Hacker News new | past | comments | ask | show | jobs | submit login
Would it be possible to detect an industrial civilization in geological record? (arxiv.org)
156 points by notional 29 days ago | hide | past | favorite | 178 comments

One of my favorite quotes from Iain M. banks’ Culture series, paraphrased here since I don’t recall which book it’s in, is that technological progress is more like scaling a rock face than climbing a ladder. There is so much room for surprise and incomprehension.

I sometimes think about how vast the parameter space of our physical universe is, and if that vastness means we wouldn’t be able to recognize ancient advanced technology if it’s far enough outside of our current mode of progress.

My favorite example is handing an SD card with all of Wikipedia and the Gutenberg Project and maybe even the Wayback Machine on it to a Roman emperor. He’d look at it and might have a mild interest in the geometrical metal bits on an otherwise insignificant tiny flake of weird material. If the deliverer were to tell him that it contained millions of documents, he wouldn’t believe it.

An expert in the field of storage media could, if for some reason permitted, spend years trying to explain it to the scholars of the time. Even if the expert succeeded in convincing them, it would take an unimaginable effort lasting lifetimes to ever make use of the thing. It would not succeed. Not because those people were stupid, but because the specialization that’s needed to understand the artifact is so far away from from their cultural knowledge and capabilities as to be unreachable. Why should we expect our culture be any different?

The primary counter-argument to this is math and physics, and it’s a pretty strong one. It holds up quite well when dealing with past civilizations that are beneath or somewhere close to our current level of understanding. If you’ll permit another flight of fancy though, imagine an ancient society that figured out how to encode information in the irregularities of crystalline structures: every lame-ass quartz medallion we’ve unearthed could be the equivalent of a 10TB hard drive, and we’d never be the wiser.

I think this is pretty unlikely, but it’s good to be humble and interrogate your assumptions.

My favourite example came from my 9th grade physics class, our textbook told a story that attempted to teach scientific method. Imagine a soda vending machine. Now imagine that I tell you that when you insert money and press the buttons, small goblins are can see what buttons are being pressed, take the money and it put it in a box, and then hand you the selected soda. The textbook even had helpful diagrams that seemed plausible (presuming you had such creatures). Now tell me why this is or isn't so ... and prove it even! How many of you have ever opened up or observed a vending machine (well, on HN I bet that number is surpassingly high, but presume you haven't). It was fantastic exercise in intellectual humility.

For your SD Card example though, I'll nitpick. Sure, just a card and explanation won't get you very far ... but I think something like an iPad (with a good power-supply) would produce enough evidence to convince them (depending upon the individual, I grant there might be some who just attributed it to supernatural forces even in the face evidence and explanation). I suspect humans in general are more willing to deal with "blackbox" technology that has practical application than most tinker types on HN would admit. Very little historical technology that was hard earned with trail-and-error has a theoretical basis known to even skilled practitioners. Even today, to most most people I know, the technology they use on a daily might as well be magic. Sure they know there some kind of "science" beyond it, but I'm also not sure they could convince me it wasn't just goblins if I demanded some theory of it worked.

I mean, one of the first major papers about supercapacitors from back in the late 50s, early 60s, something around that, included a line like "we don't know what's actually going on inside this component when we use it this way, but it sure does store a lot of energy, here's how to make one".

There's nothing shocking or unreasonable or even old-fashioned about understanding what something does before we wonder why it does it. In fact, I'm pretty sure the origin of almost all human knowledge has been precisely in questions of exactly that sort.

Thermodynamics was largely invented to understand how steam engines work.

Last time i checked high temperature superconductors were not understood as well.

One of my favorite quotes from Iain M. banks’ Culture series

Its from "Matter"

Hippense cleared his throat and said, "The type of progress you guys are used to doesn't scale into this sort of civilisational level; societies progress until they Sublime - god-like retirement, if you will - and then others start again, finding their own way up the tech-face. But it is a tech-face, not a tech-ladder; there are a variety of routes to the top and any two civs who've achieved the summit might well have discovered quite different abilities en route. Ways of keeping technology viable over indefinite periods of time are known to have existed aeons ago, and just because something's ancient doesn't mean its inferior."

As far as we know, quasars could be fully artificial, and around them you could find some of our future friends.

and those things would be pretty outdated - ancient - technology by time we spotted them.

Why do you think that an old civilization with deeply held beliefs of gods, magic, seers, oracles ... etc find it hard to believe that a library worth of books has been shrunk down. There is only a small window where magic/gods was being supplanted by monotheistic dogma that is plausible. On the other hand you tell me this dot contains the total sum of knowledge and I’d be nice ... or a drop of this liquid would destroy a solar system I’d be where is the lid

What people profess to believe in and how they act are two different things.

There’s a huge difference between belief in an artifact as holding magical powers and the expectation that you could make practical use of it.

I might be wrong about the emperor’s belief. I chose an SD card particularly because it looks insignificant. Getting an emperor to say “this is a sacred relic” is still a long way off from getting an emperor to say “let us endeavor to unlock the secrets of this relic.”

What would persuade them? It would be really hard to explain how it would be possible.

Yes, over geologic time, nearly anything has no chance of survival. And, yes, the lifetime of such a civilization may be a window that is, geologically, basically invisible.

But an industrial civilization makes a LOT of stuff, and much of that is quite durable and easily recognizable as artificial, and is likely to be scattered all over the planet.

Given that there are places that preserve tracks over 300 million years old, and fossils, well, up to 4 billion years old, I have a hard time imagining that a worldwide civilization that's producing and using aluminum and titanium and ceramics and all sorts of other stuff on a wide basis would not leave something recognizable in basically all the available fossilizing environments. We might not ever find fossils of the species, but are we really not going to find anything from the million refuse dumps and cities and industrial facilities and whatnot, or millions of miles of roads, or the multi-billions of accidental losses bound to be all over the world?

Not to mention objects in high orbit or on the lunar surface, which is a whole other thing.

You have to posit a really limited civilization before I believe it.

The paper addresses this objection in section 1.3: “That this paper’s title question is worth posing is a function of the incompleteness of the geological record … The oldest extant large-scale surface is in the Negev Desert and is ~1.8 Ma old. However, pre-Quaternary land-evidence is far sparser, existing mainly in exposed sections, drilling and mining operations. In the ocean sediments, due to the recycling of ocean crust, there only exists sediment evidence for periods that post-date the Jurassic (~170 Ma).”

that is disingenuous... and is just word playing with definitions.

Most mountains in Europe have surfaced with the last 10-20 mill years, and they have turned earth around to the point that you routinetly find marine fossis in top of 2000m mountains.

If any civilization was around, it would have left a mark somewhere, and mountains would be a great place to spot them.

BTW: According to most scientists, the oldest mountain range on Earth is called the Barberton Greenstone Belt and is found in South Africa. It's estimated that the range is at least 3.2 billion (yes, billion!) years old.

