to the atmosphere due to deforestation, starting a trend lasting to today. And stone age people have another advantage: stone preserves pretty well. Stonehenge, dolmens, pyramids and those Easter Island statues might still be retrievable in some recognizable shape several millions of years from now. Maybe some stone carved early writing would even survive. And because of how spread out over time these things are they have a decent chance of at least some of them escaping even if something big does happen that cab damage them significantly. Even earlier you're not looking for a civilization, but for a species. You want to find something with a large enough brain to be a candidate. If our own track record is an indication those fossils should be there over a span of hundreds of thousands of years. Although I guess if they were say a species of bird, fast evolving with small bones that don't preserve as well as larger ones, we could even miss that.

Overall though, maybe it's the signs of early civilization we would expect to find, rather than anything pointing out the height of their power.

[Rockphed]

Maybe a late Permian civilization ran on peat and brown coal and such (and seafloor algae deposits, details, details), preventing the transformation of these resources into coal and oil.

Also, the atmospheric concentration of CO2 rose by about 2000 ppm and 95% of all species died out. Anthropogenic* global warming induced disaster confirmed!

*Or Therapsidpogenic or whatever as the case may be.

[Solaris]

3. All domesticated draft animals are hooved, not all hooved animals are domesticatable and hooves are relatively new.

The rest of your points are good ones, but this one's rather weak. There were dinosaurs that lived in herds.
I like "Dinosaurs had small, simple brains compared to mammals" better. Even the cleverest dinosaurs were likely dimmer than wolves, judging by their brains.

[Mechalich]

I think sentient/sapient life is probably more common then we think, but civilization is unlikely to happen twice.

1. The Halocene climate is one of the rare times the planet has not been in a deep ice age or extremely hot and arid.

2. In the world there are only 4 places agriculture developed independently. Of those, only New Guinea is not based on the seeds of flowering plants.

3. All domesticated draft animals are hooved, not all hooved animals are domesticatable and hooves are relatively new.

4. The bodyparts needed to maximize brain utility are unrelated to intelligence. Dextrous appendages for manipulation, the ability to throw held objects, decent vision, etc. A sentient dog is never going to be able to build walls, complex tools or likely even fires.

A sentient dinosaur lacks the ability to utilize ranged weapons, flowering crops for agriculture, and likely lived in a resource barren world. Seeing that many groups leave little trace due to resource barrenness despite being humans with every other advantage, it seems unlikely we would ever know.

Dinosaurs coexisted with flowering plants for essentially the entirety of the Cretaceous, and they were well on their way to their current dominance compared to conifers. It is grasses that did not evolve until relatively recently, emerging only in the past 40 million years or so that we rely upon for crops.

While it is true that all domestic draft animals are members of the ungulate clade (with the exception of elephants if you consider them domesticated), this is largely a function of essentially all large, non-predatory terrestrial animals on the planet being members of the ungulate clade at present - the exceptions are elephants and our fellow great apes. Outside of that you're down to capybaras and the like. There's nothing special about hooves as a structure for producing draft animals.

[Lleban]

The rest of your points are good ones, but this one's rather weak. There were dinosaurs that lived in herds.
I like "Dinosaurs had small, simple brains compared to mammals" better. Even the cleverest dinosaurs were likely dimmer than wolves, judging by their brains.

Just gonna throw this out but the way we measure intelligence in mammals doesn't really apply well to Archosaurs.(crocodiles, dinos,pterosaurs and birds) We don't really have an accurate idea of the intelligence of dinosaurs but we don't have much reason to doubt that say a hadrosaur would be less intelligent than a cow living in a similar niche.

[Lvl 2 Expert]

Also, the atmospheric concentration of CO2 rose by about 2000 ppm and 95% of all species died out. Anthropogenic* global warming induced disaster confirmed!

*Or Therapsidpogenic or whatever as the case may be.

Wait. Oil mostly forms from algae and plankton remains on the sea floor. Also, the extinction event was worse in the sea (90-95% of all species) than on land (~70%). We might be looking at a marine civilization.

Which makes sense. End Permian we're talking a bit over 250 million years ago. On land all the brainiest animals are amniota, whose base features were established maybe 320 million years ago. The basic cephalopod design dates back from at least about 450 million years. And that's just based on the shells. By 320 mya there were full fledged octopuses swimming around. (Well, sort of.) Modern day octopi show some real smarts (https://www.youtube.com/watch?v=JOV-DlxTiFU), like this captive giant octopus (https://youtu.be/Q36_8s5z6S8?t=1m27s) figuring out sharks can't breath if they stop swimming, and deploying that knowledge against them.

Octopuses have good senses to help make sense of their environment, and plenty of arms to manipulate it with. An underwater civilization would furthermore not leave a lot of evidence after all that time, as sea water takes both a mechanical and a chemical toll on anything sitting in it. Without regular upkeep the Eiffel tower would have been rusty today, but it would still stand. A ship from the same period would have rusted through and sunk, and started breaking apart. The Titanic is not much of a looker these days, is what I'm saying. Even the great pyramids, the Hoover dam or Mount Rushmore wouldn't last anywhere near 250 million years in an undersea environment. Just bits and pieces. And that's without taking into account the fact that because of plate tectonics and the supercontinent cycle the very oldest seafloor/oceanic crust is around 280 million years old, and outside of the Mediterranean the oldest bits are even as young as 200 million years. So the parts of the earth where traces could still exist today at all are tiny.

