The History Channel had a 20 episode series called Life After People that looked at what would happen if every human suddenly disappeared.
The National Geographic had a similar, but only one episode program looking at that questions, called Aftermath: Population Zero.
I have a vague recollection of seeing something like this on one of Discovery's channels, too, but I may be mixing that up with an article in their magazine.
My recollection is that they all concluded that in the very long term (tens of millions of years), if some other species evolved intelligence it would probably not be able to tell we were here.
Some of the materials we used might survive, but things like glaciers in ice ages would grind them to a powder. The next intelligent species might notice these odd concentrations of unusual combinations of metal particles and powdered long chain carbon compounds, but there would be nothing to tell them it wasn't made by some unknown natural process.
I've always wondered if future people will believe that we put up the all our artificial satellites, without help from aliens. If we can't even imagine egyptians being able to stack rocks, who's gonna believe that we forged metal ships and launched them into orbit?
I would expect geostationary satellites to last pretty long, after all their orbit should have close to zero atmospheric drag and barely any tidal forces.
ice ages are a cycle and happen about every 100,000 years. although we are likely triggering the next ice age a little early with our environmental impact.
PFAS sediments in ice and ground layers, coupled with the insight into how PFAS-materials are made via non-natural processes should do the trick for many million years to come.
> The next intelligent species might notice these odd concentrations of unusual combinations of metal particles and powdered long chain carbon compounds, but there would be nothing to tell them it wasn't made by some unknown natural process.
So our fossil fuels could be the remnants of some long gone civilization?
There are many fossils we have of life from tens of millions, and hundreds of millions of years ago.
Humanity has covered effectively the entire planet with items, human bones, and structures that will fossilize and make it pretty clear that an intelligent species was present.
The SURFACE of the Earth might not show it, but the fossil of the human femur with a knee replacement, or the plastic GI JOE that fossilized in mud, or the fossilized remains of any number of concrete structures around the world would clearly be visible with a little digging.
Many continents will undergo subduction, others will be flooded, or covered in glaciers, but there will be some areas that endure without much disruption.
Ceramics should last a very long time if they are buried. Ceramic toilets and stoneware dishes are like stone. If buried in sand or silt that collected over time they would be like other fossils. They might get crushed or broken, but I don't think they'd dissolve or corrode.
Yes we have fossils of many of the most delicate creatures that have ever lived, it seems impossible to believe that nothing of all the durable items we have created would remain or be fossilized. It’s a cool thought experiment wondering if we aren’t the first but it seems completely impossible. I’m afraid our generation will be known as “The Plastic Generation” from our layer in the sediment.
"I'm afraid we'll be called the plastic generation", why are you afraid?
Plastics are a hallmark of an era, like clay, bronze, bones, etc... .
Social and regular media is currently making plastic out to be this big boogie man, intentionally ignoring the good sides of plastic, to sell you tweets/articles about the benefits of plastics (and will point out how you should suddenly feel bad for not using them already) in a few years anyway. They're not about a balanced discussion anymore.
How would plastic kill us? The only issues I'm aware of are
1) the pollution of oceans, which seems very fixable with much less effort than replacing plastic (filtering water at river outlets and in coastal waters, preventing ships from just dumping their stuff everywhere).
2) microplastics. In marine environments that seems solvable by solving point 1, and while a cause for concern I don't think any negative effects outside marine environments or food chains containing marine animals have been shown?
Of course particulate matter is somewhat related, but wheels on asphalt will cause tiny airborne particulates no matter what material we use to make tires, so we might be better off just filtering our air in any case.
Yes, we need to stop using so many harmful things. It is becoming clearer by the day that the trade-offs are untenable.
It is true, it will require a significant recalibration of our current methods. But engineering challenges are fun, interesting, and beneficial. The chance to improve our survival and give ourselves the chance to thrive.
Why turn down this opportunity for the sake of empty pedantry?
Mainly because plastic is not nearly as cool as stone or bronze. Plastic also has connotations of disposability and superficial qualities that unfortunately seem to describe the worst of this era also.
