What if we aren't the first technologically advanced society?

[PB666]

When one talks about archeology and paleontology in a statistical context their are tangible and intangible aspects. So for instance, if the civilization was of dinosaurs they would be rather easy to detect because the long bones are so massive, forces that cause demineralization as part of ubiquitous calicium turnover last long enough for the bone to often end up deep in a non-biologically active layer where fossilization will preserve them and where gnawing animals lack access. This is a tangible aspect, and we can think of freeways and the concrete foundations of skyscrapers in the same context, in the case of the second, for example many have footings 30 to 40 feet under the lowest floor layer in a basic dead zone where compaction is so high oxygen and nutrient flow is basically zero.

We have detected many species much smaller than humans going back tonthe cambrian, thats 650 million years and the fact we don't detect things earlier is not do so much to our techniques or land masses, but to the lack of vertebrates and infrequency of shell forming animals. There are many areas of the world, for example the back yard were i grew up, you have a rock in a trech you are digging, you pry it out of the ground often busting it, right in the middle will be a massive bivalve shell, its kind of hard to miss the evidence for bivalves even if they are mot as big as dinosaurs there were just so many of them. Thats another tangible. 

So we have two things, rather large long bones and lots of chances to be fossilized. That places humans on the scale somewher between a smaller dinosaur and bivalves for being detected, paleontologically speaking. And archaeologically speaking at the top of detectability, above amber forming trees and the middens of burrowing animals, and caches of cave dwelling predators. So we have 3 big detection worthy tells. 

The we can talk abou intangibles. How can one have an intangible tell. Well it works like this, if we look at the haploid DNA of eucaryotes we can do coalescence analysis using the 2N rule to tell population size. This allows us to basically see the size of the human population back about 100 to 200 thousand years ago, with X-linked DNA its a litle bit more difficult but its posdible to see back almost a million years ago. Human population, including the various late achaic homo sapiens were a part of a numerically small population to about 60,000 years ago, after which size grew to beyond an extent which no longer obvious limitation to the growth of mtDNA diversity. The population constraint on diversity was so obvious it was pointed out by Brown in 1980s that humans populations look, in terms of diversity, like a small subpopulation of another ape species. And yet from the period  from a million years ago to 60,000!years ago we find lots of archaeological evidence, From homo erectus there are stone axes is Africa, the Bose formation in china. From hiedlebergensis there are eraly european stone tools, from neandetals there are a great number of lithic artifacts from the classic and levantine associated periods. There is something like 500 physical neandertalindividuals represented by 'fossile'record despite the fact that the genetics suggest the entire population size was below 10,000 individuals for most of the time Neandertals existed. So we can intangibly argue that even primative humans with a much lower archaeolical footprint than ourselves left a visible footprint. Even before this we have bith archaeology going back 2.6 million years and bones delimited ny ardipiticus ramidus from 4.5 to less than 6 million years with White concluding that the chimp human most recent common ancestor should be in that 6 to 8 million year range.

what are the comparables? We actually have a good one believe it or not. Chimpanzees are a diverse population of apes currently represented by two named species with trivial interbreeding and one species with three subspecies. Mitocondrial DNA diversity goes suggest a rather large population for the last 2 million years, a population in the millions, a magnitude or more larger than homo over most of its existence. Even if we assume a MDT of 5 million years as V. Sarich suggests when one looks at the paleontology and achaeologicgy of pan from the prehistoric period going back to 4 million years there is virtually nothing. There are a few finds that might be chimp, but nothing definative. The chimpazee paleontological tell  is less than 1/100 that of humans given predicted population size, its about par with the apes. For ancient gorillas we only have found teeth. 

Humans have an powerful intangible tell about them, we bury our dead, pack them in shell middens, place them in caves, or bury them in metal boxes; chimps don't do that. This aspect is also see for desinovans, neandertals and homo erectus. We we bury them we often add achealogy to go along with it, a favorite pet, a favorite axe, or some other trinket. This intangible aspect of our nature makes it very difficult to miss our presence in the archealogical record, we stand out like a big red flag, even in our most primative form we stand out above like species. These burials are everywhere, LM3 australial, Kiazuka in  japan, comparables from late paleolithic in France, Bog men of Ireland, Liang bua in Indonesia, Narmada India, Dmanisi georgia, Shenadar Iraq. Whats even more telling is we often bury our dead in ways that make their bones stand out. There was once a tradition of defleshing humans and then burying them. This gets tid of alot of a ids that degrade bones,mwith or without acid burying humans in a shell mound,mthe shells scavenge the acid making for a great bone preservation method. 