I was also surprised by the statement that the oldest extant large-scale surface is ~1.8 Ma old. There is a citation provided for this [1]. It seems the point is that older features like mountain ranges are subject to significant erosion (as you point out, a marine environment can become alpine during the life of a mountain range) and that this could destroy or disperse most evidence of an industrial civilisation that lives for only a few centuries. The oldest surface which preserves archaeological evidence, due to its low rate of erosion, is merely in the millions of years, whereas what we know about earlier periods is extrapolated from a tiny sample of exposed sections of the earth’s crust. Meanwhile, the seabed is recycled on the 100 Ma scale, and eukaryotic life has been around for 2 Ga. That is a lot of recycling.

[1] http://geomorphology.sese.asu.edu/Papers/Matmon%20et%20al.%2...

It wouldn't take a complex material to recognize a previous civilization. Their civil engineering activities would give them away completely.

Archaeologists can read worked surfaces with amazing skill. E.g. a bed of pebbles could be a lake bed, a road surface, a floor inside a building, a foundation, and there's ways to distinguish them.

Unless the soil was erased/reformed completely there would be a record of almost any activity, from digging a post hole or trench, to building a wall then removing it again then dumping construction waste into the hole then plowing it under. All are different from 'native' soils deposited by random processes.

Geologic time is not enough to erase evidence of worked soils. Not unless it gets scrubbed to the bedrock and redeposited. And even if that happened some places, it wouldn't happen every place. And its fair to say today, that our civilization has been pretty much every place.

Geologic time is certainly enough to erase evidence of worked soils. It spans billions of years, the destruction and formation of continents, and multiple global mass extinctions. Archaeology concerns only the last few million years of hominid activity.

How will asphalt and concrete appear in the geological record? Would it not be identifiable? If we can recognize fossilized bones, a future civilization should civilisation able to recognize concrete with steel rebar inside, no?

Abandoned asphalt roads quickly return to nature. I remember some disused highways near me that were flaking and crumbling away after only 30 years. So bad that you'd have to walk your bike on them.

As for rebar, if any water were to get in there repeatedly it would all just rust away.

The specifics of the environment play huge here. Anything in a freeze-thaw cycle would get obliterated. Dry and cool areas would do better, but then only for so long. Maybe if things were intentionally buried in anoxic environments, like many fossils, you'd have a chance at retrieval.

About the rebar, yes it would oxidise and rust but would it not then react with the surrounding concrete and leave traces, "patterns" behind? Become a special type of mineral, just like so many other minerals that have categorization and names, etc.

It's called hematite and its very widespread. Also, rust reacts with concrete as is, though not as much as with water. Hence why you'll see rebar in those plastic sheaths sometimes. My SO does a lot of work with concrete and these effects are well studied. Turns out that concrete isn't super stable over kiloyear times, let along megayear times. I think you'd have a really hard time trying to conclusively say that some bit of rock was fabricated 10k+ years ago, as compared to all the other types of rocks out there.



Returning to nature is relative. The presence of long-chain petrochemicals in layers where they don't belong, would last for millions of years. And is evidence of that asphalt road.

Yeah, but you'd only see that in sedimenting areas there were uplifted and then weathered; like orogenized river deltas. After that, you'd need to have a lot of samples in the sediment so that there'd be enough exposed rock to care to look at all. Then you'd need enough sample in the rock to detect above background noise. Then you'd need to conclusively explain away any natural causes for the presence of the asphalt, which is naturally occurring anyway.

I'm not saying it's impossible, but it would take a lot of luck.

Yes but considering the total length of paved roads in the world, often using asphalt, how they stretch terrain from coast to coast, on all inhabited continents, that some of it will pass areas that will be uplifted and brought to daylight - I see it as inevitable. It might need a trained eye to see, but it would be there.

Maybe. The surface area of all the roads in the US is ~25k mi2. Which is ~0.6% of the surface area of the whole US. And the US is a pretty advanced country in terms of road density and variety. I think we can say that the total global road density is likely less than even that. Now sure, road density isn't randomly distributed across the surface of the Earth. But future people will still need to get lucky just to see roads at all.

billions of years are certainly present in current geologic history, including ancient soils.

Yeah but I bet there's, even now, like 80-90% (guess) of the planet that don't have a single manmade object on them.

And those million/billion years tracts of land that archaeologists see are like 0.0000001% (guess) of the total. Odds seem good that surviving rocks came from very boring, very pointless places.

It more convincing to look at it the other way.

It's not what such civilizations would have left, but what they would have taken.

Our early civilizations found easily accessible deposits or tin, copper, gold, etc that would have been depleted if another advanced civilization had existed in the past 10 million years or so.

Tin was actually very hard to find. Which is a huge problem for civilizations that wanted to be a part of the Bronze age. Most of the tin used in Europe and western Asia was mined from just a few places in England, France, and Spain. if you find an Assyrian weapon from the 12th century BC in northern Iraq, it shouldn't surprise you if you find it was forged with tin mined in Cornwall.

IIRC tin was one of main motivating factors for the Roman invasion of Britain

Oil, especially, would probably be less common if there was an ancient industrial civilization.

If there was one involving humans, sure. Involving dinosaurs (or earlier)? No. Oil is constantly reforming and the oil we drill today wouldn't have formed back then. Sure, we suck it up a LOT faster than the replenish rate or the rate of natural reintroduction of fossilized carbohydrates into the circulation, but over geological timespans oil has a best-before date. Eventually there will be fissures (due to land movement or erosion) and it would end up being released onto the surface in one way or another.

"Depleted" in this case would just mean mined, transported, and made into something. It doesn't seem farfetched to imagine that, say, an electronics factory would be reduced to an easily accessible deposit of copper or gold in a few million years.

It depends how long the civilization is around. A lot of metal could end up impractical to mine. You can recycle metals, but little chips are being lost to wear and corrosion over time. We're slowly spreading small amounts everywhere.

Some of that would be theoretically be recoverable with a lot of effort and energy, but some of it will basically be gone. No one is going to get back small bits of metal fallen off ships into the deep ocean.

> Our early civilizations found easily accessible deposits or tin, copper, gold, etc that would have been depleted if another advanced civilization had existed in the past 10 million years or so.

Perhaps they also found remains of other advanced civilizations and axploited those?

10 million years is nothing in geological terms.

There have been many civilizations on Earth, maybe not many were industrial (ancient Egypt was clearly semi-industrial so far as lithic tooling is concerned.)

We haven't looked deep enough very much. Many of the 10-25,000 year sites are buried dozens of feet underground. If there are any previous ruins, they're probably a hundred-or-more feet down. Seaside ruins from 10k+ years ago are now under 400 feet of water and 10k+ years of sediment. We've just started to notice evidence of major changes only 13k years back ... with more on the way.

Over 100,000 years, water has scoured (and deeply buried) much of the surface. Consider the number of glaciations in the past 2M years ... each one of which has scoured the surface in northern regions repeatedly. Much farther back than that, and most geo- and bio-records are erased.

The planet's dynamics would have scrubbed almost anything before 10 million years ago. There've been 400 of those; 5 major extinctions left some traces. The scale of upheavals has been massive. How long ago did the Andes arise? It was first noticed in the 1700s that Whole sections of the Earth's surface have gone missing. https://en.wikipedia.org/wiki/Hutton%27s_Unconformity

ok... i get your point, but the major counterpoint:

as earth / plate tectonic move around, underneath earth is constantly surfaced... from dinosaur fragments, to Cambrian era mollusks found in top of mountains (due to earth's crust movement).