250 mya is just when supercontinent Pangea is slowly starting to develop cracks. That could have been a great time for any sea life able to use the newly forming environments and the resources that became available because of it. Marine reptiles were pretty much absent at this time but suddenly boomed as the Triassic started and sharks mostly lived in freshwater.

I'm not even really sure how I would go about disproving this hypothesis. Octopuses have some form of a residual internal shell, but it's not in any way a skull like feature, as evidenced by the fact that they can squeeze themselves through openings not much bigger than their eyes (or their beak, probably depending on species). So we really don't have much of a way to even look at brain sizes for extinct octopi (or squid, or nautiloids), in contrast with dinosaurs. On top of that much of their nervous system seems to be decentralized, with octopus arms housing a suspiciously large amount of neurons. So even a small central brain would not prove much.


This might be one of my favorite "yeah I don't really have any direct evidence, but you can't disprove it either" theories now.

[hamishspence]

Just gonna throw this out but the way we measure intelligence in mammals doesn't really apply well to Archosaurs.(crocodiles, dinos,pterosaurs and birds) We don't really have an accurate idea of the intelligence of dinosaurs but we don't have much reason to doubt that say a hadrosaur would be less intelligent than a cow living in a similar niche.

Maybe they should be thought of as super-sized versions of birds in that niche - geese and the like.

Thinking of a hadrosaur as a "scaled-up goose" might be more useful than thinking of it as a reptilian cow.

[Tvtyrant]

The rest of your points are good ones, but this one's rather weak. There were dinosaurs that lived in herds.
I like "Dinosaurs had small, simple brains compared to mammals" better. Even the cleverest dinosaurs were likely dimmer than wolves, judging by their brains.

Being a herd animal does not render one domesticatable or good at draft pulling. Llamas are domesticatable and can't be used for plowing or pulling heavy loads, zebras, rhinos, hippos and giraffes can pull loads and are not domesticatable.

I don't know how useful that is though. Cephalopoda could easily produce an intelligent, self-aware creature that couldn't make much use of tools or agriculture. My main argument is that it takes a laundry list of traits for civilization to occur, and these are unlikely to occur together. Dolphins being the modern example.

[Vinyadan]

Wait. Oil mostly forms from algae and plankton remains on the sea floor. Also, the extinction event was worse in the sea (90-95% of all species) than on land (~70%). We might be looking at a marine civilization.

Which makes sense. End Permian we're talking a bit over 250 million years ago. On land all the brainiest animals are amniota, whose base features were established maybe 320 million years ago. The basic cephalopod design dates back from at least about 450 million years. And that's just based on the shells. By 320 mya there were full fledged octopuses swimming around. (Well, sort of.) Modern day octopi show some real smarts (https://www.youtube.com/watch?v=JOV-DlxTiFU), like this captive giant octopus (https://youtu.be/Q36_8s5z6S8?t=1m27s) figuring out sharks can't breath if they stop swimming, and deploying that knowledge against them.

Octopuses have good senses to help make sense of their environment, and plenty of arms to manipulate it with. An underwater civilization would furthermore not leave a lot of evidence after all that time, as sea water takes both a mechanical and a chemical toll on anything sitting in it. Without regular upkeep the Eiffel tower would have been rusty today, but it would still stand. A ship from the same period would have rusted through and sunk, and started breaking apart. The Titanic is not much of a looker these days, is what I'm saying. Even the great pyramids, the Hoover dam or Mount Rushmore wouldn't last anywhere near 250 million years in an undersea environment. Just bits and pieces. And that's without taking into account the fact that because of plate tectonics and the supercontinent cycle the very oldest seafloor/oceanic crust is around 280 million years old, and outside of the Mediterranean the oldest bits are even as young as 200 million years. So the parts of the earth where traces could still exist today at all are tiny.

250 mya is just when supercontinent Pangea is slowly starting to develop cracks. That could have been a great time for any sea life able to use the newly forming environments and the resources that became available because of it. Marine reptiles were pretty much absent at this time but suddenly boomed as the Triassic started and sharks mostly lived in freshwater.

I'm not even really sure how I would go about disproving this hypothesis. Octopuses have some form of a residual internal shell, but it's not in any way a skull like feature, as evidenced by the fact that they can squeeze themselves through openings not much bigger than their eyes (or their beak, probably depending on species). So we really don't have much of a way to even look at brain sizes for extinct octopi (or squid, or nautiloids), in contrast with dinosaurs. On top of that much of their nervous system seems to be decentralized, with octopus arms housing a suspiciously large amount of neurons. So even a small central brain would not prove much.


This might be one of my favorite "yeah I don't really have any direct evidence, but you can't disprove it either" theories now.

Oh look, it was Cthulhu all along.

About draft animals underwater:

https://youtu.be/CA-eyG7lUv8?t=18s

[wumpus]

This might be one of my favorite "yeah I don't really have any direct evidence, but you can't disprove it either" theories now.

While I've been harping on a dino-caused Chicxulub event, I'd assume that 60 millions years from now the only trace of the anthrocene layer would be a mass extinction of nearly all land animals (land and sea).

