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65 million years ago, a mass extinction event (likely caused by the Chicxulub Meteor) wiped out the dinosaurs, and their remains were hidden from us for millions of years.

Humanity was not around at the time, and there were no major societies or civilizations.

But what if there had been? What if there had been a race or civilization at that exact moment in history, approximately like our own currently, but with an advanced spacefaring device that allowed them all to leave at once, leaving only behind the ruins of their society?

What would be left over from their society, assuming they used similar methods of construction and had similar cities, factories, and historic periods to our own, that we would be able to find in modern times?

UPDATE:

To clarify, there would be no fossil records of the actual civilization (all their dead are cremated before departure, and their evacuation is 100% complete, pets included) only the artifacts left behind by their civilization (all habitats, entertainment, and food are provided on their escape vehicles, but everything they had is left behind). And they are not humans, but approximately close enough bipedal creatures that they're very similar to humans.

UPDATE 2:

Assume that they won't be doing anything to impact our world. They could be coming back tomorrow, settled on other worlds, gone forever in a horrible accident, but they can't be having an impact on our world, and we likewise aren't going to find evidence of them from anywhere but here.

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    $\begingroup$ See the Sapience Pulsar question and answers. $\endgroup$ – Serban Tanasa Mar 22 '15 at 16:45
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    $\begingroup$ Oooh, this one too: Could we find a Dinosaur Civ in space? $\endgroup$ – Serban Tanasa Mar 22 '15 at 17:09
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    $\begingroup$ For clarification: this society posses a space-faring device, but do they also possess a "detect imminent mass extinction event" device? Because that might be a handy thing to have in order to use that space-faring thing. If not, we should probably begin looking for a spaceship buried in some clay/rocks somewhere. $\endgroup$ – Ellesedil Mar 23 '15 at 17:33
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    $\begingroup$ @Ellesedil Yes. They call it a "telescope" and "oh goodness that asteroid is headed straight for us". $\endgroup$ – Zibbobz Mar 23 '15 at 17:35
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    $\begingroup$ @Lohoris I don't think that's necessary. I would rather not include it, as it would distract from the focus of the question being artifacts left behind - whether they're coming back tomorrow, gone forever, disappeared from existence the moment they left or any other reason doesn't matter, just what was left behind by them while they were here. $\endgroup$ – Zibbobz May 22 '15 at 13:12

14 Answers 14

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An industrial civilization on the same technological scale as our own would leave a layer of odd chemistry in the rock, ratios of isotopes out of whack. Here are some possibilities.

Fossil fuels are made of very old carbon where most of the radioactive carbon-14 has decayed into carbon-12. Our digging up and burning of fossil fuels is putting far more carbon-12 into the atmosphere than carbon-14 than would by natural processes. This change in the ratio of carbon-12 to carbon-14 would be detectable in the industrial layer... UPDATE as @Keith correctly points out carbon-14 would have decayed to undetectable levels in less than 100,000 years.

Similarly, there would be elevated levels of other compounds locked up in fossil fuels such as sulfur, mercury, uranium, thorium, arsenic, and other heavy metals.

Any nuclear industry would leave behind nuclear waste. Some waste products are very short lived, but others like Zirconium 93, Caesium-135, Palladium-107 and Iodine-129 have half lives in millions of years. In addition, the stable products they decay to (lead, iron, xenon) would be elevated.

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    $\begingroup$ Note that all carbon-14 would have long since decayed over such a time period. Carbon dating gets difficult even after only 50k years. $\endgroup$ – Keith Mar 23 '15 at 0:41
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    $\begingroup$ Could any 'Fossil Fuels' have been available at that time? $\endgroup$ – user2448131 Mar 23 '15 at 1:14
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    $\begingroup$ @user2448131 65 million years ago is pretty late, dinosaurs were running around 200+ million years ago and reptiles for 300+. Fossil fuel isn't really dinosaurs anyway, it's mostly plants, and run as old as 650 million years. $\endgroup$ – Schwern Mar 23 '15 at 13:40
  • $\begingroup$ @Keith Hmm, good point. $\endgroup$ – Schwern Mar 23 '15 at 13:40
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    $\begingroup$ Finally found info on coal creation time,so there would be coal available 65 mya, still dont know about oil, however. $\endgroup$ – user2448131 Mar 23 '15 at 15:29
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Dinosaur fossils are dug up all of the time. Including things like fossilized teeth. I wonder what researchers would say to a gold nugget embedded in a tooth.