Nah, molds are already evolving to eat plastic in landfills. The fact that until now life hasn’t adapted to plastic as a good source indicates that no prior civilization had developed plastics before, or else it’d already be biodegradable.
But plastics don't occur spontaneously in nature, do they? So why would any species of plastic eating life form survive until our days after running out of all the available early plastic?
Generally speaking organisms of today retain the adaptations of their ancestors, at least to a measurable degree. Whatever organism that ate plastics back then is unlikely to have gone extinct but rather gone back to whatever it was eating before, while retaining the plastic metabolism. Within the span of hundreds of thousands or millions of years (e.g. when a prior evolved primate would have had their technological period) those adaptations would probably remain intact and their descendants would be munching away on plastic today. If we suppose that the plastic culture existed further back than that, then there might not be organisms with intact metabolisms, but nevertheless there'd be some residual proteins that had an enzymatic decaying effect even if the organism didn't make good use of it. The fact that plastics have shown no deterioration at all for extended periods of time seems to indicate that nothing which survives today in contact with plastic has any lineage back to organisms which once consumed plastic in the past.
Now that's an interesting thought - look at biological adaptations in the ancient ancestors of existing animals. If a 40 million year old extinct insect appears to be able to process plastics, that's a pretty good indication that _its_ ancient ancestors had a diet of plastics. Biology might just be the "last artifact".
I suppose that's not terribly useful when looking at mars though :P
I like the idea that we are the biologic boot loader for AI, as Musk put it.
Imagine that biologic creatures evolve over time long enough to develop, birth, and disperse AI out into the greater universe - and collapses after doing so. it takes a very long time for another civilization to evolve to the point that it spawns another AI form into the universe, and all remnants of the prior are gone.
Gah - I just mean I enjoyed the thought experiment of his statement.
If you are not aware, Elon said this on his appearance on Joe Rogan.
Over timescales of hundreds of millions / billions of years, preservation of an object outdoors in the elements is vanishingly-likely because mechanical erosion and chemical corrosion will attack every substance. In a cave or somewhere else protected, preservation over longer timescales is much more likely.
It's also worth nothing that several billion years from now, the Sun will turn into red giant and the Earth's atmosphere and surface will be vaporized and left as a sterile rock over tens of billions of years. That is, unless we manage its supply of H/He by managing its fuel from burning up too quickly, which could extend the life of the Sun by several to ten billion years. Star fuel management is a difficult but necessary problem for advanced species to solve.
Well for one thing, any ceramic or other durable remnants of a civilization prior to ours would only have had to have lasted for several hundred million years at most, not billions, since before several hundred million years ago life of such complexity would have been vanishingly unlikely or impossible. Secondly, for any prior civilization, the whole sun and cinder thing doesn't apply anyhow and finally, if we or some civilization before ours had vanished, at least some of our durable goods would be conserved in some sort of preserving environment. As another reply here mentions, we have wonderful fossils of some extremely delicate creatures from deep history, a toilet or two would hardly need much to pull off the same degree of conservation and later be discovered. Your notion of it being extraordinarily unlikely doesn't really fit existing circumstances.
> Star fuel management is a difficult but necessary problem for advanced species to solve.
I imagine that's not necessarily true. It may be that advanced civilizations harvest energy from stars, but live in interstellar space ships (which would also explain why we can't spot evidence of them).
That's assuming it would be worth the investment (because systems in most areas of the observable universe can be few and far between) to go to other systems, when you could invest in preserving your own home system by exploring and colonizing planets, planetoids and such around the home-world. When you commit to interstellar travel, you basically need an entire planet's-worth of supplies, energy and biosphere or you send self-replicating robots.
It's not like we can miracle up another Earth or go to another solar system anytime soon. Our best bets are to preserve what we have and have a look at the moon, Mars, etc.