Our artifacts also make for interesting tells. For example, earthenware pottery of the jomon makes for great presentation. You find pottery from 4000 to 8000 years of age in japan that looks almost like the day it was made. There was a cypress cover i saw from japan that was 2,000 years old by radiocarbon, did not yet have a patina on it. But then you add glazing and refiring of the pottery, for example the large ceremonial platters used by Japenes during gatherings survived the Nagasaki atomic blast, blistered on one side and in perfect condition on the other. The density of sites in some areas are amazing, in both Japan and Oaxaca its hardcto build without stumbling onto a site.

Even more compelling is that one of the primary features of ancient geology and that is the disruption of layers. We have heard of blind faults, that is a feature in the recent geology that we cannot see. In Japan it might be called blinded faults. On at least two occasions humans have actually buried the faults and forgot about them. This is not hard to miss once you cut a trench through the fault line, you see a fault (noted by the position of a bedrock layer) move by three feet and you have four feet of very nice top soil on one side and one foot of soil on the other. Intensive agriculture is hard to miss, it perturbs the natural layering, in areas such as nothern carolina it depletes the soil of humus, evetually depleting the soil of iron and otger pigmenting molecules. In Asia it would be difficult to miss a trench through a volanic overlay where, underneath you have terracing and fossilized rice stubble. 

So the basic answer here is this, humans are not just some species of pack rats that leaves the occasionsl middens, or some beaver that builds wooden dams and lets them rot. We are the kings of Earth modifications. We disrupt just about every aspect of natural geological evolution you can think of. You can see our activity from space, the great wall? no? Look at the mouth of the Mississippi. Look at the netherlands, how aboit the Panama canal. Still not enough, lets throw in mega fauna extinctions, surely that would cause a second look. What packrat midden can survive a nuclear blast? 

Yeah, the answer is that there were no previous advanced civikizations and, no; we would not miss their archaeology.

[kerbiloid]

25 minutes ago, PB666 said:

there were no previous advanced civikization

A native one. Nothing prohibits an advanced guest civilization from building their outposts if they like.

Edited July 5, 2016 by kerbiloid

[PB666]

55 minutes ago, kerbiloid said:

A native one. Nothing prohibits an advanced guest civilization from building their outposts if they like.

Whose guest, i dont remember inviting any aliens. 

So alien civilizations comes and settles in our late heavy bombardement period, not very smart aliens. 

 

[todofwar]

1 hour ago, kerbiloid said:

A native one. Nothing prohibits an advanced guest civilization from building their outposts if they like.

Maybe the great dying was the result of terraforming attempts that got shot down by the alien greenpeace  (greypeace?) after they had already killed everything. But I think a small couple oft thousand strong settlement could easily go unnoticed if the effort was abandoned early. We're looking at maybe a few thousand tons of refined material, that can easily vanish, with a low chance of being dug up. Even if it was, a small set of artifacts that we don't recognize would be dismissed as an anomaly. Studied and thought about sure, but unless you recognized the mun or bust graffiti on the side would you look at a twisted up bunch of metal millions and millions of years old and scream spaceship? There are lists and lists of weird things with no explanation out there. I suppose a global civ would leave behind enough evidence for us to speculate on, but one small outpost would probably not leave enough to prove anything.

So, have humans permanently scarred the earth then? Are mineral deposits fixed or in flux? How long before it all gets scrambled again? Plastic is not a thermodynamic sink, it will ultimately decompose to something else with enough pressure and temperature (I read the paper on plastic sedement and was not impressed, classic case of overreaching). 

As for fossils, humans became dominant in the last few millenia, and if you look at mamallian biomass today we make up quite a shocking majority, but what about divided over all the time since mammals arose?

[Laie]

1 hour ago, kerbiloid said:

A native one. Nothing prohibits an advanced guest civilization from building their outposts if they like.

I think there's not a single spot on earth where you wouldn't need some kind of permit (scnr).

More to the point, while the remains of a terran civilization would be all over the place, more localized stuff like a single alien outpost is much easier to miss.