If there was a previous 'intelligent' civilization previous to us, they would have altered their environment to be detectable to us even today.

OK then let's find it. We're not really looking. Maybe it is indeed detectable, and maybe it will be hard. Maybe it's already staring us in the face, and our ideas about it are -wrong-.

We -believed- the Clovis story. Until some people -looked harder-. Plate tectonics ... laughed at. Until some people -looked harder-. Absence of evidence is not evidence of absence.

Exactly. Mullusks. Think of them like ants. Almost exclusively small dinosaurs. Things that would have been everywhere, including many places civilization would never choose to go. They are things that would be much more widespread than gameboys (just giving an example).

I’m never sure whether to trust arXiv papers outside my field, so I checked and found that the paper was published in the International Journal of Astrobiology, and the PDF is open access: https://www.cambridge.org/core/journals/international-journa...

The oldest hard-rock mountains are 1.5 billion to 3.5 billion years ago. Those include some heavily mined areas, such as the Appalachians, If a previous civilization had been into serious mining, we'd probably have seen evidence of that by now. There may be nothing left of the mine, but an area without the good stuff and the remains of a big rubble dump would be interesting.

Conversely, a concentration of rusted metal is not likely to occur naturally.

That, and the real smoking gun: landfillite.

Some significant fraction of landfills are going to fossilize into a pretty distinctive sedimentary rock. I don't know what it would look like, but it would have, like, fossil Barbie dolls in it.

I don't think we'd have missed all of them if they existed. We could postulate an industrial civilization which just didn't make landfills? But we've only got ours to go on, and we really like burying trash. If our hypothetical forbearers were anything like us, we'd know about them.

I don't think so. Landfills are a source of many important minerals and energy. I'm convinced that we'll be mining ours in the next couple of centuries.

Maybe, but if so, it will be because we have really substantially depleted primary mines.

A precursor civilization which needed to mine its landfills would therefore undoubtedly have left a visible scar in the fossil record. If they suffered some calamity before getting to that point, then we get landfillite. Either way, I think we'd see evidence of any civilization which sustained the equivalent of a 19th and 20th century.

Not necessarily just due to depletion - could be just better technology (eq. some massive robotics deployment, gassification & atomic sorting, etc.) that makes it a no-brainer to process all regular waste & the old ones when you are at it.

Even modern waste incineration comming quite close with iron & even alluminium collected from the slag & the mostly inert reminder reused in consturction. The local waste incineration plant already covers all district heat requirements of the 400k people city in the summer and is poised to cover 50% of the inter load once their new nr. 3 furnace is installed.

Don't plastics degrade into (effectively) petroleum oil or similar stuff on a geologic time scale?

Wouldn't metal dissolve over thousands of years? I'd be on the lookout for plastics.

> Wouldn't metal dissolve over thousands of years? I'd be on the lookout for plastics.

That's not a bad idea, but finding synthetic isotopes[0] with extremely long half-lifes[1] (e.g., Tellurium-128) would clinch the deal.

[0] https://en.wikipedia.org/wiki/Synthetic_radioisotope

[1] https://en.wikipedia.org/wiki/List_of_radioactive_nuclides_b...

You'll get rust, but huge piles of concentrated iron oxide in a low erosion zone are not found much in nature.

Yes, it will definitely be possible via hundreds of different pathways, some of which they thought of in the paper and others that they didn't.

> The Anthropocene layer in ocean sediment will be abrupt and multi-variate, consisting of seemingly concurrent specific peaks in multiple geochemical proxies, biomarkers, elemental composition, and mineralogy. It will likely demarcate a clear transition of faunal taxa prior to the event compared to afterwards. Most of the individual markers will not be unique in the context of Earth history, but the combination of tracers may be. However, we speculate that some specific tracers that would be unique, specifically persistent synthetic molecules, plastics, and (potentially) very long-lived radioactive fallout in the event of nuclear catastrophe.

One that they didn't mention was our artifacts on the moon which will last 100 million years or so. Geostationary and HEO satellites will stay for a while but I'm not exactly sure how long.

However if you wait 50 million years or so, most of the stuff on earth won't be obvious and you would need to check very carefully.

> One that they didn't mention was our artifacts on the moon which will last 100 million years or so. Geostationary and HEO satellites will stay for a while but I'm not exactly sure how long.

Erosion due to micrometeorites erodes the surface of the moon at 1mm per 1e6 years [1]. I wonder whether erosion of human-made moon artifacts will commence at a comparable rate.

Note that the hull thickness of the apollo lander is just 0.3 mm [2]. Part of the propulsion system, tanks etc. would be the components to last longest, butt 100 million years may be quite a stretch.

[1] https://mauricejscollins.wixsite.com/moonscience

[2] https://space.stackexchange.com/questions/924/what-would-hav...

Well, 100mm is not that much, I suspect there is something in all that stuff that is at least that thick. Maybe the bags of excrement? That would be pretty funny.

Every time this pops up on HN, people post insisting that it won't all go away, that the skyscrapers will, somehow, still be there.

No, they won't. Look at any place in the world where there are mesas. All of the land around the mesa used to be level with the top of the mesa. It has all eroded away, and in only a few million years.

So, the metals will corrode, collapse, and wash away. The stone will erode away. The concrete will erode away. The radioactives will decay. It will all end up as a millimeter-thick layer on the sea bottom, one of thousands of millimeter-thick layers with nothing to call attention to itself. Microplastics will abound, but somebody needs to be looking for them in exactly that layer, the way we found iridium at the K-T boundary layer, after specifically looking. There is a huge overabundance of platinum (parts-per-billion) in layers only 12900 years old, just discovered in the past decade, and only because we are really interested in that layer. (It was the start of the 1300-year Younger Dryas cold spell whose end is the start of the Holocene Epoch.)

Will anything last? Big mining and quarry pits will fill in, but recognizably. Big mine tunnels will fill in or collapse, but recognizably. A rectangular mine shaft dug down through a thousand meters of sedimentary rock will have no other explanation.

Some structures will be buried, instead of eroding away. Those will be deep underground, and then might be exposed again through subsequent erosion or uplift. Again, a brick chimney found buried will have no other explanation, though people will try.

Strictly speaking, one is all you need, but some people ("people"?) need more convincing.

At one level yes, most everything built will disintegrate with time, but we have fossilized footprints from dinosaurs. An industrial society disappearing without a trace seems unlikely. Although the vast majority of the evidence would be lost there will always be traces left if you know what to look for.

The thing is, it’s probably unbelievable when you do find evidence. https://archaeology-world.com/200-million-year-old-shoe-prin...

Interesting article, but unfortunately none of it is verifiable. It cites creationism.org (!!!) as a source and concludes that the fossil shoeprint is regrettably lost.

> It cites creationism.org (!!!)

Ouch... that's an enormous red flag. That irrecoverably tarnishes the entire article.

Yeah, that was part of the point I implied. Much fossils were found before “modern archaeological practices” were invented and used. Now, we only have myths (for lack of a better word) about them. So it only enhances the unbelievability of the item.

Another point that I don’t see made, is that if there was advanced tech, the “artifacts” were likely used until they ceased to exist and/or their purpose was lost.