I'd be curious if you could show that all "large marine survivors" of any mass extinction (preferably otherwise unexplained) could be all reasonably useful once domesticated (the "surviving" species would nearly all be post-domestication).

Plug for "tierzoo": zoology analyzed as if species were builds in some sort of MMO/RPG: https://www.youtube.com/channel/UCHsRtomD4twRf5WVHHk-cMw
(domestic cats and dogs are placed on the "God tier" thanks to support from humans).

[Bucky]

Humans are leaving a bunch of other durable traces, namely:
* Disturbance of rock layers over a billion years old, selectively removing certain minerals
* Drilling very deep, straight vertical shafts and then plugging or backfilling them with foreign material
* Depleting uranium; depleted uranium will remain detectably tampered-with for billions of years
* I expect nuclear waste to be disposed of in a way that keeps its packaging intact for hundreds of millions of years
* Splicing genes from some organisms into unrelated organisms; this will remain detectable to future molecular phylogeneticists as long as those organisms' descendants survive
* Very local, relatively thick rock strata composed of concrete and oxidized steel; these won't survive everywhere, but in some places they will be protected from erosion and defy geological explanations
* Artifacts left on the moon will likely remain for tens of millions of years, though they will experience weathering

Of those, to my knowledge we've found three - disturbed very old rock formations, and depleted uranium mixed with nuclear waste. We aren't thorough enough to rule out gene splices. I don't think we've come across artificial minerals, deep boreholes or lunar artifacts.

[Grey_Wolf_c]

Of those, to my knowledge we've found three - disturbed very old rock formations, and depleted uranium mixed with nuclear waste.

[citation needed]

GW

[Kato]

[citation needed]

GW

This... Also, I feel like concrete leftover would be pretty obvious to a geologist. Especially if we talk about building / city worth of it. There might be some randomness to it but if you have a large urban area you will either find a lot or nothing, it seems to me.

And relics of genetic tampering? How would you check for this a hundred million years/ a million generations later? :smallconfused:

[Yora]

From personal experience, we can identify dirt floors in ancient structures because the soil levels are completely different in how they look and function. A floor has been deliberately packed down and is quite dense, while any debris that settled on top of it is loose and easy to move. I'd imagine this would show up in the fossil record as well if it were there.

And then there's holes. Holes can be filled in, but in most cases you never get the same homogenous structure that was placed down when the ground formed through geologic processes. If we are talking about civilization, even neolithic ones, we would see some celars, irrigation ditches, quarries, or mines.

[King of Nowhere]

As many have pointed out, an industrial civilization would leave traces all over the place. A preindustrial civilization would leave smaller traces, and it is not impossible that those would not be detected. So, we could not really rule out that there was a civilization, but it collapsed before it reached industrial technology, right?

Except... how would it collapse?

An industrial civilization has lots of ways to destroy itself, something we started to recognize and counteract in recent decades. But a preindustrial civilization can't, not really. Sure, a local civilization can collapse because the wheater pattern changed, but civilization in another area will flourish for the same reason. A war, famine or plague may be devastating, but in a few generations civilization will have recovered; it's what happened, many times, hystorically.
Basically, when a creature becomes advanced enough to figure out fire and clothes (not to mention basic weapons and group tactics to deter predators), it will spread out from its original niche (the one where the climate was right for it) to all over the world. We humans went out of africa and spread everywhere in some 30-40 thousand years, before we even formed anything we could call civilization. And then there is really no catastrophe that is global enough to wipe out everyone, not unless you look at meteor impacts much bigger than the dinosaur extinction - ssomething that can destroy all multicellular life, or at least all life bigger than cocroaches. and given a steady, large environment (discounting thus cases like easter island), inventions will accrue, slowly but steadily. The process get faster when people inventi writing, then the alphabet, then printing.

So, if a primitive civilization does develop, it will eventually inevitably progress to an industrial one. and then we'd see its traces all over the place. Notice that when a civilization is born, the race that created it has already covered every livable bit of the planet, and there's every chance it will create civilization elsewhere with enough time.

No, we cannot completely rule out a mesozoic civilization that collapsed before going industrial. We cannot, however, see any way in which such civilization could collapse before going industrial.


Wait. Oil mostly forms from algae and plankton remains on the sea floor. Also, the extinction event was worse in the sea (90-95% of all species) than on land (~70%). We might be looking at a marine civilization.



A marine civilization however would be severely limited. It could not use fire.

[Andor13]

I'm pretty sure the dinosaur impact would have killed pre-industrial us. Not only did the nuclear winter last centuries, not only did almost all food sources die, but IIRC the geologic evidence shows global oxygen levels crashed too low to sustain a mammal of our size for decades. Hell, I'm not sure current us could survive the chixalub impact for longer than a few years.

As for wiping out a pre-industrial civilization, without a global catastrophe, we don't know enough. It seems unlikely we (as a species, not as an individual civilization, those collapse all the time) could have been wiped out by a non-global extinction event but we are an evolved generalist, and we have no way of knowing how common a trait that may be for intelligent species. An intelligent specialist species would be vulnerable to the loss of whatever they specialize in.

[King of Nowhere]

I'd definitely think we'd survive the extinction. Humans are very adaptable, which is what let us spread from the tropics to the arctic.