[kerbiloid]

43 minutes ago, PB666 said:

Whose guest, i dont remember inviting any aliens. 

They foresaw your future wish. Of course, you could try to send away their peaceful battleship.

43 minutes ago, PB666 said:

So alien civilizations comes and settles in our late heavy bombardement period, not very smart aliens. 

Why so? That was about the outposts, not about total colonization.

Say, pyramids.
Scientists see an ancient Egyptian building and search historical facts on it.
UFO enthusiasts see an extraterrestrial facility full of unknown abilities, built by a wise civilization wishing to upgrade us up to their own level.
Mystics see a magical artifact, a place of power.

And meanwhile, say,  that's just a shed for a temporary radio relay point, hastily made of local stone rubbsh, with portable field instruments, by a brigade of penalized extraterrestrial lawbreakers, who were sent to this hole of the Universe for correctional labors.
That's why they (pyramids) look so rude, careless and awkward inside. With absurd tilted and small corridor and so on. Just nobody cared.

While their overseer was running there and back, adjusting and confirming blueprints and invoices, bored workers were killing the time, making funny stone sculptures with their superbeam instruments.
Mostly statues of local habitants, sometimes (under after an extraterrestrial tea?) - sphinxes.

When their unit was dismissed, took off the equipment and left those useless piles of stone with strange spaces inside. And statues because they were limited with handy baggage.

Edited July 5, 2016 by kerbiloid

[CSE]

17 hours ago, kerbiloid said:

Of course, no coal or oil, because they would burn them before us.

This. We've depleted fossil fuel deposits in a pattern that's characteristic of how easy they were to access. Even if you had no knowledge of the total amount there was before civilization, you would still be able to see that pattern a hundred million years later. If a previous industrial civilization had existed, a science of petrogeology that didn't take this into account would never have gotten off the ground.

P.S. - Which is why, if we fluff this world up, the civilization after us Will Not Go To Space Today.

Edited July 5, 2016 by CSE

[magnemoe]

10 hours ago, kerbiloid said:

A native one. Nothing prohibits an advanced guest civilization from building their outposts if they like.

True, it would be very hard to detect an research outpost from prehistory time, geological time, way harder

Millions over thousands of years has a larger footprint than 100 in a couple. If we found technological items from prehistoric time I would guess alien origin.

No most of the ancient astronaut stuff is stupid, 1000 year old aluminum items, 100k year old steel change this

[insert_name]

I wonder how many satellites from the first civilization  would last, and what effects they would have on the second one 

[PB666]

1 hour ago, insert_name said:

I wonder how many satellites from the first civilization  would last, and what effects they would have on the second one 

None, four  body problem. They would eventually reach an elliptical orbit that would decay in the atmosphere, collide with orher satillites and the pieces would decay, simply decay, or if in gso would be drawn into a exiting orbit.

[todofwar]

On Monday, July 04, 2016 at 6:02 PM, Bill Phil said:

No. There was a city that was completely destroyed by some ancient power, and we only know if that particular city because of the bureaucracy that the power had. Maybe it wasn't Carthage, but the point still stands.

Pretty sure it was Carthage. But I think there were some remains left over after its destruction. Dan Carlin described ancient warfare as nothing more than a more labor intensive version of modern warfare, we always have obliterated cities, it's just easier to do now. 

Other examples include Assyria and whoever the Mongols didn't like.

[kiwi1960]

In the 1930's, someone found a woman's chain embedded in a rock..... and a miner found a chalice in coal...

There are many other such examples ... a Aztec type pyramid off the coast of Japan... among other things...

Given the age of the planet.... we may not be the first... its as arrogant to say we are..... as it is to say we are alone in the Universe.

 

[Green Baron]

I've found toothpaste and wwII-style ammunition in neandertal-layers. That clearly shows that neandertal had a civilization capable of such production chains and all implications thereof *rolleyes*.

(No offence dear neandertals, you did a great job in the ice age !!)

What seems arrogant to you is a question of education and subsequently of time and effort one spends and dedicates to studying and learning.

 

Edited July 7, 2016 by Green Baron

[kerbiloid]

19 minutes ago, Green Baron said:

I've found toothpaste and wwII-style ammunition in neandertal-layers. That clearly shows that neandertal had a civilization capable of such production chains and all implications thereof *rolleyes*.