Just think about our own society. If our entire power grid was lost, we would probably lose the ability to repair/rebuild them within a few generations. There may be pockets where electricity still runs, and some people will remember, but there will be no way to build new computers or phones, so they will invariably be brought to wherever electricity still exists, but even then, the ability to recreate them will cease to exist.

The dinosaurs lived for a couple hundred million years. An industrialized society might last a few thousand.

You'd want to compare the total number of dinosaurs that ever lived against the number of fossil-izable and recognizable artifacts an industrialized society ever created.

True... Assuming that any individual has an equally likely chance of getting fossilized. It also brings up the idea of whether or not we would know if some fossilized specimen or footprint belonged to an animal or a civilized individual.

Those people need to watch a few episodes of the TV series Life After People. Watching it, and realizing that everything around us would literally start to fail in a matter of days without us as its caretakers, really brought home the impermanence of everything. Skyscrapers are certainly not going to outlast ancient cave dwellings. In a matter of a couple hundred years, I would be surprised if a single skyscraper was still standing without us to keep it up. I’ve seen unmaintained buildings falling a part after a mere decade of disuse; a skyscraper lasting for a century or two would be extremely durable on the scale of modern buildings.

Nobody is building for the super long term, we expect on some level that new will replace the old at some point.

This man is trying to build a clock to last 10k years. https://longnow.org/clock/

For what it's worth, the Spivey Building is almost 100 years old and it's been abandoned since the '50s.


St. Louis has a lot of cool abandoned architecture, although you might want to be careful wandering around East of the river.

I wonder how many cities have abandoned towers that became historical places thanks to longstanding traditions of not being able to afford a demolition.

I wonder how long the Egyptian pyramids would last.

As the pyramids are constructed of limestone, they would desolve during the next wet phase of the sahara ( previous wet period ~20kya and 12.5 kya ).


Forget skyscrapers, instead consider this: footprints. You likely made millions of them in your life. How many of them still exist? Approximately zero. It's hard to think of something more ephemeral.

Yet dinosaur footprints have been fossilized. They're found all around the earth.

I'm sure our civilization has already created a gazillion things more permanent than them.

Yeah, but consider the base rate. Even if the things we create are more permanent that footprints, there are just so many footprints that some of them, by unbelievable triple-corner case coincidences, end up here for us. Even if the chance per footprint is really low, there are so many of them made over the course of hundreds of millions of years that it doesn't matter. Our 100 year industrial history is nothing compared to that.

Is total human/intelligent species population not a prerequisite for industrialization. If so, we would expect to see a lot of fossilized remains, which we have not seen.

We have found exactly one (1) skeleton of a Clovis person, the dominant human culture of North America for several centuries, right up until exactly the start of the Younger Dryas cold spell, only 12900 years ago.

Some structures should survive millions of years in dry buried conditions. Like bank vaults made of thick stainless steel buried in Arizona.

I strongly agree with this take.

I've been working on a paper comparing the effects of the Anthropocene to mega catastrophes in the geologically recent past. In addition to the Younger Dryas Impact (12kya), there's the Oruani (26kya) and Mt Toba (77kya) eruptions. From my calculations, it seems the climate change from each of these dwarfs any actions humans are currently capable of, namely petrocarbon burning and also total nuclear war.

I'm also critical of the account given to these events in the IPCC reports.

It seems unbelievable to me that the climate change debate isn't considering these more, so I'm still debugging the numbers and research. But happy to take comments from anyone who's interested!


The earth is warming at a rate of four Hiroshima bombs per second [1] primarily because of human actions. I haven't read your document but it sounds like you're grossly underestimating our energy output.

[1] https://archive.thinkprogress.org/earths-rate-of-global-warm...

Regarding Toba, Le Wik has this to say:

The erupted mass was, at the very least, 12 times greater than that of the largest volcanic eruption in recent history, the 1815 eruption of Mount Tambora in Indonesia, which caused the 1816 "Year Without a Summer" in the Northern Hemisphere.[8] Toba's erupted mass deposited an ash layer of about 15 centimetres (5.9 in) thick over the whole of South Asia. A blanket of volcanic ash was also deposited over the Indian Ocean, the Arabian Sea, and the South China Sea.[9] Deep-sea cores retrieved from the South China Sea have extended the known reach of the eruption, suggesting that the 2,800 km³ calculation of the erupted mass is a minimum value or even an underestimate.[10] Based on new methods (crystal concentration and exponential), the Lake Toba Caldera possibly erupted as much as 3,200 km³ of ignimbrite and co-ignimbrite.

I think its more likely your cursory dismissal which is failing to appreciate the magnitude of this event, than that the person who is actually crunching the numbers is getting it wrong. But what do I know?

I spent some more time on this and now have a comparison table, with citations in my doc. V8 volcanoes still look more energetic and happen once every million years. @ancientworldnow, I'd note that the figure of 4 Hiroshimas/second is the measure of Global Warming, not of human energy production. Hansen acknowledges this in the linked TED talk from your citation, at about 7 minutes in ("it's about 20 times greater than all the energy used by humanity"). To get a sense of comparison, I also found that is the total energy released by a hurricane (note, ~99% hurricane energy is released in evaporation, the kinetic is ~1%):

Mt. Toba 74kya, VEI 8/M8.8 eruption energy: 1e21-1e22 Joules

Global Warming: 7.88e21 Joules/year

A hurricane: 1e21 J

Hiawatha Crater impact energy: 3e21 J

Human energy production 2013: 5.7e20 J/year

Mt. Tambora 1815, VEI 7 eruption energy: 1.3e20 J

Largest earthquakes 2: 1e19 J

Mt. Pinatubo 1991, Krakatoa 1883; VEI 6 eruption energy: 8.3e17 J

Mt. St. Helens 1980, VEI 4 eruption energy: 1e17 J

World nuclear weapon stockpile yield (estimate 2, extrapolated from USA): ~1e16 J

United States nuclear weapon stockpile yield 2020: 1.37e15 J

M8 Volcanoes once every million years, but M7 yield > 10x more energy over time:

“Analysis of this dataset indicates that eruptions of size M8 and larger have occurred with minimum frequency of 1.4 events/Ma… While the effect of any individual M8 or larger eruption is considerable, the time-averaged impact (i.e., erupted mass*frequency) of the very largest eruptions is small, due to their rarity. The long-term, time-averaged erupted mass flux from magnitude 8 and 9 eruptions is ~10–100 times less than for M7 eruptions; the time-averaged mass eruption rate from M7 eruptions is 9,500 kg s1, whereas for M8 and M9 eruptions it is ~70– 1,000 kg s1. Comparison of the energy release by volcanic eruptions with that due to asteroid impacts suggests that on timescales of <100,000 years, explosive volcanic eruptions are considerably more frequent than impacts of similar energy yield. This has important implications for understanding the risk of extreme events.” - Mason et al2

I think you're right, if you take the extreme events that have happened on this planet - and arguably the ice ages themselves also belong there, human activities haven't yet produced anything of that magnitude.

The question is how many more years do you want to give it until we do. These are huge slow systems we are looking at, at the point there is clear evidence around us that disaster is on the horizon, it is already several decades too late to do anything about it.