Omnivores, insectivores, and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources


All major Cretaceous mammalian lineages survived the K–Pg extinction event, although they suffered losses

I didn't find the drop in oxygen, but there are people living in tibet, and I don't see any mechanism that would have dropped oxygen below that level. The main causes of extinction were

- dust in the atmosphere preventing photosynthesis, causing massive plant dieoff. this killed the herbivorous, which killed the carnivorous. those that fed off carrion were fine. Humans can feed off carrion, or off carrion-eaters. insects and invertebrates were an important protein source before we learned to hunt bigger animals.

- dust in the atmosphere cause a global cooling, which killed off those species that could not adapt to cold; afterwards, there was a quick heating, which killed off a lot of what remained, which was more cold tolerant than heat tolerant. Humans can just put on a coat and then put it off.

- Acidic rain was bad for plants. Humans' layer of skin fat is fairly effective against acid, provided it's not too concentrated. Plus, we can fashion umbrella.

And while we may not know if another sapient species would be a generalist, the thing is that intelligence make a species generalist. A carnivorous species may learn to breed carrion-eaters. An herbivorous species would probably be screwed, although they may learn to find seeds - or maybe they could eat fungi, lichens, or the few vegetables that would manage to survive in the little light that passed - some species adapted to penumbra may well find enough light to thrive, and we'de be better equipped to compete for those. A cold-blooded species can use clothes and adapt to a wide range of temperatures.

But let's even assume that none of what said above applies, and that the dinosaur impact would have managed to kill even a sapient species. We humans managed to go from agriculture to industry in 10000 years. Say another species would take much longer, 100000 years. that's ery little time geologically. they'd need to have evolved less than 100000 years the impact, which is very unlikely. the dinosaurs have existed for 200 million years, and they evolved a sapient species exactly in the last 1/2000th of that time, before being wiped out by something totally unrelated? quite a coincidence it would be.
All things considered, I maintain that a dinosaur civilization arising in the very end of the cretaceous and then being wiped out by the asteroid without reaching industrialization would require a helluva lot of unlikely coincidences

[Mechalich]

A pre-industrial sapient species could go extinct as a result of a sufficient catastrophe. There is evidence that this almost happened to modern humans via the Toba Catastrophe Hypothesis (https://en.wikipedia.org/wiki/Toba_catastrophe_theory).

However, it is very likely that any non-industrial sapient species would persist for a considerable period of time. The average mammal species persists for around one million years, which is a lot of time to accumulate paleontological evidence - which is why Africa is full of stone tools made by various hominin ancestor species. Fossil rarity increases as you go further back into deep time, but if there had been a persistent tool-using species during the Mesozoic there would be a good chance of finding evidence eventually.

[factotum]

I didn't find the drop in oxygen, but there are people living in tibet, and I don't see any mechanism that would have dropped oxygen below that level. The main causes of extinction were

- dust in the atmosphere preventing photosynthesis, causing massive plant dieoff.

Um, isn't this the mechanism you were looking for? Green plants maintain the oxygen levels in our atmosphere, a massive die-off of them would likely also cause a reduction in atmospheric oxygen given enough time. Not sure what Tibet has to do with it, because atmospheric circulation means that places that don't have plants can get oxygen from the places that do--in fact, something like 20% of the entire world's oxygen comes from the Amazon rainforest.

[Bucky]

[citation needed]

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
https://en.wikipedia.org/wiki/Volcanic_pipe

[Bohandas]

Ia Ia Cthulhu Fhtagn

[Kato]

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
https://en.wikipedia.org/wiki/Volcanic_pipe
Except neither is quite what you claimed... One is just a uranium site dense enough to start nuclear chain reactions (barely) and nothing indicates it must or even should be a waste site, and the other is basically a special kind of volcanoe. Are all volcanoe proof of a mining civilization?



So, if a primitive civilization does develop, it will eventually inevitably progress to an industrial one. and then we'd see its traces all over the place. Notice that when a civilization is born, the race that created it has already covered every livable bit of the planet, and there's every chance it will create civilization elsewhere with enough time.

No, we cannot completely rule out a mesozoic civilization that collapsed before going industrial. We cannot, however, see any way in which such civilization could collapse before going industrial.

Eh... I don't want in general disagree with your opinion but your extrapolating all of your assumptions from one data point. Because you/we can't think of a way for a civilization to go extinct, it doesn't mean it can't happen. I'm very willing to agree, even having a basic civ is useful in surviving but I'm not convinced it will guarantee there's not something that can kill you.
In the same vein, because it is true for us doesn't mean another species must have covered the planet before developing a civ, nor does it mean advancing beyond a basic civilization is inevitable. Heck, we do have evidence for that, looking at all the civs around the world that did not keep up with Eurasian ones and thus where at a severe disadvantage whn they collided. No, we cannot guarantee they couldn't have caught up, but it's also possible they were stuck for some reason or other.

[King of Nowhere]

A pre-industrial sapient species could go extinct as a result of a sufficient catastrophe. There is evidence that this almost happened to modern humans via the Toba Catastrophe Hypothesis (https://en.wikipedia.org/wiki/Toba_catastrophe_theory).