If we had any reason to go there we could build a starship that can reach Alpha Centauri in 100 years or so travel time [1]. Building a ship of a few hundred meters diameter and stocking it with a supplies for 100 years and a few thousand thermonuclear bombs as fuel would be a giant effort, but very doable. Once you have civilization on both ends of the journey you can probably set up a less energy intensive travel method (maybe a scaled up skyhook [2])
Actually, it might be. One solution to Fermi's Paradox is the idea that we can't see other alien species because they're hiding from potential predatory alien species. Hiding in the vastness of interstellar space would in that scenario be a very good move.
Sure, but stars have the majority of mass in a solar system, so you might want to basically deconstruct them to make more ships/habitats. See Orions Arm/deep well industrial zone as an example. :)
We know the expected isotope ratios too well and test them too often. This is how we discovered evidence of a natural nuclear reactor from 1.7 Gya. Any other nuclear civilization would have changed the isotope ratios in detectable ways in some part of the world.
Out of interest what was this natural nuclear reactor? And also how do we know it was definitely natural? I don’t believe it wasn’t natural, but I wonder how one would prove that.
>Or someone later wouldn't know about us.... outside say an abandoned car floating through space...
The cars we left on the moon will still be there. The satellites and trash in orbit would still be there. The satellites orbiting Mars would still be there.
We can see clear evidence that life has altered the climate in the past [1]. Anyone looking like we are would notice our mark on the environment.
Low-Earth orbits will decay over periods ranging from years to millennia, based on residual air resistance.
Those effects are minimal in geosynchronous orbit, though there's still some residual atmospheric drag which might be significant over millions to billions of years. The period under concern is roughly 5 billion years, at which point the Sun will have ballooned to a red giant, enveloping the Earth. (Increased solar radiance, as well as various cycles and changes on Earth will likely have long made it uninhabitable by life within the next 800 million years or so.)
Other effects include solar wind, possible interactions with the Earth's magnetic field, precessional effects caused by the Earth's axial tilt and irregular geometry (to use that word in its literal sense), as well as gravitational perturbation from the Moon and possibly other bodies within the solar system.
There's a slight possibility of impacts, though those would be highly unlikely -- space is big, as Doug said, and satellites tiny. Even the Earth only gets wallopped every few tens of millions of years. Though any such impacts might create a sufficient debries field within the orbital zone to affect other satellites. The Geostationary band itself is quite narrow, and preferential placement is above the equator, which would focus placement for potential interaction.
Depends what you consider "closer". Geosynchronous orbit is 35,786 km above the surface and while at 500 km you get significant decay (order of years to re-entry) while satellites at 1,000 km are estimated to take centuries to re-enter. Extrapolating that anything above the start of medium earth orbit (2,000 km) and out should last a hell of a long time.
Will our geostationary satellites still be there, say, 50 million years from now? The lunar landers probably will be, unless meteorites take out all the landing sites.
They will be somewhere around Earth. But not on the orbits they are now. They won't be hard to spot.
I guess the most pressing evidence is that nobody used the fossil fuels before us (at least in large quantities), and a lot of it is from the time that plants first colonized the dry soil.
We have some very good explanations for the distribution of fossil fuels, with a lot of predictive power. They would all be trash of some thinking being decided to take some of it our.
But if some being had decided to take some of it, we could still have explanations that seemed good to us and that fit the distribution of what we found. And we would use the match between the theory and the actual distribution to confirm that the explanations were correct.
My understanding is that I would expect there would be some left, albeit maybe more debris after their orbits slowly become more erratic (not as coordinated regarding other satellites) and collisions and failures occur.
If another civilization had reached space-faring technology then one day they might come back and discover that the (perhaps inhospitable) home planet...harbors again life. Probably too far-fetched and better suited as material for a scifi story, but the idea is interesting.
> Probably too far-fetched and better suited as material for a scifi story, but the idea is interesting
M. Night Shyamalan directed a terrible movie from 2013 that is a version of that premise. After Earth, starring Will and Jaden Smith. Solid idea for a sci-fi movie, they botched it unfortunately.