Previous catastrophes did not vent the millions of tons of hydrofluorocarbons into the atmosphere that we will, that break down into a greenhouse gas thousands of times as potent as CO2. (We thought switching from CFCs to HFCs would save us. Joke's on us!) The total of HFCs currently in circulation, eventually leaked or vented, will produce as much greenhouse effect as all the CO2 currently in the atmosphere. (A sharp minority of the responsible people collect it for disposal.) So, it's not just CO2.

The US is supposed to switch from HFCs to something else around 2024. A lot of companies are switching to propane refrigerant ahead of time because it's cheaper, and worry about it igniting has dissipated, vs. looming ecological catastrophe.

BTW, to my knowledge the Greenland structure has not been reliably dated, nor even confirmed to be a bolide crater (although it seems like one). YD bolide impact seems pretty secure, though.

Temperature change might be a relatively minor effect of the CO2 concentration peak. Ocean acidification causing a collapse at the base of the food web, as marine animals become unable to fix calcium to make shells, might be more important.

It's not clear to me that volcanoes don't release both CFCs and HFCs. Do you have a citation?

I'm looking at the wiki articles, and then at the related chem articles about HFC types and synthesis. I'm not a chemist, but a quick look around makes me think the known CFC, fluorocarbon and halomethanes in volcanic gases would suggest the same or similar compounds as in our engineering uses.

https://en.wikipedia.org/wiki/Volcanic_gas#Composition https://en.wikipedia.org/wiki/Halomethane https://en.wikipedia.org/wiki/Hydrofluorocarbon

On Hiawatha, agreed it's not yet dated, though it is recent: "The age of the crater is presently unknown, but an impact sometime during the Pleistocene is consistent with presently available geological and geophysical data." - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6235527/

They also raise the possibility that some of the radar returns indicate it's still hot in the center of the impact area(!). If so, it's probably one of the YDB impactors.

Btw, there's been another one discovered near it: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL07.... They say they don't think it's related, though it does still have large features that should have been eroded away if it were really old. We'll see!

Has anyone methodically looked for artificial materials like microplastics in the geological strata?

Yes, in that people try and identify what’s there. No, in that it’s not expected to find evidence of a prior advanced civilization. The prior existence of oil as an easily recoverable resource is a strong indicator that nothing like our civilization existed in the last several million years.

Indeed most of our fossil fuels were created during a window in the evolution of life on Earth where plants had developed tough cell membranes that the microbiota could not deal with and transformed the planet into a massive mountain of underbrush in a heavily oxygenated environment. The forest fires must have been spectacular. Trees grew tall and eventually died. Then they fell over, but did not rot. Instead stacking deeper and deeper. This is why we have seams of fossil fuels in the ground to draw from today.

If we wipe ourselves out the following civilization will have a much tougher time getting through their equivalent of the industrial age, especially if they're dealing with the aftereffects of climate change.

But not finding fossil fuels wouldn't tell you anything, because nobody knows how much there ought to be.

If they discovered better sources of energy a little faster, they would stop pumping almost immediately. But for politics, the US might easily have started the switch to wind power forty years ago, and billions of barrels' worth would still be in the ground.

Oil is useful for a lot more than just burning it. Fertilizers, plastics, and asphalt are the most well known but a host of industrial processes use it as a feedstock. It’s only recently that oil has been hard to find, initially it was seeping up from the ground which still occurs on the sea floor in some areas making it hard to miss.

So some other civilization could exist without using it, but they would look nothing like ours.

It is one thing to use it, entirely another to exhaust it. A civilization consuming only 1% as much could look very similar, if it were not dependent on oil for fuel.

We don't need to exhaust it. We only need to exhaust the easy to find sources.

Oil is overwhelmingly used by burning it and its products. Only 4% of it goes to plastic production.

It’s not just plastic but also Asphalt, Lubricants, Fertilizer, etc. However, let’s assume they only used 10% as much oil as us and only used oil for ~100 years before dying off.

They would still have started with easily extracted sources not offshore oil or ultra deep oil. The world had very easily extracted oil when we started. Further, there is no missing oil based on geology.

Oh, you have checked? There have been no dry wells?

I wonder where the term "dry well" came from.

Most dry wells are around oil fields. We have fairly good understanding about the overall geology of oil fields, but you can have a dry well 50m from an active well. What we don’t have is most expected oil fields without oil.

That's true about the oil; coal too. If we're not completely wrong about how those resources are created (there are some alternate theories) then we're the first civilization to use them.

However, most of what I've read about prehistoric advanced civilizations discussed them using crystals (quartz) and deriving energy from the earth. Some form of piezoelectricity. There are theories today connecting earth quakes, quartz deposits, and ball lightning, which could be hinting at an energy source we haven't explored yet.

We sent humans to space and robots to Mars and other planets, we are extracting energy from nuclear fission, we will likely build an artificial star soon enough. It's extremely unlikely that we could have missed some mysterious quartz power source.

That's all nice and dandy until aggressive aliens wielding muskets show up in wood & brass starship: https://en.wikipedia.org/wiki/The_Road_Not_Taken_(short_stor...

The premise of this story is hilarious and wonderful to contemplate as a possible scenario. Food for thought and thanks for the link. I'd never heard of it before.

After a couple thousand years of computational evolution, if you don't think there'd be a possible reason for leaving behind massive silicon crystals... Well, you haven't been reading enough science fiction.

If you could grow pure crystals more easily (thinking Diamon Age), why not have giant plates serving as a piezo generator or ambient electromagnetic waveguide harvesters?

So a civilization thousands years more advanced than us failed to go to space (evidenced by the fact that they did not leave behind any space junk) but somehow produced energy from crystals?

FWIW, space junk wouldn't necessarily survive that long. Things on lower orbits would deorbit themselves quickly without station keeping. Things on higher orbit would get pushed away by solar radiation over long time, and degrade under high-energy radiation (such as UV rays). What remains would be hard to find, because space is big, so it would have to be fairly large and/or fairly reflective for us to notice now.

Wouldn’t any constant force tend to ellipticize the orbit and lead to a return to earth?

Would have to do the math to be sure, but doing some quick simulations in my mind - I believe you're correct, modulo the impact of the orientation of that force changing (Earth goes around the Sun). Let me illustrate with a diagram:

                     (raise apo)
           |                             | 
           |   ->      --->---      ->   |
           +-  ->    -/       \-    ->  -+
               ->   /           \   ->  
             / ->  /    /II\     \  |   -+
       +----+  ->  |   |IIII|    |  |    +- IN SHADOW
       |     \ ->  \    \II/    /   |   -+
       |       ->   \           /   ->
       |   +-  ->    -\       /-    ->  -+
       |   |   ->      ---<---      ->   |
    RADIAL |                             |
     IN    +--------------+--------------+
  (also raise apo)        |
   ((I think...))     RETROGRADE
                     (lower peri)
This shows a body in orbit (the empty sphere) around the body (the filled sphere). The orbit goes clockwise, sun radiation comes from the left, arrows illustrate the acceleration it creates on the body. Simulating it in my head, I believe such setup would lead to the orbit getting elliptical, with the apogee getting larger and the perigee getting smaller, all the way until either the perigee hits the atmosphere or the body reaches escape velocity (thanks to small, but unbalanced contribution labeled RADIAL IN).