That goes towards proving my point:
1) humans still lived only in africa at the time. they had no civilization, they were smart tool users but still just that.
2) despite massive dieoff, humankind managed to survive.
My point for the difficulty of extinction of a sapient species is that it will spread out (which at the time of the toba event hadn't happened yet) and then somebody, somewhere, will survive. Somewhere, local conditions will be less hellish than elsewhere, or someone will find the right way to cope.

And do note that the toba catastrophe is still a debated hypothesis.


Um, isn't this the mechanism you were looking for? Green plants maintain the oxygen levels in our atmosphere, a massive die-off of them would likely also cause a reduction in atmospheric oxygen given enough time.

Our atmmosphere has enough oxygen that we could still breath for a few millennia even if all photosynthesis suddenly stopped. Considering that most animals - oxygen consumers - also died, then the drop in oxygen level wasn't severe, or even significant enough to be felt.



Not sure what Tibet has to do with it

People living in Tibet have a much lower amount of oxygen to breath, because atmosphere is less dense with altitude. They adapted to live in a low-oxygen environment, and they do just fine. THere are two more populations living in high plateaus, and they all independently developed adaptations.

Now, rise of carbon dioxide would be a greater concern. Carbon dioxide is in much lower amount than oxygen, so its relative concentration will rise much more quickly (and the rise of carbon dioxide was responsible for the following heating up). It is lethal in concentration around 5% in air, even if there is enough oxygen. However, taking into account the projected lenght of the nuclear winter, and the fact that many forests burned, releasing carbon dioxide, it is unlikely its level reached 1% of the atmosphere. And 1% carbon dioxide make most people feel drowsy, and it may cause some illnesses over prolonged exposure, but it is generally non fatal, even for prolonged exposure.

All things considered, photosynthesis did NOT stop for long enough to make the air unbreathable.



Eh... I don't want in general disagree with your opinion but your extrapolating all of your assumptions from one data point. Because you/we can't think of a way for a civilization to go extinct, it doesn't mean it can't happen. I'm very willing to agree, even having a basic civ is useful in surviving but I'm not convinced it will guarantee there's not something that can kill you.



True. In fact I am not presenting those arguments as scientifical certainties. They are, however, reasonable hypothesis. And I am not saying it is impossible that a sapient, tool-using, preindustrial species would go extinct for natural causes; merely very, very unlikely.


In the same vein, because it is true for us doesn't mean another species must have covered the planet before developing a civ, nor does it mean advancing beyond a basic civilization is inevitable. Heck, we do have evidence for that, looking at all the civs around the world that did not keep up with Eurasian ones and thus where at a severe disadvantage when they collided. No, we cannot guarantee they couldn't have caught up, but it's also possible they were stuck for some reason or other.

Spreading out through all the planet happens spontaneously over long time scales. You are fighting for resources with the other tribe, but if you move 30 km away there will be no one to compete with you. So you move. The next generation will move again. If there are no climatic barriers to stop you (the sahara desert kept humankind bottled up for most of our hystory, but we eventually overcame it; and a sapient species is very good at dealing with climatic barriers anyway), you will eventually cover the whole world.
And while many societies may stagnate, the fact is that somewhere in the world, someone will progress. And then innovation will spread. Which is what happened when eurasian civilizations met the other ones, whether it happens peacefully or by conquest. It doesn't need all civilizations to develop, or even most of them.

[Andor13]

Our atmmosphere has enough oxygen that we could still breath for a few millennia even if all photosynthesis suddenly stopped. Considering that most animals - oxygen consumers - also died, then the drop in oxygen level wasn't severe, or even significant enough to be felt.

People living in Tibet have a much lower amount of oxygen to breath, because atmosphere is less dense with altitude. They adapted to live in a low-oxygen environment, and they do just fine. THere are two more populations living in high plateaus, and they all independently developed adaptations.

As you note, the KT impact event also caused world wide fires, which would consume a good chunk of the oxygen, and it would not be quickly replenished due to the dust shroud.

Also high altitude adaptations, or even the capacity for them, would not help in a quick crash scenario, unless the high-altitude dwellers understood oxygen concentrations, and had a zip-line to the sea shore.

Ah, I found a paper (https://www.thenakedscientists.com/forum/index.php?topic=39488.0) arguing for the Oxygen Crash scenario, although I don't think it's where I got the idea from, that was years ago.

[King of Nowhere]

As you note, the KT impact event also caused world wide fires, which would consume a good chunk of the oxygen, and it would not be quickly replenished due to the dust shroud.

Also high altitude adaptations, or even the capacity for them, would not help in a quick crash scenario, unless the high-altitude dwellers understood oxygen concentrations, and had a zip-line to the sea shore.