"In the future, an environmental cataclysm forces the human race to abandon Earth in search of a new habitable planet, eventually settling on the planet Nova Prime" ... "A crash landing leaves Kitai Raige and his father Cypher stranded on Earth, a millennium after events forced humanity's escape. With Cypher injured, Kitai must embark on a perilous journey to signal for help."
How long does it take for tectonic action to "recycle" the plates? Could a civilization have existed as extensive as our own in the extreme past, but we can't see any evidence because it is all hundreds of miles under the surface of the earth being melted down slowly?
Oil was a good push for the development of our civilization, and should have been for any past technological civilization too. If we have oil today (in the amount we are getting it, at least) then the previous civilizations didn't reached our oil dependent civilization stage, or existed before the actual oil reserves formed.
It doesn't imply that there wasn't any civilization before, but or it happened hundreds of millions of years ago, or never became as advanced or global as our actual one. Unless there could had been back then an abundant energy source different from oil but with similar efficiency, and it got globally depleted by that previous civilization.
The same argument can be made for rich surface deposits of Iron, Aluminum, Tin, etc... If there were civilizations in the past - even a hundred million years ago - they likely would have mined those.
If a previous industrial civilization put satellites into geo-stationary orbit, they'd still be up there. If there are unknown objects in geo-stationary orbit, would be be able to find them? If we could find them, and we haven't, doesn't that put an upper limit to the technological sophistication of possible previous industrial civilizations?
"Geostationary" might have been rather lower in elevation than today, depending on when in time that civilisation might have occurred. The rate of decrease has not been constant with time, and may have been roughly constant from ~2.5 gya to 600 mya.
During the Precambrian era, the Earth's day was ~21 hours long, and a geostationary orbit would have been about 32,265 km rather than 35,787 km today.
So the satellites might not be precisely where we're putting them, but:
1. We'd all but certainly spot them.
2. The elevation / orbital period itself would give a very strong indication as to when the civilisation had existed.
Not necessarily. It is true that the industrial civilizations we know of, considered on a consolidated planetary short-recent-history level, have launched satellites in geostationary orbits. But we can not logically infer from this that only the ones we know of have launched satellites in geostationary orbits. There may be ones that have launched geostationary satellites which we do not know of.
Isn't there some level of radiation that is ubiquitously present ever since we started nuclear testing? Seems like we could figure out if there ever was a nuclear-capable society in the past just by looking at radiation decay.
I remember reading about that on wikipedia years ago. Don't remember the name, but it's the site of a large crater, and I think there was also glass in the area similar to what's created by modern nuclear explosions.
>The current area of urbanization is less than 1% of the Earth’s surface
But doesn't this assume cities are distributed uniformly and randomly? Cities seem to be build at ports (ex: Port of NY, Oakland) and waypoints with natural resources or barriers (Salt Lake City, Denver on either side of the mountains for example)
We know the general distribution of continents dating to 550 million years ago (Gondwanaland), and to some extent prior, though that largely predates the Cambrian explosion of complex life on Earth.
Ancient coastlines, estuaries, and riverbeds leave quite distinctive geological traces and would be detectable. We'd be looking for ancient civilisations on or near such features.
That's a good point, I just meant that it seems odd to focus on cities. (Especially since while the cities themselves are small, the swathes of land to supply them aren't. Also I think someone else commented evidence of atomic tests would persist a very long time, for example?)
It also assumes industrialization similar to our own. A past civilization would most likely have developed entirely different technologies that we may not know what to look for.