I'm not sure how long such a process would take for a satellite not designed to exploit solar radiation for propulsion, nor whether it wouldn't be dwarfed by other orbit-disturbing influences such as the Moon and other planets.

Also: aerobraking a highly elliptical orbit isn't going to leave you much of a satellite to find.

(Note: I studied orbital mechanics in university on Kerbin, under Jebediah Kerman, so I might be wrong here.)

It would only be eclipsed, daily, during a small part of each half-year, no? And, on alternating sides of its orbit.

Usually people blame the moon, and three-body dynamics, for disrupting other Earth orbits.

> evidenced by the fact that they did not leave behind any space junk

Whatever space junk we leave behind will be gone 100 years from now. https://www.nasa.gov/news/debris_faq.html

That’s really not what that means. The 4th satellite Vanguard 1 was put into orbit in 1964 and it’s expected to have a 240-year orbital lifetime despite getting to within 657.3 kilometers of earth. https://en.wikipedia.org/wiki/Vanguard_1

Geosynchronous satellites 35,786 km (22,236 mi) are going to be up there for a very long time.

PS: If you’re interested https://aiaa.kavi.com/apps/group_public/download.php/3172/IS...'

And anything that went to solar orbit will be the more or less for ever, subject only to the slow erosion of thermal cycles over the eons. And all Pioneers, Voyagers and New Horizons will not have to sustain even that, just comic rays.

BTW, it's a bit mind boggling how big and empty even just interplanetary space is - there could be wrecks of an unlucky discovery fleet paying a visit couple milion years ago and we might never find them unless they come really close to Earth or other sensor rich human inhabitted place or possibly still produce some active emissions (outgassing, sporadic radio signals, abnormal heat absorption/radiation, weird albedo variations, etc.).

I think that’s just for lower orbits, I was under the impression our geosynchronous satellites will be up there for millions of years (unless future humanity cleans up the geosynchronous graveyard orbit)

There is the hypthecial concept of a https://en.wikipedia.org/wiki/Nuclear_lightbulb which pending some so far unavailable metamaterial would reach temperatures of up to 20,000°C and generate mostly hard UV-light in a closed cycle.

Which reminds me of some decsriptions of Indian Vimanas, or rather the parts about their engines, which allegedly were made of some crystals.

We know about the KT extinction layer (which contains a lot of iridium, a potentially extremely useful but rare metal) but attribute it to meteorite ejecta. It also coincided with large scale climate and environmental changes. That's the only candidate I know of as a non-geologist.

This argument disproves fossils.

E: To be pedantic, it only disproves most fossils.

And, as predicted by the argument, the fossils don't abound, and to find them you have to start digging.

I wonder if that's always been the case. Maybe humans quickly cleaned up all the easily accessible fossils before realizing what they were. Ancient Greeks thought they'd found a giant's bone and other cultures seem to have used dinosaur fossils as inspiration for myths of dragons. Even western researchers a few hundred years ago thought dinosaur bones were just recent animal bones. Imagine how careless every previous civilization was with them.

Maybe the biggest obstacle to archeology is having people around who are interested in explaining what they're seeing. Science is a very rare thing for human cultures to spontaneously do. Even the 1000s of years old Chinese civilization never invented science and had to wait for it to be imported. I tend to think that human societies naturally actively discourage science because they'd quickly think up and memetically spread myths for any unexplained phenomena then anyone challenging the popular myths would have to be a misfit and that would come with punishment because misfits were generally harmful to society in the short term.

> Even the 1000s of years old Chinese civilization never invented science and had to wait for it to be imported.

This line didn't pass the sniff test for me, so I did a quick Wikipedia check on the history of science in China. [1] Given the fact that Chinese Society has a large population and long written history, it seemed a bit strange to think that science and technology might have been imported from elsewhere 1000 years ago.

It was actually quite cool! Turns out gunpowder and crossbows were invented there for gaining an advantage in war. [3][4] In AD 132, Zhang Heng created the first seismometer to study or detect earthquakes. [2] Looks like China's had science longer than the United Kingdom's been united.

EDIT: added newlines to break up the Wikipedia hyperlinks

[1] https://en.wikipedia.org/wiki/History_of_science_and_technol...

[2] https://en.wikipedia.org/wiki/Seismometer#Ancient_era

[3] https://en.wikipedia.org/wiki/Crossbow#East_Asia

[4] https://en.wikipedia.org/wiki/Gunpowder

Yup. From what I remember my history, it was the other way around: China was ahead to a lot of discoveries, some of which the West has imported only centuries later.

Interesting thought in your second paragraph. Through similar reasoning it would also follow that one of the bigger forces promoting science - or at least applied science - would be war. It's one of those things that keep you grounded in reality - the ship will either sail or it will sink; the shell will either land on target or it will miss. When your invention is going to be put into combat use, you can't get away with nice-sounding stories. You get instant and often visceral feedback.

I'd say so but only once the science is advanced enough to be of more use than technology developed by trail and error and intuition, which is a pretty high bar. Just think that when steam engines were already in use commercially, we didn't even have the law of conservation of energy, and the whole field of thermodynamics was developed afterwards. We made metal and gunpowder without chemistry, electric lights without electromagnetism, etc.

For clarity, I'm not counting engineering and technology as science. You can develop techniques for building ships that float without understanding anything about buoyancy or mechanics of materials but just though gradual evolution of ideas and passing knowledge down through generations of craftsmen.

More broadly: survival. The crop that will grow or wither, the patient who will recover or die. Etc.

That's quite a different concept. Agriculture techniques would have evolved that way but entirely devoid of science or understanding of how they worked, just evolution of ideas ossified into wisdom. Colonists in new countries experienced crop failures because they couldn't predict how things would behave in the different climates/ecosystems and just applied their "dumb" knowledge. I heard about a hunter-gatherer society that used a seemingly pointless ritual to decide where to get food each day. They had only a superstitious explanation of how it worked until we eventually figured out that the ritual was actually a random number generator that helped them to spread their gathering more uniformly or prevent prey from learning their habits or something along those lines. We can do a lot without understanding.

Medicine was a complete shit-show until modern science because people didn't even understand how to test if it caused patients to live or die! Even today in modern China, doctors still prescribe useless herbs based on superstition. They've stripped away the obvious nonsense about stars and planets that it used originally but still explain it using a mythical description of how the body works and how traditional medicines interact with it.

I guess you could say domains involving physical construction that had to be customized to varying circumstances required better understanding of the underlying physical processes at play.

So building war implements, like weapons and armor, and techniques, like how to target a canon, but also non-military disciplines, like the construction of buildings and bridges, the manufacture of commercial goods, etc.

I agree that they'd be underground.

If someone starts looking they will find this layer containing plutonium-244 (which is made by nuclear explosions, 80 million year half life) and microplastics, and yeah that will make it pretty obvious. But I think you're right that if it was even 5 million years in the future you would really have to be looking for it.

I strongly doubt microplastics would survive heat and pressure well enough to not revert back to oil/gas/coal.