Ah, I found a paper (https://www.thenakedscientists.com/forum/index.php?topic=39488.0) arguing for the Oxygen Crash scenario, although I don't think it's where I got the idea from, that was years ago.

that paper is self-admittedly an amateur one; it only takes a simple calculation to shot down that theory:

The atmosphere of earth has a mass of 5*10^18 kg (source: wikipedia). Of that, roughly one fifth is oxygen, so let's make it a round number at 1*10^18 kg. The level of oxygen in the atmosphere changed with time, but 65 million years ago it was somewhat higher to what it is now, we know that from isotope measuring in rocks. Let's assume it was the same as it is now to keep a round number. There's a bit more oxygen available because some is dissolved in the oceans, but let's ignore that one.
Biomass on earth is estimated at 500 billion tonnes of carbon, meaning 5*10^14 kg (again, from wikipedia). Dry biomass is made for roughly half of carbon (living creatures have less carbon that that because they are made mostly of water, but water would not burn), so we can estimate 1.10^15 kg of oxydable biomass.
In a common alcane combustion, the mass of oxygen required to burn the alkane is roughly 3 times the mass of the alkane (actually a bit less, and biomnass is already partially oxydized, but let's do all the rounding up in favor of oxygen depletion). So, to burn all the biomass on earth it would take about 3*10^15 kg of oxygen.
But let us assume that at the time there was more biomass; let's say it was three times as abundant. Now it would take 1*10^16 kg of oxygen to burn it. Which is 1/100th of 1*10^18 kg of oxygen in the atmosphere.

So, even making the highest assumptions for oxygen consumption, we see that the KT event, with subsequent fire that burned most of the biosphere, could have depleted atmospheric oxygen level by no more than 1% - and just to be clear, that's not a reduction from 21% to 20% of the atmosphere, but from 21% to 20.79%.
And, I underline, we got that 1% under very favorable assumptions. namely, we assumed the same oxygen level of present day, when it was higher. we discounted the part of oxygen dissolved in the oceans. We assumed that there was 3 times more biomass than there is today. We assumed that all of it burned. And we rounded up all the calculations. The real values is certainly smaller than that.

Now, let us see the other claimed source, sulfur rocks. According again to wikipedia, the asteroid dug a hole 100 km wide and 30 km deep. Assuming a cilinder with a radius of 100 km and a height of 30 km (which overestimates the volume, because we are going for the most favorable approximations) we get roughly 1 million cubic kilometers of rock.
Now, assuming all that rock was pure sulfur, it would be (sulfur has a density of roughly 2 kg/dm^3) 2*10^18 kg. Sulfur combines with oxygen in practically equal wheight, so that could take twice the oxygen in the atmosphere. So, we got a plausible mechanism the oxygen depletion?

No. No, we don't. Because we're relying on too-wild assumptions. We assume that the whole crater was made entirely of pure sulfur. Would you believe that? Sulfur is fairly common, but I've never heard of anything approaching a 100-km-wide, 30-km-deep mass of native sulfur. In fact, most sulfur on earth is in the form of sulfates, which is an already oxidated form; it can't take in any more oxygen.
Even assuming a content in native sulfur of 10%, which is being *extremely* generous, we'd get that only 20% of the earth's oxygen was depleted. Which would cause the atmosphere to have the oxygen level it now has at 2000 meters of altitude, which is perfectly safe to breath even for the sick and the elderly, or they wouldn't use it in aircraft liners.
And we are still estimating that the crater was a cylinder and not a portion of sphere; we are overestimating the volume by a factor of 2 to 3. And we are not accounting that a lot of the ejecta went into space anyway, so it would not consume any oxygen, and a lot more fell into the bottom of the sea, where the oxygen level would be too low to oxydize it in a short enough time to matter for this theory.

So, I believe we can consider the "oxygen depletion theory" as completely shot down. It doesn't hold to calculations.

On the plus side, those calculations will be great for my chemistry students. I'm going to use them in my next test, they will be the hard problem for getting top marks.

[Lord Torath]

You really overstated that crater volume. A 100 km-wide crater has a radius of only 50 km, resulting in a cylindrical volume of about 235,000 km3. Which means that under worst-case conditions, the sulfur could only deplete half of the Earth's oxygen.

[Andor13]

So, I believe we can consider the "oxygen depletion theory" as completely shot down. It doesn't hold to calculations.

I have no intention of arguing with your math, but I do think you're missing the larger problem. The issue, as I conceive of the scenario, isn't that the impact itself removes the oxygen in a single pulse, it's that the combination of fire, acid rain, and a couple of years of darkness shut down oxygen renewal. It seems to be well established in the literature that the ocean surface ecology was pretty much completely shut down for centuries (to the point that full recovery had to wait 1-2 million years for radiative evolution to fill the missing niches), and there was a major immediate impact on surface vegetation (Catastrophically so in North America, less so elsewhere.) So between the complete loss of vegetation in North America (short lived, in all probability, but the fossil record indicates trees were wiped out, and replaced by ferns for some centuries, and grasses didn't exist yet so a big dip followed by a slowish recovery) the shut down of oxygen production of oceanic algae for some centuries, and some loss of production from surface vegetation on the remaining continents for some years due to some combination of fire, acid rain, and dust shroud induced darkness. Free oxygen is, of course, constantly being consumed by both biological processes and surface oxidation, without constant renewal it will self-deplete rapidly.

So the question is, could the initial pulse of oxygen consumption you so nicely calculated, combined with the short to mid term interruption of renewal methods, plausibly deplete, say, 30-40% of atmospheric oxygen? That would be more than enough to wipe out many already stressed megafauna species, and the following ecological disruption could finish off the rest. Could an ill timed burp by the (erupting at that time) Deccan trap volcanos have provided the kicker of another few years of darkness?

[Solaris]

Being a herd animal does not render one domesticatable or good at draft pulling. Llamas are domesticatable and can't be used for plowing or pulling heavy loads, zebras, rhinos, hippos and giraffes can pull loads and are not domesticatable.

And?
Your hypothesis is pretty weak. Dogs are used as draft animals. Last I checked, they don't have hooves. Some elephants are semi-domesticated, and neither do they. You also haven't established a causative relationship, merely a correlative one. By the same logic, my wife is responsible for increasing rates of diabetes in the south.


I don't know how useful that is though. Cephalopoda could easily produce an intelligent, self-aware creature that couldn't make much use of tools or agriculture. My main argument is that it takes a laundry list of traits for civilization to occur, and these are unlikely to occur together. Dolphins being the modern example.

But why did you put hooved draft animals on that list? We have civilizations that never domesticated animals, much less hooved draft animals.


As many have pointed out, an industrial civilization would leave traces all over the place. A preindustrial civilization would leave smaller traces, and it is not impossible that those would not be detected. So, we could not really rule out that there was a civilization, but it collapsed before it reached industrial technology, right?

Except... how would it collapse?

You assume that the species would be as adaptable as we are.
Our own history is littered with the remains of our siblings, cousins, and ancestors who were not as adaptable as we. I'd say it's pretty easy to imagine a scenario like any one of those that nearly did the hominids in, but the sapient saurians simply didn't have what it took to adapt and overcome.

[King of Nowhere]

I have no intention of arguing with your math, but I do think you're missing the larger problem. The issue, as I conceive of the scenario, isn't that the impact itself removes the oxygen in a single pulse, it's that the combination of fire, acid rain, and a couple of years of darkness shut down oxygen renewal. It seems to be well established in the literature that the ocean surface ecology was pretty much completely shut down for centuries (to the point that full recovery had to wait 1-2 million years for radiative evolution to fill the missing niches), and there was a major immediate impact on surface vegetation (Catastrophically so in North America, less so elsewhere.) So between the complete loss of vegetation in North America (short lived, in all probability, but the fossil record indicates trees were wiped out, and replaced by ferns for some centuries, and grasses didn't exist yet so a big dip followed by a slowish recovery) the shut down of oxygen production of oceanic algae for some centuries, and some loss of production from surface vegetation on the remaining continents for some years due to some combination of fire, acid rain, and dust shroud induced darkness. Free oxygen is, of course, constantly being consumed by both biological processes and surface oxidation, without constant renewal it will self-deplete rapidly.

So the question is, could the initial pulse of oxygen consumption you so nicely calculated, combined with the short to mid term interruption of renewal methods, plausibly deplete, say, 30-40% of atmospheric oxygen? That would be more than enough to wipe out many already stressed megafauna species, and the following ecological disruption could finish off the rest. Could an ill timed burp by the (erupting at that time) Deccan trap volcanos have provided the kicker of another few years of darkness?

Already taken into account



Our atmmosphere has enough oxygen that we could still breath for a few millennia even if all photosynthesis suddenly stopped. Considering that most animals - oxygen consumers - also died, then the drop in oxygen level wasn't severe, or even significant enough to be felt.



Again, it's something that can be calculated roughly. A human consumes about half a kilogram of oxygen daily. that's about twice our body mass per year. And we established that in the atmosphere there is about one ton of oxygen for every kilogram of living matter. Oxygen would last 500 years if all living matter was humans, but humans are hot-blooded, they use up a lot of oxygen; most other animals have smaller requirements, and plants need even less.

There was a worldwide firestorm, followed by quick death of most plants - acidic rain taking its toll on those that managed to survive in the lower sunlight -, followed by death of herbivores and then of carnivores. The climate cooled down really quickly, and then it suddenly heated up. that was a lot already. but there was no significant oxygen depletion from the atmosphere.

And all that stuff that happened is something that humans would have survived, even with paleolithic level of technology. we are pretty badass.





You assume that the species would be as adaptable as we are.
Our own history is littered with the remains of our siblings, cousins, and ancestors who were not as adaptable as we. I'd say it's pretty easy to imagine a scenario like any one of those that nearly did the hominids in, but the sapient saurians simply didn't have what it took to adapt and overcome.

i already conceded that point. A sapient species is adaptable by virtue of its technology - just the capacity of using fire and making rudimentary clothing gives better climate tolerance than virtually anything else, and spears plus teamplay put you straight on top of the food chain - but yes, there are limitations to how much prehistoric technoology lets you adapt. I am reasoning in terms of likelyhood, not certainty.

[Bohandas]

If we could work out how much oil should have formed over the Earth's history, and how much we've used, and how much is left, and then compare the first figure to the latter two, if we found that there's a bunch missing an unaccounted for, that might suggest a previous industrial civilization.

[Lvl 2 Expert]

Our estimates of how much oil there still is and how much was ever formed though are almost completely based on what we've found. As far as I know there are no good formulas for how much oil should be forming formed independently from our studies of how much there is. It also varies greatly by period. Much of our oil is from the carboniferous, the best oil producing geological period.

Interesting about that last tidbit is that the carboniferous was +-360 to 300 million years ago, easily long enough before any possible dinosaur civilization and even the end Permian extinction event for that oil to have been formed by then. (I think estimates are it takes a few hundred thousand years or so to form oil, so even under sub-ideal circumstances it should have been a done deal at that point.) So any civilization at those points certainly didn't exhaust the supplies.