This reminds me of https://www.brainyquote.com/quotes/daniel_patrick_moynihan_1... “Everyone is entitled to his own opinion, but not his own facts.” they wouldn’t have developed their own physics and universal constants. Of course if they were tens of 1000s of years ahead of us and deliberately cleaned up who knows what’s possible. We could be the evolved pet like in red dwarf
Some technologies seem too universal to assume an industrial civilization would miss them. Things like ceramics for example are easy to make, very useful and would likely survive in the geological record.
sorry for the total aside, but this article reminded me of one of my deepest typo curiosities: why is the misspelling ratio -> ration so common? there are lots of words that can have a character erroneously appended and still be a correctly spelled (different) word. for example: most verbs in english (ride -> rides, bake -> baked, etc.). but for some reason, I see ratio -> ration all the time. 'n' isn't even that close to 'o' on the keyboard! it really jumps out when you subvocalize; the 'n' changes the pronunciation a lot.
Not sure if it would be this, but autocomplete on some platforms sometimes happily replaces a correctly spelled word with a different word it incorrectly assumes makes more sense contextually, and you won’t notice it happened unless you’re paying close attention as you type.
You can sometimes make it less aggressive. I turn off autocomplete completely because my phone has a hardware keyboard, but I set it to medium for the software keyboard (in landscape mode or if I bring it up manually).
I wonder if it has to do with the suffix -tion. Maybe muscle memory is triggered when the letters “tio” are typed at the end of the word and “n” is automatically added to the end of the word.
I'm fairly sure this is why I do it. I'm an average typist and above-average speller, but -ion spills out whenever I type it. There are almost no words ending in -io, and there are a lot ending in -ion. For some quick numbers, the OSPD database I have here has 1432 -ion words and only 47 -io words.
I do this all the time. When I was young I believe a saw a ratio-n typo in a math textbook, and for many years I believed that it was a synonym. Like a fraction, but a ration. Combine this with the -tion problem that others have mentioned and it definitely rolls off the fingers quite easily.
We would know it. We probably wouldn't know much about that civilization; almost all of their culture or art would not survive. But we would find bits of glass or pottery fossilized in rocks at the very least. We haven't found anything like that so it seems extremely unlikely.
What Fossils Will We Leave Behind in 65 Million Years?
65 million years ago the dinosaurs died out, we only know of their existence because of the few fossil remains found. So what if a similar fate were to happen to us humans tomorrow, in 65 million years time what would remain of everything we had created and would there be anything be left for any future intelligent species to find.
They glaced over nuclear war a little too quickly. While I'm not an expert, I've heard many times that a significant nuclear exchange between countries would likely result in so much debris being thrown into the atmosphere it would cause a nuclear winter. This could lead to a full blown ice age, mass extinctions, etc...
Surely those "side effects" of the bombs would be measurable far longer than the radiation. We know of past super volcanic eruptions and the dinosaurs' extinction because of similar circumstances.
It’s not just radioactive material that would betray a past nuclear war. Some of the stable decay products are extremely rare in nature, and their presence in the ratios we know atomic weapons produce would be a dead giveaway.
Just thinking off the cuff and channeling a bit of Isaac Arthur here.
Coming from the angle of a non-native intelligence colonizing Earth in the super distant past, there may not be many or any terrestrial remains over such a long span of time.
It’s reasonable to think “aliens” would not burn coal and oil for energy. If they crossed the gulf of space, they likely used fusion or some other power source. A ground side civilization could sift helium3 from the oceans for thousands of years without a noticeable depreciation. If they used power satellites, those would likely have fallen from orbit or been knocked out of the Earth-Moon system within hundreds to thousands of years.
Within human history, many of the same geographical areas of the world have been good places to live for thousands of years. But when you extend that to hundreds of thousands to millions of years, those places generally change drastically and disappear. One could assume, for the sake of argument, that aliens colonizing Earth might have similar biological needs as we do and would live in similar areas of the distant past. We might not easily find those places now given environmental changes over geological ages.
We also are still very early in exploring the solar system. It’s plausible there could be remnants of mining and manufacturing in places we haven’t looked. It’s important to remember that if your civilization is colonizing a new system, you’re already a space based society. It’s then reasonable to expect little on the ground industrialization since most of your infrastructure will be in space.
There’s a new study talking about solar electrostatic effects on the Moon and how it causes lunar dust to rise and drift around despite no atmosphere. Given long enough spans of time this might even conceal evidence of prior space-based industrialization.