If some of these things are American, it also proves their ability to perform an oceanic voyage.

[RenegadeRad]

What do you think illuminati is?

40 minutes ago, kerbiloid said:

If some of these things are American, it also proves their ability to perform an oceanic voyage.

OOOOOH DAAAMN

[wumpus]

On 7/4/2016 at 3:38 PM, DDE said:

Well, we can pretty much exclude another Homo sapiens civilization unless we assume a stupendous degree of cover-up. Conspirologists are prone to imbuing The Man with incredible skill of erasing memories and picking up all the cigarette butts.

As to dinosaurs, it's just doubtful that they in fact could. They seem to have lacked the sheer bio-energetics needed to run the requisite neural machinery. No, we wouldn't find their society, but we aren't seeing any significant evolutionary tendency that could lead to a sentient species; at our current level of insight, we'd expect to see clearer evidence of "sauroprimates".

The real question is if you could miss the required order of "sauroprimates".  My take is that it would be hard enough to find evidence of great apes in 65 million years, let alone the rest of the primates.  Humans have only really exploded across this planet in 10k+ years, so are unlikely to be all that fossilized (and how many cultures build cemeteries in places that fossilize)?

We could miss the effects of technology from 65 million years ago (although a geologist might point out widespread mines that were reasonably shallow back then, suggesting that they never exploited available wealth).  Even the continents from that era are gone.  The only real question is that if we could miss a small offshoot of dinosaurs that had runaway sexual selection for power brains*.  Judging from the upheavals that I've seen in this science since I was a boy playing with dinosaur toys (hint: pretty much everything I learned then was wrong) I'd find it easy to believe we haven't found all species of dinosaur.

Note that this assumes that such a technologically advanced society suddenly dominated the ecology for a very short duration (and thus barely entered the fossil record) and then destroyed itself (presumably the KT layer).  If it was capable of such a widespread disaster, I'd expect some sort of flotsam floating around the solar system (especially if they moved a comet).  I'd go so far as to call it (slowly) falsifieable (discovery** or complete lack of such flotsam).

And yes, there is sufficiently complete observation of the Earth to be aware that no "super high tech" civilization existed (although there may have been those higher tech than the previously suspecting top-banana, vegatiative growth can destroy a lot).  Mining records are also conclusive: there never was a [human] civilization capable of widespread mining/oil-drilling/etc. that we don't know about.

I suppose there could have been such a civilization right *after* the KT event.  But that would require the ancestors of the civilization being in the "lucky few" surviving species (and this would likely require them to be widespread enough to be in the fossil record).  Presumably they would get swallowed up as the new dominant species stabilized.  Such a civilization wouldn't require getting to the point of being capable of destroying itself, the surrounding ecology would likely finish it off.  I just don't think it is at all likely.  It certainly was an era of rapid evolution.

* while not always accepted as how humans evolved, it would at least form the basis for another intelligent species***

** if you think NASA has enough denialists loudly barking around them, imagine what happens if they find a dinosaur-built spacecraft.  Perhaps you could create a meta-hoax "they really found it, but had to cover it up to avoid offending the creationists and other denialists controlling the NASA budget***".

*** enough to question if there has been a single intelligent species on Earth.

 

[todofwar]

10 hours ago, Green Baron said:

I've found toothpaste and wwII-style ammunition in neandertal-layers. That clearly shows that neandertal had a civilization capable of such production chains and all implications thereof *rolleyes*.

(No offence dear neandertals, you did a great job in the ice age !!)

What seems arrogant to you is a question of education and subsequently of time and effort one spends and dedicates to studying and learning.

 

For someone who claims to hate this kind of thread you sure do seem to enjoy reading it.