Things like clothing, watches, ... might leave impressions in the stone, just as there are fossils with skin or feather impressions (wikimedia link to Archaeopteryx).

What happens to ceramics in sedimentary stone? At least impressions, I'd guess.

Nuclear waste could make people wonder, or come to completely wrong conclusions about the natural formation of radioactive materials.

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    $\begingroup$ Nuclear waste only has a half-life of around 25 thousand years though. I know that's a fairly big number for an 'only', but compared to 65 million years, it's a drop in the pond. $\endgroup$ – Zibbobz Mar 22 '15 at 19:57
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    $\begingroup$ @Zibbobz Treating "nuclear waste" as a single thing is like treating "garbage" as a single thing. Nuclear waste is made up of all sorts of different materials with different half-lives. Some last for seconds, some like Iodine 129 have a half life of 15.7 million years. $\endgroup$ – Schwern Mar 22 '15 at 22:30
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    $\begingroup$ @Dronz with a half-life of 25,000 years, after 65 million years there will be around 10^-780 percent of the original left. If the entire Earth had been radioactive with that half-life, it would be unlikely for a single atom of the original radioactive substance to remain after 65 million years. $\endgroup$ – Rob Watts Mar 23 '15 at 17:03
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    $\begingroup$ @RobWatts Good point, except it decays to something still quite unusual (e.g. Pu-239 decays with half-life 24,110 years to Uranium-235, natural rarity 0.0072, half-life 703.8 million years), and the containment facility itself is also going to be durable and unnatural-looking, and since the question is about whether it will de detectable to future archaeologists or not, I would think the remainders would be, as long as they haven't been destroyed by mishap. $\endgroup$ – Dronz Mar 23 '15 at 18:34
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    $\begingroup$ Point in case is the Oklo region in Gabon. The Uranium ores there have acted as a "natural reactor" in the Precambiran, two billion years before. They can still tell, by the proportions in which various isotopes are found in the ores... $\endgroup$ – DevSolar Mar 24 '15 at 8:18
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The most likely remnants would be Space Artifacts.

65 million years is such an insanely long time that almost anything left will be wiped out, either by natural processes, chemical reactions (oxidation, etc), or even geological events - the continents of the world are very different now, those changes could have destroyed things. Not to mention that the meteor event itself would cause significant destruction.

Now, it's unlikely that you'd find anything in orbit. But you might find ancient satellite remnants in some of the Lagrange points - these are gravitationally stable points between the Earth and Moon, and it's possible they'd collect some of the Dino's old satellites. You probably wouldn't get something entirely intact - micrometeorites add up over 65 million years - but you could get parts that are clearly artificial and non-human. Another possibility here is the Earth-Sun Lagrange points, which are further away.

More likely to be intact would be a space base somewhere in the solar system. Many other bodies are non-active geologically, which will help preserve a base, and if it's buried it's protected from micrometeorites. These could easily be wiped out by a larger impact, though.

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    $\begingroup$ Although I like the answer, I still think that 65 million years is, as you said, such an insanely long time that not even satellite remnants could survive. The probability is just too high that they would eventually collide with other things and leave their orbit. $\endgroup$ – Bogdan Alexandru Mar 24 '15 at 7:42
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Most of the answers so far are focusing on accidental evidence. But since the civilization was able to leave, they obviously knew the event was coming with some amount of lead time. This makes it quite likely that they would've attempted to leave intentional long-lasting evidence of their presence. This might be messages encoded using long-lasting isotopes as others have mentioned, or perhaps messages left on the moon itself, where the materials are less likely to break down.

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    $\begingroup$ Though I intended to ask about evidence that might be left behind unintentionally, this is a good point to make, and I'll even +1 it for thinking outside the box. $\endgroup$ – Zibbobz Mar 23 '15 at 16:42
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There would be very few, if any surviving artifacts remaining if there was an advanced humanoid society at the time of the dinosaurs.

There would have been very significant Earth changes between that time and now. If we traveled back to that time, we would have a hard time recognizing the world. Continents would not be in the same place as they are now. Climate and atmospheric conditions including weather patterns would be alien to us. Sea levels would be drastically different. There could be entire landmasses existing which no longer exist today. Mountain ranges that we know today may not have formed yet. Other features that we know well today would not be present like the Great Lakes, Long Island, and all of the other geological formations which were formed by glaciers during the ice ages.

