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I am inspired by Dr. Robert Schoc's hypothesis that the Great Pyramid and Sphinx date back to a lost civilization from 10,000 BCE.

The Question:

Suppose an asteroid/mega solar flare/etc. reduced today's humans back to a hunter-gatherer state; but after 10,000 years humans have again achieved the technology level we have today. Would archeologists of that time be able to tell that something more than hunter-gatherers existed before them, and would they be able to tell how advanced we were?

(I'm not sure if I want structures such as Mt. Rushmore destroyed or not. I would think such structures couldn't be made by hunter-gatherers, but I don't know)

If yes, at what point in history would we have had to be wiped out so that there would be no trace of us after 10,000 years?

My Thoughts

I think future archeologists may find our nuclear waste deposits. However, I don't know what shape they would be in after 10,000 years or if they would be recognizable as man-made.

I don't think anything else would survive, so I would say the historic cutoff would be when we first started having nuclear waste deposits.

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    $\begingroup$ Possible duplicate of What would be left of a civilization founded in dinosaur times? $\endgroup$ – o.m. Jun 10 '18 at 6:13
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    $\begingroup$ If future archaeologists have spaceflight, they will be able to find the identifiable remains of the Apollo missions 250 million years from now. Apollo could conceivably outlast several different civilizations over it's quarter billion year lifespan...... $\endgroup$ – Thucydides Jun 10 '18 at 12:57
  • $\begingroup$ We will never be knocked back to a Hunter-Gatherer state because knowledge does not perish due to a solar flare. Books will survive, books on chemistry, medicine, maths, physics, astronomy, molecular biology, computing, philosophy, human rights, economics, democracy... plus we still have the seeds, animals and farmland needed to sustain us without resorting to Hunting/Gathering. $\endgroup$ – MichaelK Jan 15 at 15:45
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Absolutely.

The largest traces would be cities (it takes a lot to wipe out even a prehistoric settlement, and there's no way all modern cities could be thoroughly covered in sand).

Then, mines: there are mining operations that extend for kilometers, and you're not going to "lose" one in ten thousand years unless you employ several decent-sized asteroid strikes.

The Udachanyay mine

Any new civilization would require mineral resources, and would find most ore deposits to have already been mined out. They'd also find large landfills here and there, with lots of refined minerals, plastics and so on.

Moreover, this would conclusively demonstrate that the previous civilization was pretty advanced: not only several special steels and alloys will easily last ten thousand years, but a less advanced civilization could never have produced such traces.

And of course pollution. We can pretty well map out atmospheric composition for the last 30,000 years and more in the Antarctic ice cores. There are several distinctive layers of soot there now (which actually defeat the purpose).

Finally, radioactive traces. There's no reason why Schloch's alleged civilization should have produced them, but we did, and artificial isotopes such as technetium 99 are likely to outlive humanity. As soon as we started worrying about radionuclides and developed tests for them, we were able to map their relative abundance. There is no way we could have missed a 99Tc spike later than one million years ago, and there is no natural process that produces 99Tc (unlike 14C, which could be explained by a GRB, nasty solar flare, or alteration in the cosmic environment).

At what point in history would we have had to be wiped out so that there would be no trace of us after 10,000 years?

Around 20,000-30,000 BCE. After that date, we begin having reliable fossil evidence that made it to our era, two hundred centuries later. It follows that if someone wiped out the Altamira tribe, we would still find their paintings - unless the "wiping out" also included obliteration.

In that case it would depend on the obliterating technique. Still, I don't think you can get much later than 5,000 BCE at most.

Cultural Memory

While it is possible that stories about a Golden Age where man could fly, go to the Moon and watch Youporn would be dismissed as fantasy and myth, it is possible for such a memory to disappear completely.

It would take a lot, but there's something called damnatio memoriae - "damning of the memory". Imagine that the shock of the wipeout spurred a new religion - one where technology and the "old way of doing things" was blamed for God's wrath. The new Church "hierarchy" fixes very few proto-technological "tells" that are used to recognize anathema - "Thou shalt not make signs that convey meaning, unless larger than a man" or "Thou shalt not make use of anything that has been touched by fire, except for food".