Interesting point though, since our entire civ will be compressed to a tiny layer in terms of strata, would we even be able to tell anything about our civilization? We'll have the odd bit of fossilized tech here or there, but as an example think about the Antikethera mechanism. I doubt that was the first of it's kind, seems entirely too refined for that, yet I don't think we have a clear "fossil record" for what came before it. So, from the perspective of someone 100 million years from now they'll see pottery, wheel, computer, rocket, all happening seemingly at the same time. There may be a sheet of plastic squeezed in somewhere, and odd deposits of metals, but it's not like archaeology is possible on such a long scale. So, getting back to what this thread was started to discuss, what would be left behind? We don't even know the full extent of ancient Egyptian tech (we have a very good idea, but the point is the record has already started to deteriorate in only 3,000 years)

If every human dies tomorrow, and another civ arises in 150 million years, will they know about us? What will they know? They'll have a ton of fossils probably, will see a great extinction event, and can probably tell we became dominant, but what about technology? And don't forget stubbornness and skepticism play into this, what critical mass of evidence would be required? We find anomalies all the time, but since the weight of evidence tells us neanderthals didn't have toothpaste we find ways to explain them in our own context. So, if you found some odd geological formations, some depleted resources, and a few tiny patches of weird plastics here and there what conclusion would you draw? It took us a long time to figure out we move around the sun, because geocentrism was a good enough theory to account for the odd deviations. This hypothetical future race will have a theory that they were first, and as paleontology develops they will start to find more and more evidence that maybe something else was here first. But their theories will be built on explaining the world without that previous civ existing at all. So, any and all anomolies will first be forced to conform to the prevailing theory, until something breaks. That's how science advances after all. The question is, will we leave enough behind to break their theory? Or will future geologists be hopelessly trying to figure out how polyethylene forms naturally?

[Green Baron]

Your take is mislead and doesn't reflect reality. A civilization 65my ago would have left many clear traces, structural, isotopic, climatic, in fauna and flora, almost everything. You would the traces of infrastructure, large and small buildings, change in plant- and animal-composition. It may be hard for you to realize what geology and palaeontology can do. The remnants of a civilization comparable to ours would be visible averywhere.

And basic assumptions contradict the current state of research:

1.) Humans have spread across the planet since 2.6my, different species, always more than one at a time. Do not assume hunters and gatherers had no impact on the surrounding. This is the case since at least the OIS-3. For older things: i've found the smithsonian site for human evolution (i only know of good German or French publications), maybe that's a start for you guys that rely only on the internet for information gathering (http://humanorigins.si.edu/research/age-humans-evolutionary-perspectives-anthropocene).

2.) Continents are, concerning size and basic distribution, the same than 65my ago, the positions are different. Especially australia/antarctica. See scotese website. It's a false assumption that we don't know the arrangements.

3.) Sedimentary geology is able to deduct mass, energy and direction of deposits from 100s of millions of years ago, together with remnants of flora and fauna, if conditions permit. Areas like southern Germany are investigated thoroughly since 200 years, leaving little gaps (only cretaceous deposits are not there, but they exist elsewhere) from the late permian on. Climate and landscapes where reconstructed quite well. North Americas grand staircase has an even longer record but isn't researched that extensively (but there is nothing that supports your assumptions, not even in area 51 i dare say).

4.) There are no roads, railroads, harbour walls, power plants, dams, mines, bridges, fundaments/bases, groundworks like todays autobahns or fast ailroads, where whole landscapes are reconstructed or any other traces of infrastructure like mining, or deposits that have been artificially moved and don't fit. Do you really assume that wouldn't catch our eyes ? Then you are wrong, i am as sorry as possible.

5.) There are no big brains (in many cases not even brains as we understand them from todays mammals). A civilization, even if present only for a few thousand years, would have spread over the world, leaving traces everywhere and many under favorable conditions. It would be the dominating find in the fossil record. There'd probably be so many that we would exactly know how they looked, what they worked and what they ate.

6.) There are no isotopes from atomic things. Otherwise it would be impossible to date rocks today. There'd be huge spikes and jumps and we'd wonder how samples from the same layer, a few centimeters apart can yield totally different dates, or none at all.
 

I stop now, that's the longest thing i've written here. If you just want to believe then i declare myself helpless.

Edit: forum merged my posts: the above is an answer to @wumpus.

 

47 minutes ago, todofwar said:

For someone who claims to hate this kind of thread you sure do seem to enjoy reading it.

Bloody mess, i don't. I just feel urged to spread some reason and lead people away from fruitless speculation ...

But i did spend to much time in here, that's true. Other things need attention as well. Nothing i wrote is much of a secret or so, everything is published.

 

Edit: i answered your questions.

