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Behaviourally modern humans showed up around 50000 years ago, but what we can call a civilization: settlements bigger than a few huts, agriculture and complex social structure, started only some 6000, maybe 8000 years ago. Even if we want to push it, the earliest signs of the Neolithic Revolution come from 12000 years ago.

It means that there is a lot of time when a civilization might develop and then vanish without trace. But how?

My question is: If there was a considerably big civilization - ie. at least a few cities, big field of corn to sustain the population, some big monuments, etc. - what disasters could destroy it so thoroughly that we are not able to find any traces of it with our modern archeological equipment?

EDIT: Reworded to narrow the subject.

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    $\begingroup$ First off, I think the timelines you give are more than a little off. There is evidence of human civilizations from far longer ago than 8000 years. Second, at that point in time most of Europe was covered in 2 km of ice, which, when it melted, flooded many areas, and wiped much evidence away (the Black Sea - which was not covered by ice - used to be a plain). Third, you're failing to consider just how difficult it is to preserve anything over that length of time. Archaeologists have found tools dated to almost 70 000 years ago, but how rare is such a find? What are the chances? $\endgroup$ – AndreiROM Feb 5 '16 at 13:36
  • $\begingroup$ I'm interested in something more than a small settlement. I know about Jericho and a few other settlements from around 10000 years ago, but I think about something bigger, like ancient cities of Egypt and Sumer. Ruins big enough that something extraordinary would have to happen to hide it completely from our sight. $\endgroup$ – makingthematrix Feb 5 '16 at 13:51
  • $\begingroup$ Consider that Antarctica was once not covered by ice. It's entirely possible that if the Earth's crust were to shift again and that continent was once again revealed to us we would find some rather interesting things. Look at most Roman and Greek ruins from only 2000 years ago - most are decayed to the point where they're collapsing even as we try to maintain them. Throw in another 50 000 years of Mother Nature taking her best shots at them, and what would remain to even indicate that those civilizations had ever existed? $\endgroup$ – AndreiROM Feb 5 '16 at 13:55
  • $\begingroup$ Of course, but in the same time people would rebuild everything for hundreds of times, maintaining and spreading their civilization. The idea about Antarctica is a good one as there is no escape from glaciers and eventually everything would be buried under the ice. But in other places some other disasters would be necessary, not just a slow decay. $\endgroup$ – makingthematrix Feb 5 '16 at 14:04
  • $\begingroup$ Take into consideration that changing climates / natural disasters also drive people away from certain locations. If a place is abandoned for long enough it can be buried and forgotten before anyone comes back to rebuild (the jungle cities, for example). Also, the human population long ago was much, much smaller than it was even 2000 years ago. $\endgroup$ – AndreiROM Feb 5 '16 at 14:21
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You mean the one buried under the ice caps of Antarctica?

Given that we're still discovering the remains of ancient cities thanks to satellite photos, I'd say the answer to your first question is "fairly big".

To try to narrow down the size a bit, I refer to this article about ancient cities in the Amazon. Many civilizations existed and have been identified in the Amazon floodplains, but the less fertile uplands where thought to be empty. Recently discovered remains hint at a population size of 60,000 people, rather than 0.

It took us until this century to find (part of) a civilization of 60k people in a remote jungle-like location. I'd say that is a good starting point. You might get away with a greater size if the location is more remote or covered by plants/mud/ice/etc. The closer the site is to our current civilization (especially construction work and agriculture), the quicker it will be discovered, so that makes your possible population size much smaller.

The options for city-wiping disasters are fairly limited, so let me try to list them:

  1. Volcanic eruption covering the city in lava and ash. Very effective in burying evidence, but it would have to be huge to cover multiple cities.
  2. Catastrophic flood. Even without divine wrath these can ruin your day. Civilizations located entirely within one valley would be vulnerable to this. An avalanche at the valley's mouth might turn the entire valley into a lake, forcing the inhabitants to abandon all their advanced construction. A natural (or man-made!) dam collapsing at the head of the valley might instantly bury the civilization in mud.