Because of these differences, it would be very tough to pinpoint where to even look for these civilizations in the modern day, even if we knew where they were in the past. They could be deep underwater, or at the top of a mountain, or they could have been vaporized by a volcano, or a meteorite or asteroid collision. These cities could have also been sucked into a subduction zone and melted into the Earth's crust.

If this civilization attempted to come back to Earth after all that time, there would most likely not be any remnants of their civilization. It would all be buried deep in the sands of time.

It may be possible that there could be fragments of their civilization remaining. However, it would be difficult to identify these remains as nothing more than an oddity. Over the years, there have been several claims about people finding artifacts that supposedly came from extreme antiquity. Most of these claims have proved to be dubious or completely unfounded. They are usually just the result of elaborate hoaxes brought on people with an agenda.

Even if legitimate evidence was found, it would be very difficult to prove that it was made at the time of the dinosaurs. There could be some form of advanced technology available which could accurately date these remnants.

There would be very little evidence of the buildings themselves. Any structure made out of wood or metal would have returned to its natural state long before modern humans could lay eyes on it. The only thing that may be left over are features made of stone which may have been buried millions of years ago and preserved.

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  • $\begingroup$ This is a particularly good answer, though it's coming in surprisingly late. Is there any particular reason you say stone structures would be better preserved than metal? $\endgroup$ – Zibbobz Mar 25 '15 at 17:08
  • $\begingroup$ @Zibbobz After the city was evacuated, the buildings in it would eventually collapse due to earthquakes. The metal structure inside of them would be exposed to the elements and oxidize away. There would be very little evidence that there was metal there at all. There may be some bits that resemble iron ore, but the results would be inconclusive whether or not they were human made or naturally occurring. The stone facade and foundation may still survive as long as they were not exposed directly to the elements for a long period of time. $\endgroup$ – Jason Hutchinson Mar 25 '15 at 18:53
  • $\begingroup$ I find that fairly satisfactory, except the last point. Why would the stone façade and foundation not be exposed to the elements over a period of 65 million years? $\endgroup$ – Zibbobz Mar 25 '15 at 18:55
  • $\begingroup$ @Zibbobz there are many ways the city could be buried. If it is near a very arid place, then sand can blow in and cover it. In a tropical setting, vegetation will grow over it and eventually bury it completely. Humans may bury it for various reasons. It could also be completely underwater as well. If it was exposed directly to the elements, the freeze-thaw cycle would break it apart, wind driven sand will sandblast it, acid rain would melt it kind of like how dripping water will dissolve a sugar cube. The best hope for survival would be in a very dry desert buried deep under sand. $\endgroup$ – Jason Hutchinson Mar 25 '15 at 20:27
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There would be abundant fossil evidence of their buildings, tools, art, technology and trash. As abundant as other fossil evidence from the same period, at least, which would be plenty to show many clues about the civilization.

Consider: How do we know that dinosaurs existed at all? Fossils from their time. We also have fossils of plants, insects and microbes from even before their time. If as you say they left behind entire cities, and had a pre-modern history, there would be many fossils left of all the stuff they built and made and wore and littered and lost and so on.

The oldest insect fossil is about 400 million years old. Here's an insect wing from over 100 million years ago: http://en.wikipedia.org/wiki/Necroraphidia#/media/File:ZooKeys-204-001-g004_Necroraphidia_fig1.jpg

Given the right circumstances, such as ash or mud suddenly covering a town and later being uncovered, there could be decent archaeological sites too, although they might be sites of fossils and impressions rather than intact objects. Major constructions could leave recognizable traces too: roads, aqueducts, industry, dumps, scrapyards.