What areas on the earth have already endured for 65 million, 100 million,200, 300, 400, 500 million years already without changes? Obviously many areas have been subducted via plate tectonics and after volcanic transformation at depth would leave no artifacts. Would you find gold rings on dinosaur fingers? Gold watches? We know gold can endure, and if these prior saurian techies had adornments, they may end up in sediments that can endure. How to find them? Catscans and MRI imaging could show dense metallic residues in some cases. So far there have been scans done on a few fossils, but if they were not looking for residues of artifacts, such residues may not have attracted attention. Funerary buildings? Pyramids are only a few thousand years old and many millions would turn them to dust on the surface, and subducted ones = melted away. There has been time for a 200 million year old race to be very very hard to find - except on the moon's surface? If there was a moon project 200 million years ago, would gradual meteoric impacts over this time period have buried them beyond finding? Direct impacts would have destroyed them utterly. Indirect impacts gradually bury the surface of the moon with impact scattered rock powder. We know the moon is deeply cratered and has a deep coating of impact dust. Metal landers would endure and gradually get some feet of accumulated dust, but various metal detectors would find them - but a huge area would need to be searched. I assume good dino-engineers would use aluminum and titanium instead of steel/iron, so ferrous metal detectors would not work. Even good detectors of conductors are good for only a few feet. So we may never find evidence of the war between the warlike dinosaurs of earth versus the Insectoids of Ganymede - that was won so decisively by the insectoids 65 million years ago with their impactor...

A highly responsible civilization that achieves space fairing tech could rebuild its environment, leaving a clean planet as a gift for future species to emerge, and move to the stars. Sort of artifical-creationism, but phycally achievable, it's a matter of civilization goals.

Related, I highly recommend the videogame Outer Wilds, which notably includes a 22 min timeloop, and, related to this I'll add a tiny spoiler; an extinct civilization that was responsible enough to not wreck the ecology of a world that could have intelligent life in their future.

Why would they spend resources doing this?

To give the next species a chance to grow?

While a stretch as a motivation, the Uplift saga by David Brin has this as a core point: ecology and biodiversity is important for all the species in these books; planets are leased and used for a while, and then lain fallow to let them regrow and potentially spawn more sentient beings that could then (be helped to) join the galactic community.

Otherwise you get species popping up later to find the device one of your people left that kills you in the plane of existence you transcended to.


Maybe morality, madness, a form of art, investment, or just-because-we-can...

Isn’t a much easier way to look around our planet and search for satellites of past civilizations? Or even on the moon where everything lasts much longer. Long after we and everything of us is gone from this planet moon vehicles and other devices which were left there will likely still be there unless a meteorite hit them.

I don't think satellites stay in orbit for very long - like a few decades at the very most.

Depends on their orbit. LEO will see drag from the atmosphere and will fall from orbit relatively quickly. Geostationary satellites will orbit basically forever.

Won’t solar winds push it out of orbit in a geologically relatively short amount of time?

Some of the Lagrange points allow for more stable orbits so would presumably be better places to look.

Depends on the orbit. Elon's roadster on its heliocentric orbit has a predicted half-life of 15 million years (1)

The moon has been on orbit around the earth for billions of year and will probably remain on orbit forever (whatever "forever" means).

(1) https://www.mdpi.com/2226-4310/5/2/57

I'd say the moon would be an obvious candidate to look at, though no guarantees.

That’s where you hide the first obelisk

Well, according to Mass Effect, we should really be looking at mars

Abstract: "If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event."

I’ve always loved this paper, for its particular combination of heterodoxy and emphasis on testable hypotheses. There are so many things we don’t know about past human civilizations that have left non-geological markers (who were the “Sea People,” the full story of Petra, tons of undeciphered ancient scripts, etc.) that it doesn’t seem terribly strange that an industrial civilization could have bloomed, died, left few traces, and what traces they did leave are the kind only a geochemist or paleoclimatologist might notice.

Sure if they were fond of atmosperic testing of nuclear weapons.

Maybe be the remains of ancient civilizations could be found on orbit? Satellites can stay on geostactacionary orbit for a very long time. Some of them are sent to the "graveyard orbit" the radius of which was the same for Earth even millions years ago. Did anyone actually compared the number of objects there with the number of satellites we made?

Some tongue-in-cheek ideas: Stockpile of synthetic diamonds

A few cemeteries could make for curious fossils

Mines - some caves survived for 200+ million years. Conceivably a part of a mine somewhere could survive, with concrete structural reinforcements and parts of non-corroding tools intact

Impressions of leaves are common in coal. Fossilized remains of industrial society would have been found by now.

If we can detect traces of life (fossils) I am pretty sure we can detect traces of many of the artefacts produced by an industrial civilization.

I don’t know much about detecting traces of ancient civilisations, but I can definitely detect traces of someone who didn’t read the paper in your comment.

There would be a thin layer of highly compressed shoes.

Considering we can measure Roman metal production by the pollution it left in ice deposits in Greenland, I'd have to say "yes".

I admit I did not read the entire publication, but, at least at face value, this seems somewhat absurd to me. Within the past couple hundred years humans have built massive structures in cities that should last for many millions (hundreds of millions?) of years.

I mean, Manhattan may be under water in 100 million years (or, much sooner), but all those gigantic steel, concrete, plastic and glass structures aren't just going to dissolve.

It sounds like “gigantic steel, concrete, plastic and glass structures aren’t just going to dissolve” really depends on timescale, and geologic timescales are far beyond our typical experience.

From the Atlantic article by one of the authors: [1] [2]

When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. Go back much further than the Quaternary, and everything has been turned over and crushed to dust.

[1]: https://www.theatlantic.com/science/archive/2018/04/are-we-e...

[2]: https://news.ycombinator.com/item?id=24601382

There is better argument and it is surface natural resources.

We know, that before industry took off we had huge amount of natural resources almost lying on the ground. Now many of crucial resources have to be dug from huge depths or recovered from dilute sources.

I can't imagine a previous industrial civilization leaving huge amount of resources available on the surface. Almost by definition, industry is about scaling and efficiency and it always look to get to the results as quickly as possible.

Depends on time frame. Plate tectonics will reset things quite a bit over truly vast time scales.

Over shorter time scales this argument mostly holds, though one can imagine an intelligence with technology but with less expansionary drive and conspicuous consumption than humans. This intelligence may use resources more slowly.

There are plenty of places within a two hour drive or train ride from NYC where you can see gigantic steel concrete and brick structures that are less than 150 years old well into the process of dissolving. If you live in prosperous cities and don’t have to maintain property, it’s understandable how you can be unfamiliar with the relentless processes of rust, melt-freeze weathering, erosion, storm damage, how quickly vegetation grows, and so on.

The steel doesn't last too much, this link claims only 1200 years. https://www.quora.com/How-long-can-stainless-steel-last-for#....

I'm not sure about that number, but the ancient the bronze swords are better conserved than the steel ones.

Plastic will get washed away, and glass may get crunched and be difficult to find.

The rest of the concrete has a longer lifetime.

In periods of 100s of millions of years whole continents disappear or move around, new layers of rocks are formed and old layers are buried. The Rocky Mountains formed just 55 - 80 million years ago.

Cities disappear completely. Concrete and glass becomes rock (again), steel is oxidized and is just layer of iron ore. Plastics degradate and breaks into nanoparticles.

As the article speculates, most evidence would be likely something like synthetic biomarkers in deep sea sediments. Traces of industrial chemicals not produced naturally. Wrong chirality in some organic chemicals. Transuranic elements.