Note that a tsunami definitely could wipe out a coastal civilization, but the remains would likely be discovered easily, because humans have followed coastlines while exploring since the first ones decided they "needed some space to think".

  1. Ice age. The advancing ice would have forced the civilization to go nomadic or extinct. If they were located on Antartica, they might have gotten trapped there or died on the journey to other lands. A handful might have reached Australia, South America or various islands.

Finally, the civilization might existed in a jungle or on floodplains and have died out because of disease or famine, after which nature would have covered it up fairly quickly by either one of the disasters above or gradual processes such as seasonal flooding or plant growth.

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  • $\begingroup$ I like the idea about a valley and collapsing dams. If there was a huge earthquake avalanches and a flood would bury everything. I thought about ice age and glaciers but I think it would be too slow. People with technology just a bit more advanced than that of savages surrounding them would probably just decide to move south and wage war if necessary to break through. They would settle in a more habitable region and we would be able to discover the ruins of that later settlement. But it still a good idea for a story. Thanks :) $\endgroup$ – makingthematrix Feb 5 '16 at 13:43
  • $\begingroup$ ... although, if it was Antarctica, then maybe they wouldn't have a place to go. Good point. $\endgroup$ – makingthematrix Feb 5 '16 at 13:44
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The question really comes down to what would eradicate the signs of a civilisation that existed in this period.

A big one is the sea - people tend to live in coastal regions ( look where most of the world's major cities are now ) and the sea level has risen at least 120 metres since the last glacial period. One could have a considerable coastal civilisation existing at that time but you would need to be looking for it very hard to find any evidence of it now and the sea floor is not currently being mapped with this in mind. This is probably the best candidate.

There are seas that exist now but did not exist relatively recently and that certainly eradicated human living spaces - Doggerland is most local to where I live, but the Black Sea probably flooded within human memory and the Mediterranean only a little before we arrived.

Another big one is ice. Glaciers move slow but they scrape everything back to bare rock and then they scrape the rock away too. It would be very hard to recognise the remains of a civilisation in an area that was heavily glaciated.

For a very enjoyable literary exploration of these ideas I recommend Michael Scott Rohan's Winter Of The World books.

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You'd be amazed what geophysics can pick up

It consists of what appear to be 10 post holes, forming two irregular pentagons which may be the remains of two huts. Thirty stone tools were also found scattered around the site.

"If this is correctly dated and correctly interpreted, it is the first good evidence from 500,000 years ago of a hut structure made by these people."

Now that's two huts, the only trace of which is 10 post holes, not even any structure, just where the holes where the posts used to be.

The only way to obfuscate this sort of thing is for it to be a region that's been continuously occupied since that point. Once the ground has been dug over again the traces are lost forever.


For the second part of your question, it depends on the permanence of the settlement. "Just about anything" is the short answer, small tribes in low population density pick up and move on easily but famine would be the most common city killer.

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  • $\begingroup$ "The only way to obfuscate this sort of thing is for it to be a region that's been continuously occupied since that point. Once the ground has been dug over again the traces are lost forever." - hidden in plain sight. I like it :) $\endgroup$ – makingthematrix Feb 5 '16 at 13:52
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For a fictional scenario, assume that there is a "conspiracy" to hide it.

I'm not talking about centuries-old secret societies with grand masters and secret handshakes who nevertheless put their sigil onto every dollar bill.

I'm talking about a bunch of people, scientists and those who control the research funds, who decided that for political reasons certain lines of inquiry are not acceptable while others are.

  • Consider the Kennewick Man controversy and similar cases. Detailed examination of the evidence might put political correctness in trouble.
  • There were bitter feuds between Greece and the (former Yugoslav Republic of) Macedonia about the "ownership" of the name Macedonia. Both sides were concerned that the use of the name (or the surrender of the name) would imply territorial claims.
  • The belief in the literal truth of the bible would affect how people see relics from the holy land.

Just assume that someone has an interest to twist the facts. Anybody who insists that there is something to the mysterious bricks in the ground is "obviously" a crackpot who wants to tarnish the glorious heritage/manifest destiny of the culture who live there now.

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