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    $\begingroup$ Whether it would be abundant or almost nonexistant depends very much on how long this civilization flourished. The Dinosaurs existed for over 100 million years, and we have only a handful of good fossils of most larger species. if that civilization developed over just a few thousand years like ours, I don't think there would be much evidence left. $\endgroup$ – Michael Borgwardt Mar 24 '15 at 12:16
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    $\begingroup$ If their "civilization" produced as much garbage and litter as we do, I'd think it'd be spread practically everywhere about as much as ours is, wouldn't you? $\endgroup$ – Dronz Mar 24 '15 at 15:56
  • $\begingroup$ It would be spread everywhere 65 million years ago. You are not even remotely able to grasp just how long that is and how small the chances are of any object persisting that long. $\endgroup$ – Michael Borgwardt Mar 24 '15 at 16:14
  • $\begingroup$ Seems to me that the chance of finding some evidence in a fossil has a lot to do with how much of the surface of the planet contains some evidence. Given the amount of surface area we have littered with evidence, I'd say some things would be found by people doing the amount of archaeology that we do. $\endgroup$ – Dronz Mar 24 '15 at 16:21
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    $\begingroup$ A very good point, but they only left their corpses. Typical modern people daily produce many waste items each, and litter some of them, and we have all these large buildings and roads and vehicles and so on all over the place. How many thousand (or million?) little objects are created for each modern human? In terms of items that can be found, I think we do have the potential to catch up to the same ballpark, at least. And again, I don't think it's just a combination of numbers, but spread of location. $\endgroup$ – Dronz Mar 24 '15 at 16:52
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Some salt deposits were created 250 million of years ago in geologically stable areas. They have remained undisturbed until humans start burying the waste of nuclear centrals, see why the U.S. government chose salt mines to bury long-lived radioactive wastes.

It would be the most obvious place to bury artifacts for the benefit of later civilizations. With no running water and humidity, you could even get away with storing paper!

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    $\begingroup$ Just a hint: salt mines were salt mines first, and occasionally chosen as nuclear waste deposits later. For all i know noone has yet dug into an "untouched" salt deposit only to create a waste deposit. $\endgroup$ – Burki Apr 13 '16 at 7:11
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Great question.

Many of the products of civilization could survive, particularly large structures, and items of particular metals.

I'd expect most of these to be deeply buried in strata, much of it inaccessible.

However, if the civilization was global, some areas of land surface would survive and hence be able to show traces. For example, most of the Australian continent was around 65M years ago or longer.

It's not obvious to me that one should look in the regular fossil beds, but I stand to be corrected. Such sites have a duration that might be very long relative to a civilization. Presuming that they represent swamps or river or lake beds, I guess a certain amount of junk might end up there, but not necessarily.

I agree that isotope anomalies the nuclear industry might be an indicator. However, if one does not find the site of a reactor or accident, I do not know that the overall environment would leave evidence in the strata.

In conclusion, I suspect evidence would be somewhat hit and miss with not a lot to show for it today. At the same time, I think that means that a civilization of our current level of industrialisation or above would have left a fair amount of evidence scattered around.

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  • $\begingroup$ Consider erosion as well as things being covered in dust and plants. Take a look at pictures of abandonned structures, and how fast they are being covered in just about everything. Even after 25 years you can see massive wear. now make that 65'000'000 years... no, you definitely would not see anything on the surface. $\endgroup$ – Burki Apr 13 '16 at 7:14
  • $\begingroup$ Bingham canyon mine will fill in in 65 million years, but anyone with a radar will be able to tell that it is un-natural. Maybe not the best example since it could be filled by volcanism, but I'm sure there are other enormous strip mines in more geologically stable areas. $\endgroup$ – kingledion Oct 21 '16 at 13:57
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I've seen this question asked elsewhere many years ago. The most convincing answer for me was that EARTHWORKS would be fairly easy to find millions of years later. Any advanced civilisation would rely on metals and getting them from the ground often involves opencast mining - leaving a huge pit in rock which will tend to be filled in such a way that its purpose is clear to future archaeologists.

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    $\begingroup$ I would think various ice ages and weathering effects would leave them indistinguishable from natural formations. $\endgroup$ – Schwern Mar 24 '15 at 16:01
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The easiest way to detect such a civilisation after 65 million years is to look at its effects on other life. You'd be looking for geological evidence of a mass extinction 65 million years ago, like the one that's in progress at present, as the dinosaur civilisation expanded and used up the available biological resources for itself.