 

Edited July 7, 2016 by Green Baron

[Scotius]

Bur we've found the "Sauroprimates". Like i wrote earlier, dromaeosaurids - small, agile carnivores general public calls "raptors" were dinosaur with the most advanced, best developed brains. Yet despite belonging to an order of animals evolving for more than 100 millions of years, they barely equalled dogs in terms of intelligence. A Troodont would make a cool pet, but he was far from becoming a civilisation builder. Besides, their upper limbs were suited better towards becoming wings (which eventually happened to birds, which likely evolved from "raptors") than 'arms' with a high range of mobility and precision. No. no way it would happen without leaving a trace in fossil record.

[wumpus]

2 hours ago, Green Baron said:

Your take is mislead and doesn't reflect reality. A civilization 65my ago would have left many clear traces, structural, isotopic, climatic, in fauna and flora, almost everything. You would the traces of infrastructure, large and small buildings, change in plant- and animal-composition. It may be hard for you to realize what geology and palaeontology can do. The remnants of a civilization comparable to ours would be visible averywhere.

And basic assumptions contradict the current state of research:

1.) Humans have spread across the planet since 2.6my, different species, always more than one at a time. Do not assume hunters and gatherers had no impact on the surrounding. This is the case since at least the OIS-3. For older things: i've found the smithsonian site for human evolution (i only know of good German or French publications), maybe that's a start for you guys that rely only on the internet for information gathering (http://humanorigins.si.edu/research/age-humans-evolutionary-perspectives-anthropocene).

2.) Continents are, concerning size and basic distribution, the same than 65my ago, the positions are different. Especially australia/antarctica. See scotese website. It's a false assumption that we don't know the arrangements.

3.) Sedimentary geology is able to deduct mass, energy and direction of deposits from 100s of millions of years ago, together with remnants of flora and fauna, if conditions permit. Areas like southern Germany are investigated thoroughly since 200 years, leaving little gaps (only cretaceous deposits are not there, but they exist elsewhere) from the late permian on. Climate and landscapes where reconstructed quite well. North Americas grand staircase has an even longer record but isn't researched that extensively (but there is nothing that supports your assumptions, not even in area 51 i dare say).

4.) There are no roads, railroads, harbour walls, power plants, dams, mines, bridges, fundaments/bases, groundworks like todays autobahns or fast ailroads, where whole landscapes are reconstructed or any other traces of infrastructure like mining, or deposits that have been artificially moved and don't fit. Do you really assume that wouldn't catch our eyes ? Then you are wrong, i am as sorry as possible.

5.) There are no big brains (in many cases not even brains as we understand them from todays mammals). A civilization, even if present only for a few thousand years, would have spread over the world, leaving traces everywhere and many under favorable conditions. It would be the dominating find in the fossil record. There'd probably be so many that we would exactly know how they looked, what they worked and what they ate.

6.) There are no isotopes from atomic things. Otherwise it would be impossible to date rocks today. There'd be huge spikes and jumps and we'd wonder how samples from the same layer, a few centimeters apart can yield totally different dates, or none at all.
 

I stop now, that's the longest thing i've written here. If you just want to believe then i declare myself helpless.

Edit: forum merged my posts: the above is an answer to @wumpus.

 

Bloody mess, i don't. I just feel urged to spread some reason and lead people away from fruitless speculation ...

But i did spend to much time in here, that's true. Other things need attention as well. Nothing i wrote is much of a secret or so, everything is published.

 

Edit: i answered your questions.

 

[tl:dr - having mining areas reasonably close to the KT line (and dinosaur bones) pretty much kills the idea of a dinosaur civilization.  While you are unlikely to detect a 65 million year mine (not only will the shaft will collapse, but I'd expect the rock to fuse itself together given a few million years), but I wouldn't expect new ore to pop up.  Those "civilized dinosaurs" would presumably mine at least a measurable amount of ore.]

My assumption was that a possible dinosaur civilization rose roughly as fast as our own and caused the KT layer roughly as soon as possible (similar to ourselves nuking humanity to death during the Cold War).

1.  All effects on ecology would be wiped out by the rest of the effects in the KT layer.  I'll have to learn just how long the "dinosaur extinction" actually took, but I'd assume the civilization would immediately collapse.  Being able to determine that sudden changes after the asteroid were caused by a "dinosaur civilization" would be mostly impossible.