One big red flag to me that this hasn’t happened in Earth’s history is the biological record. We have a fairly good overall map of biology over large areas of the world. Everything alive here seems to come from here. There’s nothing alive that doesn’t appear to use the same general base chemistry and biology as everything else.
If some aliens showed up a hundred million years ago, we might expect to see some distantly evolved branches of life that are somewhat different in at least DNA or other chemistry. We might find something like this but it’s unlikely.
The follow-on to that might be an argument that all current life is descended from some ancient aliens. That could be true but it would be nearly impossible to tell at this point. All life seems to have a common descent with no aberration, so following up on this line of thought is extremely difficult to test for. We would need to find examples of life outside of Earth before we could make comparisons to investigate that hypothesis.
I suppose it’s possible an ET civilization had an outpost on earth and that outpost is now in the middle of the ocean. I think the discussion is an earth based civilization, then the chances of all their cities, discarded equipment, lost items haven’t left a single mark is very unlikely.
Right but I think in terms of interstellar colonization there can’t really be a concept of an outpost how we think of say bases in Antarctica or the ISS. If you’re sending people to another star system, it has to be a minimum viable colony or nothing.
In regards to fossils, excellent point. The problem is that despite all of the fossils we’ve found, overall it accounts for less than 1% of all species that have ever existed on Earth. The odds of finding even a single fossil from an animal from a non-terrestrial colony are exceptionally low. Not zero, but so low as to be extremely unlikely.
In some ways, Howard's Hyborian Age stories featuring Conan were a response to scientific revelations of his day indicating the plausibility of a vanished age prior to recorded history.
Aschulean hand axes have been dated to 1.76 million years ago, Oldowan tools were made up to 2.6 Mya. Just really smart apes, sure, but who would know if they had a breakaway 5,000 years of brilliance reflected mainly through an extensive oral tradition and crafts with exceptionally disposable materials.
Not known in Howard's day, but Göbekli Tepe is an extensive temple complex in Turkey that predates when we thought sophisticated organized societies emerged, and seems like something his Hyboreans might have built.
If you want to get way out on a limb, our theory about how monkeys got to the new world is pretty suspicious. Currently, we theorize that a breeding population managed to accidentally raft across the Atlantic exactly one time in all of history, but this is so rare it didn't happen for other animals, and never took them to the much closer North America from there.
Might as well guess some ancient extinct navigators brought some monkeys along as pets, then died out and left the monkeys as the only evidence. Crazy and unsupported conjecture, but why not, par for current theories.
I’m also reminded how in the past 15 years or so, using LIDAR, we are learning that there are way more Mayan or Aztec ruins than previously thought; they were just covered up by the jungle.
There’s a lot of mystery still buried in the earth.
A minior plot point of "The Light of other days" by Baxter and Clarke was an earth civilization 3 billion years ago which was destroyed by an asteroid hitting earth that wiped the surface clean.
That reminds me of the Troodon dinosaur. It had a large brain size compared to its body. I think I recall reading Troodon's brain left marks on its inner skull. It was supposedly very intelligent due to its brain size.
This idea has come up a few times on conspiracy subreddits, but it seems like a pretty big stretch. Look at all our landfills full of old obsolete electronics. The fact that we don't find similar things make these "hidden civilization" theories pretty unlikely in my opinion.
The National Geographic had a similar, but only one episode program looking at that questions, called Aftermath: Population Zero.
I have a vague recollection of seeing something like this on one of Discovery's channels, too, but I may be mixing that up with an article in their magazine.
My recollection is that they all concluded that in the very long term (tens of millions of years), if some other species evolved intelligence it would probably not be able to tell we were here.
Some of the materials we used might survive, but things like glaciers in ice ages would grind them to a powder. The next intelligent species might notice these odd concentrations of unusual combinations of metal particles and powdered long chain carbon compounds, but there would be nothing to tell them it wasn't made by some unknown natural process.