[Andor13]

Already taken into account

Again, it's something that can be calculated roughly. A human consumes about half a kilogram of oxygen daily. that's about twice our body mass per year. And we established that in the atmosphere there is about one ton of oxygen for every kilogram of living matter. Oxygen would last 500 years if all living matter was humans, but humans are hot-blooded, they use up a lot of oxygen; most other animals have smaller requirements, and plants need even less.

There was a worldwide firestorm, followed by quick death of most plants - acidic rain taking its toll on those that managed to survive in the lower sunlight -, followed by death of herbivores and then of carnivores. The climate cooled down really quickly, and then it suddenly heated up. that was a lot already. but there was no significant oxygen depletion from the atmosphere.

And all that stuff that happened is something that humans would have survived, even with paleolithic level of technology. we are pretty badass.

Although as someone (I think you) noted the rise in CO2 from the disruption of the oxygen cycle would be problematic long before the total depletion of O2. Plus the Dinos were by modern estimation hot-blooded creatures used to an atmosphere richer in oxygen than our own, they may have been more vulnerable than we are.

And yes, we are pretty bad ass, but I honestly feel surviving an event like the Chicxulub Impact for neolithic us would come down to luck. Most of the population is coastal, and they would pretty much be a write-off. Between the tsunamis of the event itself and the collapse of the oceanic food chain, it's really only the inland populations to think about. The years of cold are going to kill off a lot of the population at high latitudes (although they may be able to eek out a living on scavenging carcasses for a time) and the following years of heat are going to brutalize the lower latitudes. Between the fires, the acid, the ecological shifts, the darkness, the cold, the heat, etc every single group is going to face multiple potential extinction threats and they need to make the saves every single time.

We know of more than one advanced human population dying off within recorded history to far lesser catastrophes (Greenland and Roanoke off the top of my head.)

[Tvtyrant]

But why did you put hooved draft animals on that list? We have civilizations that never domesticated animals, much less hooved draft animals.


You assume that the species would be as adaptable as we are.
Our own history is littered with the remains of our siblings, cousins, and ancestors who were not as adaptable as we. I'd say it's pretty easy to imagine a scenario like any one of those that nearly did the hominids in, but the sapient saurians simply didn't have what it took to adapt and overcome.

Name one? We have lots of cultures, we have no civilizations. In the classic sense of developed cities and terraforming, which would be required for us to find their remains and be able to differentiate them from other animals.

Dogs and llamas are both capable of pulling carts, neither can be used for agricultural plowing. Hooved animals have differently shaped spines then none-hooved animals which allows them to pull and carry heavier loads; Elephants are a case in point where heavy labor badly damages them.

Strike that, I'm willing to concede here. I don't think a civilization whose terraforming is widespread enough to be noticeable after 60 million years would occur without plows, but we do have some major ones that occurred.

[Bucky]

Except neither is quite what you claimed... One is just a uranium site dense enough to start nuclear chain reactions (barely) and nothing indicates it must or even should be a waste site, and the other is basically a special kind of volcanoe. Are all volcanoe proof of a mining civilization?

I'm not claiming proof of an ancient civilization. I'm claiming that, if an ancient civilization did make use of nuclear reactors, or deep mineshafts, we'd be able to recognize them hundreds of millions of years later. We know that because of natural reactors and shafts.

[Ravens_cry]

Whether there was ancient civilizations of non human sapients or not, the fact there was a naturally occurring nuclear reactor at one point in Earth's history is just . . . awesome:smallbiggrin:.

[NRSASD]

Whether there was ancient civilizations of non human sapients or not, the fact there was a naturally occurring nuclear reactor at one point in Earth's history is just . . . awesome:smallbiggrin:.

100% agreed!


Something I'm surprised that hasn't come up yet is pottery and ceramic remains. They are pretty darn indestructible by heat, decently durable, have no naturally occurring look alikes, predate agriculture and settlements by 20K years, and are almost ubiquitous throughout human civilization. If there were a sentient species of any appreciable size and complexity, I'd expect to have found at least 1 pottery sherd by now, if not giant beds of the stuff like this (https://fineartamerica.com/featured/devonian-fossil-gorge-fossil-08-cynthia-woods.html).

[danzibr]

Ah, but what if the Dinosaurs crashed a rock in to the planet in some misguided attempt to win a war?:smallcool:

Realise you're not serious, but if they were advanced enough to do that then we're talking a civilization with space travel capability, and things in space tend to last a *lot* longer than stuff on the ground--something placed in a geostationary orbit 60 million years ago would probably still be up there!
Or Sephiroth.

[Dodom]

Humans are leaving a bunch of other durable traces, namely:
[...]
* Splicing genes from some organisms into unrelated organisms; this will remain detectable to future molecular phylogeneticists as long as those organisms' descendants survive
[...]

That might not be easily detectable. Horizontal gene transfer (Wiki for definition (https://en.wikipedia.org/wiki/Horizontal_gene_transfer)) turned out to be more common than expected, so there's a background noise of naturally misplaced genes, and the number of surviving modified organisms might not be sufficient to find a pattern.