2.  This is the biggest problem with a dinosaur civilization.  I was thinking the continents mostly moved by forming new land and subsuming the old, but obviously there exist dinosaur bones on land.  I suppose that any coincidence with low (or smaller) resource deposits coinciding where the KT layer was near ground level would be a published and widely known.

3.  Largely irrelevant.  The average human population for the last 20,000 years has been less than a million.  We just won't show up in the fossil record unless we manage to live for a few more millennia at current rates.  Even our food supplies are unlikely to fossilize unless jello suddenly becomes unpopular.

4.  We can't even be sure of what caused the KT event, how in the world do you think dams, mines, and buildings are going to survive.  If a crater of that size erodes to the point of disappearance, you aren't going to find any roads.

5.  So no birds have brains.  Tell it to the crows.  And the same forces that smoothed over the largest crater in the last hundred million years will leave the tiny evidence of intelligence for us to find.  

6. All the isotope issues will be simply *in* the KT layer for well inside any error of measurement (within a century or so), good luck showing the error on that one.

I'm guessing the existence of usable mines within striking distance of the KT boundry is the only reason to believe that a dinosaur civilization appears impossible.  Even the existence shouldn't be a problem, but there should be a measurable lack of resources with at least a measurably smaller percentage of mines that follows roughly that line (and always seems to disappear below it, no effect on anything above).  The other arguments could easily be covered up assuming they coincided with the KT event or simply disappeared after 65 million years.

I'm fairly sure that a dinosaur civilization couldn't disappear under "natural" conditions.  It either did itself in with the KT event (and such covered up any other evidence they existed) or never existed at all.  The fact that both plentiful mining and dinosaur bones exist in Montana* implies that unless such areas otherwise become inhospitable to the dominant dinosaurs (perhaps a lakebed or something) these dinosaurs didn't cause a technologically-created extinction event.

* That's pretty much the limit of my knowledge of mining and where to find dinosaur bones (my eight-year old self is kicking me right now.  I was *really* into both paleontology and geology).  Anybody know of the overlaps between mining areas and dinosaur bones?

[lajoswinkler]

Materials would be left. Mineral and organic polymers.

 

Radioisotopes would be left.

 

So, nope. We're the first ones.

[micr0wave]

i wonder .. isn't there a theory that the moon was the result of a collision of a mars sized planet with the 'proto-earth'.

What if that proto-earth had a civilization ? Could there be traces be found ?

[todofwar]

1 hour ago, micr0wave said:

i wonder .. isn't there a theory that the moon was the result of a collision of a mars sized planet with the 'proto-earth'.

What if that proto-earth had a civilization ? Could there be traces be found ?

I always thought that happened before the earth was capable of sustaining life, but if not I imagine that kind of impact would wipe any evidence out. 

Not relates to the quote above but this would get merged anyway. People keep asserting we leave behind enough evidence, but would it reach a critical mass? Again, any species that evolves would treat everything they find as natural formations. Anything useful they find will get mined and reused. Plastics would be burned as a useful fuel. So, at a certain point our left overs will stop being a complete record. And as @wumpus said, our civilization will be compressed geologically speaking such that you won't be able to tell the modern era apart from the neolithic era. So, if a civ grows under the assumption that they were first, they will decide all these odd fossilized bits of tech must be natural. They may not even find much depending on how long after us they come. Will there be a critical mass of evidence to overturn their belief they are first? I think if we found plastic sediment in the jurassic layers we would begin trying to figure out how it formed naturally, and probably wouldn't say it's the result of a distant species. And I don't think we've depleted enough resources yet for that to be noticeable until such a civ maps the earth completely and sees a pattern, something we have not done yet. 

Tldr: it's not just about the evidence, it's a question of how much evidence is necessary to force a civilization to change its mind about being first, considering their world view would presume every odd feature they see is natural including plastic and isotope patterns.

[RainDreamer]

It would require us to have better understanding of planets formation to see what is natural and what is not. 

Also perhaps there was a civilization that completely dependent on bio tech, their artifacts would look almost natural to us. Or maybe we *are* the artifacts. 

* dramatic music*

In any case though, if there was a civilization advanced enough to send stuff to space, we might see some of that already.

[RocketSquid]

If there was a civilization, they were either very, very, very old or didn't use fossil fuels, plastics, or large amounts of metals. Occam's razor says no.