Something of that kind appears in David Weber's Empire from the Ashes (the planet Pardal is inhabited by humans that have forsworn technology and succeeded in forgetting everything about their having been members of the Fourth Empire), as well as in the Safehold series of the same author. There are also several other stories (e.g. Wyndham's The Wheel, Startling Stories, January 1952).

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I'd be optimistic in a sense. There is no way to reduce humanity to the Stone Age as long as enough educated adults remain. Look at the Leonardo da Vinci level of tech. All you need for it is a basic engineering knowledge (widely available in 21st century) and wood. As wiping out everyone but babies while making them survive is not an option, you'd need something more than a nuclear war to let humanity survive, but forget its knowledge. A flebtonium-based memory wipe, maybe?

Next, the question is what of humanity remains. If all humans would disappear, future archeologists would find enough evidence of our existence. Probably even more if it survived. Rich men's waste dump is poor man's metal ore. In some kind of an post-apocalyptic stetting, people would scavenge waste pits and abandoned cities for materials.

So, in most cases, badly reachable, but durable artefacts of older civilisation would remain. Humanity would rather degrade not to the Stone Age, but to Enlightenment, augmented by extended medicine and engineering knowledge, as well as more advanced materials from the remains of the previous civilisation.

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    $\begingroup$ "There is no way to reduce humanity to the Stone Age as long as enough educated adults remain." +1 In fact, realistically, it's impossible to reduce humanity to the stone age without some outside "force" (godlike beings forcing humans to not use their intelligence... for example) keeping us from using what we know. The number of humans today who could be "knocked back" to the stone age number much, much less than 1% of the world population, thus... impossible. It's a common idea on the site, though. $\endgroup$ – JBH Jun 9 '18 at 17:17
  • $\begingroup$ Educated adults will have knowledge after an apocalypse, but if they don't have resources to apply that knowledge to in time it will not be taught to future generations and thus lost. $\endgroup$ – Loren Pechtel Jun 11 '18 at 4:53
  • $\begingroup$ @LorenPechtel - even with all that education lost, stone age is a bit...unrealistic. Honestly, most of the stone age technologies are very rare nowadays (techniques, comparative properties, locations), especially as compared to something like hobby blacksmithing, and there are a number of fairly widespread skills where knowing something is possible will make a big difference, even if the how is lost. $\endgroup$ – Megha Jun 13 '18 at 4:40
  • $\begingroup$ @Megha The reason for stone age is that you can simply pick up the tools for early stone age. Anything later than that requires skills they probably don't have and in general resources they won't be able to get (the easy-to-obtain resources were already gathered long ago.) $\endgroup$ – Loren Pechtel Jun 13 '18 at 20:08
  • $\begingroup$ @LorenPechtel - I think you're underestimating how complex stone technologies are, and the possibilities of scavenge. Copper (pipes everywhere) can be worked with a bonfire, a reed or pipe for air, and a stone - there's your knife or arrowhead - I'd a friend make such in his backyard with no other info. To make the same from stone, takes knowing what kind of rocks fracture correctly, how to find fracture points, what kinds of materials for tools, safety while making, how to attach a handle ... I took a flintknapping class, it is fun but not easy. $\endgroup$ – Megha Jun 13 '18 at 23:21
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A lot of what we do today sinply will not decay in less than 10,000 years. As other have mentioned plastic would be a proof of a civilization having existed. Other things would also last more than that... A complete exhaustive list would probably fill a book, but here is what' on the top of my mind:

  • Jewelry. Gold, silver and platinum are quite tenacious, chemically speaking. So is quartz, as well as many types of rock used in jewelry.
  • For the very same reason, gold plated teeh would also be a good indicator of a civilization. No known irrational animals adorn their teeth with gold.
  • Electronic circuits. While many of the things on a motherboard would decay in ten millenia, the silicon in its parts would not - it is as chemically stable as sand for all practical purposes. Many circuits and wires also have gold in them.
  • Satellites. Unless your doomsday scenario involves taking down all satellites, or removing them from the solar system, they would be a strong indicator of a previous civilization - even if they are depowered or otherwise rendered permanently non-operational. I know their orbits decay with time, but some satellites are expected to still be there more than eight million years from now. Side note: I think removing all traces of satellites from the solar system would require orders of magnitude more energy and technical sofistication than what is required to wipe out all traces of civilization within the atmosphere.
  • Actual time capsules. We as a species have a habit of making time capsules, and they might last more than 10,000 years.
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  • $\begingroup$ Glass. So common people tend to overlook it. Chemically stable, and found in everything from large sheets to containers to solid decorations and objects or assorted sizes, colours, and compositions. $\endgroup$ – Keith Morrison Jan 15 at 16:50
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Processed materials. Composites, plastics, alloys, even ceramics don't occur in nature. No matter how badly degraded the objects using them get, many of these underlying materials will survive in some form, be it chips, shards, or even dust, for extremely long periods of time. Many plastics, for instance, are not attacked by biological decay, don't oxidize, and their shards can survive most plausible types of physical mistreatment. Aside from the small proportion of artifacts unlucky enough to encounter lava, their remains would survive as a clear indication of a technological society. But you don't need to be that sophisticated - even something as simple as bronze, in whatever form, is a strong indicator towards active metallurgy.

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    $\begingroup$ The layer of plastic in the archaeological record will be tough to miss. $\endgroup$ – arp Jun 10 '18 at 0:11
  • $\begingroup$ I thought plastic lasts only hundreds of years $\endgroup$ – Ovi Jun 10 '18 at 0:50
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    $\begingroup$ @Ovi Plastic objects do have a shelf life; they'll get brittle and crumble. But the shards and dust that result will last a lot longer, and are chemically very distinct from materials found in nature. Plus you'd always have freak preservations, like of ancient pottery. $\endgroup$ – Cadence Jun 10 '18 at 1:29
  • $\begingroup$ I was thinking of the often quoted figures such as "plastic bags take 50 years to decompose". Though I don't know what "decompose" means $\endgroup$ – Ovi Jun 10 '18 at 2:08
  • $\begingroup$ @Ovi There are different kinds of plastic, of course, which break up at different rates; I was envisioning a harder plastic like you might see work buckets made out of, for instance.. As for what "decomposition" means in this context, it's a bit ambiguous. Plastics are made of very long, repeating chains of molecules; decomposition could mean those molecules are changed, or just broken apart (I would expect the latter would happen first). Sort of like picking apart a cotton ball; what you're left with is "broken down" but it's still clearly cotton. $\endgroup$ – Cadence Jun 10 '18 at 2:18
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There's been a brief History channel series, Life After People, that explored this question in thorough detail. It's far more visual than an answer can be, and each episode ends in a 5K-10K year prediction.

Most of our cities will be covered with soil, but some of the Northern-most ones could survive as piles of rubble with almost no cover. It depends almost entirely on new soil deposition rate. Still, even Angkor Wat, which is in the tropics, hasn't been buried much, and will remain identifiable for millennia.

The humanity would have to be removed around 2,700 BCE to remove immediately obvious, unmistakable traces that even a cursory visual scan from space would pick up. To leave no traces at all, pretty much to before cave paintings (over 70K years).

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10,000 years are not enough to wipe out...skip that, ERADICATE a global civilization down to the ROOTS. Unless these archaeologists were unlucky enough to search only in Antarctica or in the Death Valley et similar places, traces of our existence are everywhere.

You'd need tens of thousand of years, if not millions, for geological and climatic processes to cover everything under a nice layer of rock. And even then, paleontologists would find us. Just as we found dinosaurs.

So, no, even after our demise we'd survive history.

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There would be traces. Just as there are traces of past civilizations now. A million years would make it all very hard to decipher. Plastic and Nuclear waste being the last trace elements of our man made mess. The faces on Mt Rushmore and some Dams and Levees? Machu Picchu? Pyramids? Bones? Satellites?

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