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  • $\begingroup$ Could you expand on this - it sounds like you're suggesting the type of impact a civilization would have on organic life outside that civilization, which is a reasonable and interesting idea, but could use some elaboration. $\endgroup$ – Zibbobz Apr 13 '16 at 13:23
  • $\begingroup$ So it wasn't the meteor? it was this ancient civilization that caused the mass extinction 65 million years ago? $\endgroup$ – Mr.Mindor Apr 13 '16 at 14:54
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It seems to me that the subsequent evolution of Velociraptor, some million years before dinosaur extinction, would be the place to look for potentially intelligent species. They were effectively bipedal, forearms with claws for manipulation, and social (hunted in packs). One idea: if some brainy dinos survived (or anticipated) a mega-collision, other than leaving Earth, they could have moved underground? I speculate that extraterrestrials described with large eyes are evidence of subterranean life (after all, where could you live on Mars or on bombardment-likely planets but underground? John Caddy

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Mines and mineral deposits. Many of the mines humans have exploited through history were formed long before 65 million years ago, which means those resources would have been there for some civilization to exploit, but yet those deposits were untouched prior to humans working them, indicating no one else had been around to exploit them first.

If one had, that's a huge honking clue. You'd find things like underground deposits where what should be the richest ore was missing, replaced by what looks like filled-in tunnels that show unnatural regularity. You'd have surface deposits where, again, the richest ores were missing, leaving a halo of surrounding lower-grade rock surrounding a plug of sedimentary rock, what you'd expect if someone had been open-pitting and the mine had gradually been filled with sediment. You'd see areas of very fine mudstones with disseminated minerals that looked in no way natural, the remains of tailings. And so on and so forth.

Now, mines tend to take up a geographically small area so the odds of just stumbling on the remains of one a few million years old are small, but their locations aren't random; they're determined by geology a lot older than this hypothetical civilization, and where they'd mine is where we'd currently be looking for things to mine. Someone, at some point, would have stumbled on something so freaking anomalous that everyone would know about it.

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A civilization advanced to the point of leaving the planet before a catastrophy might as well have the means to restore parts of it to its previous state. They could, for example, build some sort of "Noah's Ark", where eggs and embryos (or the genetic information) of the most threatened species could be stored, allowing them to repopulate the Earth after some time. In this scenario, the "leftovers" of such a civilization would be dinossaurs surviving up to our time.

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  • $\begingroup$ While possible, I've edited my answer recently to reflect that there is no remaining part of the species left - they have all departed, for one reason or another, and for the sake of this question there is no part of the species that was left behind. We are also assuming that despite the technology to evacuate the planet, they are otherwise identical to our own culture's technology level today. $\endgroup$ – Zibbobz Mar 24 '15 at 20:31
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Imagine if the human civilization suddenly ceased to exist. What would a future geologist or paleontologist find of our civilization. Assuming it is 65 million years after we're gone, not much. By this time, metals have been corroded, concrete structures such as sidewalks and damns has been eroded away and plastics have been biodegraded. Most of our satellites have fallen back to earth by this time. Unless for some miraculous situation where a bunker or sanctuary had survived for this amount of time, the only safe place is space.

However, some of our spacecraft, including the voyagers would survive to this time, assuming nothing went wrong.

Even if a dinosaur civilization did develop in the Cretaceous, any surface structures would be long gone. A subterranean bunker would stand a better chance of surviving, especially if it was far enough away from fault lines where volcanoes and earthquakes wouldn't be a problem.

As a space faring species, if they were as advanced as us, the only place they could really go is mars, but even that is unlikely.

However, no one can say with certainty that a dinosaur civilization did NOT exist.

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    $\begingroup$ The lunar landers of Apollo would definitely NOT be "virtually intact" after 65M years. Compare Can I borrow a lunar rover? on Space Exploration. $\endgroup$ – a CVn Oct 21 '16 at 7:08
  • $\begingroup$ I think you severely underestimate the capabilities of modern-day archaeologists to uncover buried relics. And overestimate the decay rate of large structures, as well as the impact they would have on archeological finds. $\endgroup$ – Zibbobz Oct 21 '16 at 13:12
  • $\begingroup$ Though it is true the lunar landers would not be Virtually intact, because of the lack of wind and flowing water on the moon, the lunar landers could surivive, unless they were smushed by a meteorite impact, or suffered damage or destruction from some other force. $\endgroup$ – Fabio Oct 21 '16 at 14:02
  • $\begingroup$ @Fabio Several hundred degrees temperature swings over periods of weeks is definitely a force to be reckoned with. Solar radiation is another force that can break down materials over time scales far shorter than we are discussing here. $\endgroup$ – a CVn Oct 21 '16 at 14:14

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