Some zircons have been dated back to the hadean era, when the earth was forming. Any information for building something that sticks around long term would be contained in them.

The Authors seem to be saying a visit to a barren planet shouldn't be written off as "no life".

Evidence of civilization could be just below the surface.

To be fair, industrial-level civilization (engines, mass production, etc) doesn't actually require large, reinforced concrete structures[0].

That said, the answer to TFA's question is "almost certainly yes, unless they deliberately tried to conceal geological evidence of their existence, and probably even then".

0: nor vice versa, technically, though the logistics of using pre-industrial steel as building material would be prohibitive. see https://news.ycombinator.com/item?id=24591216

Wouldn’t glaciers grind them to dust?

I would guess that glaciers would encapsulate the skyscrapers and dislodge them from their foundation, and when they receded leaving a huge pile of steel and concrete. Even if that was later encapsulated by magma, future geologists would have to wonder about metal 'veins' that were so structured and why part of the rock was basalt and another part was an exceptionally hard and dense form of limestone.

Note to self. Don't speculate on HN. Got it. :-)

I wonder how it is that the iron in meteorites doesn't just dissolve away. Any thoughts on that?

Those fell in a desert and were then made into jewelry and preserved in some of the best conditions on the planet. And they still look corroded.

At this point I've sort of lost track of the argument. I read articles about how glaciers preserved soft tissue from the ice age (> 22 kiloyears ago)[1], I've got a bit of rock with a perfectly preserved trilobyte from Montana that is over 380 million years old, and yet people reading want to argue in this thread that massive amounts of inorganic structures built by humans to last for centuries will somehow be dissolved/eroded beyond detection in some short period of time.

So it seems unequivocal to me that human impact on the planet will be preserved for millions of years via the same mechanisms that have preserved snapshots of what was going on millions of years ago.

[1] https://www.cnn.com/2020/09/14/europe/preserved-cave-bear-sc...

The meteorites we find fell “recently”? The iron is in a stable oxide?

I don't think so, meteoric iron (according to the wonderful blog series[1]) is early Egyptian.

Iron (and steel) is stable outside the presence of oxygen and water. It doesn't just dissolve. And certainly if it were part of the steel reinforcement inside concrete in a building where special measures had been taken to insure that neither oxygen nor water would come in contact with it (as modern skyscrapers do) would persist for an exceptionally long time.

But I'm just guessing ;-)

[1] https://acoup.blog/2020/09/18/collections-iron-how-did-they-...

If there are two things the glaciers you mentioned a few posts back would accomplish it would be creating cracks that would expose things to water and oxygen, and also expose the resulting heaps to loads and loads of water. This is how stones found in glacial deposits look like: https://sv.wikipedia.org/wiki/Rullstens%C3%A5s#/media/Fil:Ru...

Note how rounded all the stones are. And the stones that are there are generally speaking a LOT more resilient than any variant of limestone will ever be (including concrete).

What about when the skyscraper’s pieces are submerged under saltwater for a million years? Or are covered up by a mile of river sediment and then plunged another 5 miles under the earth for several million years?

Or the concrete develops cracks, allowing water into the steel reinforcement, which expands, further cracking the concrete until it collapses. Like modern bridges.

Excellent yt chan: vlad9vt, just pictures of artifacts and structures set to music https://youtu.be/EHFe10dp0L4

Evidence for ancient machining technology : Saw cuts, tube drill holes etc https://youtu.be/6KUDu40BC5o?t=1197

There are changes in the geological record that are still unexplained, these could be signs of an older civilization.ld

"The Younger Dryas was a period of rapid cooling in the late Pleistocene 12,800 to 11,500 calendar years ago. It followed closely on the heels of a dramatically abrupt warming that brought the last Ice Age to a close (17,500 calendar years ago), lasted for about 1,300 years, then ended as abruptly as it started. The cause of these remarkably sudden climate changes has puzzled geologists and climatologists for decades and despite much effort to find the answer, can still only be considered enigmatic."


You are posting a climate-change denying site as your source for this? Consider me incredulous.

Edit: From my quick perusal, the warming for the Younger Dryas period is not mysterious at all. The main theory is that there was a sudden cooling due to the failure of the Atlantic meridional overturning circulation around 12,900 BC. This cooling was then rapidly reversed back to the median warming trend about 11,700BC.

You have just pushed the mystery back a step. What caused the failure of the Atlantic meridional overturning circulation? What reversed the failure 1200-odd years later?

Evidence for a bolide strike producing a huge meltwater pulse, to start the process, is accumulating, coinciding with extinction of 30+ genera and the sudden end of the Clovis culture. Another strike at the Holocene boundary is less well supported; but we do need a cause.

FTA: "The likelihood of objects surviving and being discovered is similarly unlikely. Zalasiewicz (2009)speculates about preservation of objects or their forms, but the current area of urbanization isless than 1% of the Earth’s surface (Schneider et al., 2009), and exposed sections and drillingsites for pre-Quaternary surfaces are orders of magnitude less as fractions of the original surface.Note that even for early human technology, complex objects are very rarely found. For instance,the Antikythera Mechanism (ca. 205 BCE) is a unique object until the Renaissance. Despiteimpressive recent gains in the ability to detect the wider impacts of civilization on landscapesand ecosystems (Kidwell, 2015), we conclude that for potential civilizations older than about 4Ma, the chances of finding direct evidence of their existence via objects or fossilized examples oftheir population is small. "

These people have clearly never been to the beach--any beach. The oceans are absolutely chock full of our garbage and it is being deposited not only on the ocean floor, but on every shoreline the world over, where much is ground up and still more silted over. Plastic trash wafts the world over. Everything from beer cans to glass bottles to cars to aircraft are strewn through the entire industrialized world, in forests, creeks, and backyards. We have landfills the size of small towns. There are thousands of shipwrecks all over the oceans. Bazillions of items will be fossilized and preserved, and the odds of stumbling over something just digging anywhere will be very high.

This article is completely full of shit. Humans have left their mark and our junk is going to be here, fossilized, for eternity. If we've discovered hundreds or thousands of fossilized dinosaurs from over 100 million years ago, when there might be only a few thousand such skeletons even to be found, there's a damn good bet that someone is going to find one of the tens of billions of beer cans or beer bottles that are lying around, even if only a tiny fraction survive the aeons.

You've provided a good argument that it's obvious _right now_ from our junk that we live here, but what of that do you expect to last, and how long? Pick a type of object or two and let's look into how they are expected to last and what they'll look like.

Fossilization isn't a universal process, there's no such thing as a fossilized beer can.

Anything corrosion resistant that ends up entombed in geologically stable strata will stick around. There will be lots of anamolous ceramic and glass mixed in with the fossilized human bones strewn about.

Or even just leaves an imprint in the surrounding strata, but it itself does not survive.

Thing is, unlike dinosaur bones, beer can or bottle can't survive for aeons.

Sure they can, if surrounded by stable strata in the same way that dinosaur bones were. In fact, beer cans can bottles won't be broken down by natural biotic processes; they just need to be protected from erosive forces.

but styrofoam lasts forever /s

For sufficiently short values of forever.

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact