This episode is sponsored by Audible. Our civilization is ancient, with ruins of
its early incarnations going back many thousands of years, but thatâs just an eyeblink against
the age of our world. If we disappeared tomorrow, would the scientists
of some successor race, millions of years from now, even know we existed, and if not,
can we be sure we truly are the first civilization to arise on Earth? So today we will be looking at the Silurian
Hypothesis and the general surrounding topics of if our civilization would leave any long-lasting
evidence if we somehow disappeared tomorrow or if we would even know if some other civilization
had existed here on Earth. That last one is a bit complicated by potentially
coming in two forms, life that previously arose here â like if the dinosaurs had gotten
high tech and then blown themselves up â or alien life that had colonized Earth at some
point and that colony had failed. Now today is another Sci-fi Sunday episode
here on SFIA, where we try to look at concepts from science fiction and ask how scientifically
plausible they are, and since this has been a popular topic in sci-fi for over a century
now, unsurprisingly, weâre not the first to look at this from a realism perspective. Indeed the name Silurian Hypothesis was coined
by Astrophysicist Adam Frank, and Gavin Schmidt, Director of the Goddard Institute for Space
Studies, back in 2019 when they wrote a paper up, trying to analyze how long we could expect
to see ruins of civilizations for. Silurian is a reference to Doctor Whoâs
race of lizardmen, who arose on Earth long before humanity did, not to be confused with
the Silurian Period of Earth, a roughly 25 million year long period 419 to 444 Million
years ago. That draws its name from a Celtic tribe in
Wales, where the first rock strata of the period was identified by Roderick Murchison,
and was inspired by his friend Adam Sedgwick who had named the Cambrian Period, 485 to
541 Million Years ago, after Cambria, the old Latinized name for Wales. The period between the Cambrian and Silurian,
the Ordovician, is named after a Welsh tribe. Iâm probably botching some of these pronunciations
incidentally, so donât use me as your reference, though Iâm never a good pronunciation reference
for anything with the letters R or L in them anyway. The Silurians from Doctor Who are named-after
the Silurian Period â making their first appearance way back in 1970 when we were just
getting introduced to the Third Doctor. In that, he notes that they should really
be called after the Eocene, the period 34 to 56 million years ago, post-dinos. And again, this isnât a super-new idea. Almost as soon as we started getting strong
evidence that our planet had been around a million times longer than humanityâs recorded
history and that the Universe was huge and full of stars like our own Sun, folks began
contemplating if civilization might predate humanity. All at the same time, we were finding ever
older ruins of human civilization that made the âAncientâ era of around 1000 BC, prior
to the rise of Classic Greece, seem downright recent. So sci-fi from the early 20th century had
ruined human and alien civilizations that were older than the dirt in more books than
I can count. The entire Cosmic Horror subgenre of authors
like H.P. Lovecraft is built around it and so are a
lot of the Sword & Sorcery genre of folks, like Conan the Barbarian and Elric of Melnibone. It definitely saw a resurgence in the 1970s
though, between the Space Race and books like Chariot of the Gods, that focused on the notion
that our own ancient civilizations may have met advanced aliens and viewed them as deities. Now there are a lot of reasons that this is
contraindicated, see our episode: Ancient Aliens, for more of those, but the one that
always bugs me most is the implication that some of the great works of these ruined empires
we dig up, canât actually have been their own designs, and that they had to have borrowed
or stolen them from aliens. Now to be fair, thatâs not really an argument
based on evidence, and indeed they probably did borrow or steal a lot from other civilizations. It just would have been their neighbors or
predecessors, not advanced aliens. And thatâs kind of a critical point, folks
often note parallels in ruined bits we recover, be it pyramids in Egypt and Mesoamerica, or
a specific style of art or type of technology. And that has to contend with remembering our
ancestors were quite mobile. They only had feet, theirs or maybe some animalâs,
but they were pretty enthusiastic in using them. They were also more or less just as smart
and curious as we are nowadays, so someone bringing a sketch of some sight they saw across
half a continent of some cool building to show their king is not even vaguely unrealistic. What is a bit of a problem though, is that
unlike our fossil record, which honestly is pretty scant itself, thereâs not a million
year chapter containing a trillion organisms that were on a step from the original critter
to its new mutated form of which a few hundred fossils might realistical have been made and
a few discovered. Art and Architecture certainly could be viewed
as evolving with lots of early examples, but at the same time it is a much smaller sample. Someoneâs artistic style evolving from one
period to another might only have included a couple dozen finished products showing their
trajectory. And you probably donât really get a lot
of transition pieces showing the migration or evolution of many technologies or art styles
even just a few millennia old. So we can have a bit of a problem trying to
show the evolution of some building style or pottery style and how it migrated across
Eurasia or down the Nile, which has a lot of history buried in its floodplain and delta. This would be even harder if it were millions
of years, not thousands, and if entire continents were moving around and dipping under the sea,
which is exactly what we think they were doing on those timelines. So how long does stuff last? Not long, but also a long time, and I should
start from the outset by saying this one is a lot like how far you can see a radio signal. Thereâs no limit to how far radio signals
can travel, excluding hubble shift, but youâll hear people say we couldnât hear one beyond
a handful of light years, which kinda ignores all that radio astronomy we do even millions
of light years away. Thereâs no limit to how far those photons
can travel, it is a question of how big the signal is, so to speak. A very high power signal thatâs just pulsing
at a low frequency just doesnât blur much over distance, even over galaxies. Of course, nobody really would bother using
that sort of signal for in-system communication because you could be cramming far more conversations
in, like we do. And those are the sorts of signals we expect
to be mostly overhead signals, whereas the type I described is what you use when you
want to be heard over long distances by people who donât necessarily have mega-receivers
or even know youâre talking, what weâd call a beacon. In that context we need to keep in mind that
civilizations might be leaving time capsules behind that are built with the specific intent
of being findable and still sturdy, millions or even billions of years later. In neither case, distant alien radio or ancient
time capsules, are we assuming that this is anything like their day-to-day operations,
but we have an entire niche industry for manufacturing time capsules which Iâm assuming means we
sell thousands of them a year. Now they wouldnât last millions of years
but thatâs a limit on our current technology, not intent. We have materials that would do the job incidentally,
itâs just they tend to be way more expensive than a personal time capsule that someone
is looking to buy on Amazon, for maybe a hundred bucks. We should assume that will change the longer
weâre around, and we also need to acknowledge that we, thus far, do not have the technology
to kill off all of humanity or even really set us back more than maybe a few centuries. Even at the height of the cold war we lacked
enough ordinance for that, commentary about us having enough bombs to kill everybody ten
times over again were utter hyperbole. We could build enough big bombs for that,
but theyâd get pricy to maintain and more importantly, they need expensive rockets to
get where you want them to and bigger payloads equals more spending and the nuclear arsenals
maintained by both sides were already painfully expensive on the national economies of those
involved, boosting your arsenal up tenfold more wouldnât have achieved much of strategic
value and would have crippled their economies. Or basically, we can say with a decent deal
of certainty that civilizations canât wipe themselves out till they exceed our current
technology level, and thus would have time capsule tech at least as good as ours. Though of course technology need not proceed
in unrelated fields at the same rate it did for us. Now we discussed the difficulty of keeping
any sort of machine functioning for long times in our recent episode the Million Year Machine
but proof of existence is a bit different. As an example, we have lots of things left
over from the distant past in fossil format and if a tree can survive as a fossil for
386 Million Years â the current oldest tree fossil from a quarry in New York â then
so can a lot of dimensional lumber and the big giveaway that youâre looking at the
remnant of a technological civilization is all the weird right angles you would find
in the geological record. Geometric shapes can occur naturally but mostly
wonât. All those basements and foundations that would
get flooded and eventually filled with sediment, some are going to end up getting dug up millions
of years later. We get banded deposits of iron leftover from
the ancient pre-oxygen period of Earthâs atmosphere, those are intact bits of iron
over a billion years old, because of course stable elements donât decay with time. Theyâre still iron and theyâre still titanium
or aluminum, which doesnât corrode, or gold, silver or many other metals that we have shaped
into suspiciously unnatural forms. It's a bit of an unknown how long plastics
would persist or how theyâd fossilize and we really canât say how easy it would be
to figure out you were looking at a freeway someone built a billion years ago. For my part, I just really donât see a scenario
where all those right angled foundations in all those houses and skyscrapers, and all
those wheel-shaped hubcaps and all those roads with driveways running perpendicular off them
are going to somehow vanish universally and not seem really obvious later. Now critically, it is a bit of an academic
issue anyway because we can pretty conclusively rule out historic high-tech civilizations
on Earth, and as weâll show in a moment, we can also flip it around and show why a
post-human civilization wouldnât have any problem seeing us, because it wouldnât be
long before they arose. Now we cannot conclusively rule out aliens
starting life here on Earth, but we can say they pretty much needed to have done it on
Day 1. We do not have the DNA of anything fossilized,
and weâre not optimistic about finding viable DNA in any ancient fossils, even using some
of the techniques we contemplated in our De-extinction episode for recreating DNA from decayed or
damaged DNA. Nonetheless, while our fossil record is scanty,
it shows a pretty clear path of evolution and divergence. I mean we could be tricking ourselves into
seeing what we want, that fossil record really is scanty, but you would expect to see some
sort of organism sporting a pretty big brain in the fossil record during one of those eras
where intelligence arose. They should have been pretty dominant. We donât really see anything breaking the
general pattern back to that first single-celled life and you would think if aliens had arrived
and colonized, then thereâd be a sudden appearance of stuff that didnât fit. Maybe not, we tend to assume anything we find
does fit, so we could have some freaky alien fossil and just fit it in through determination
and an assumption of what the right answer was by everyone looking at it. Still, it feels a stretch to assume we wouldnât
have at least one fossil that stuck out like a sore thumb, maybe it lacked bilateral symmetry
or such. Nonetheless we do need to acknowledge that
we cannot actually rule out either of two ancient civilization options. First, that large brains can evolve rather
quickly and that one a bit smarter than humans might pop up and get to advanced technology
in only a few thousand years after discovering fire. Remember, humans may have discovered fire
a million years ago, not really very long after we got bigger brains, though thatâs
a bit hard to say, but we did kind of sit on it for 99% of the time we had it. Pottery and metal-working are recent inventions,
having been around for only about the last percent of time weâve had fire for. We used it for warmth, food, safety, and light,
and probably fire-sharpening sticks, but for 99% of the time we had it, that was the extent
of our technology. If weâd been a bit smarter or more numerous,
we may well have gotten pottery within a few hundred years of having fire and it only took
us a handful of millenia with our current brains to get to space from there. Had we been smarter, we may have gotten to
space, and cheap doomsday devices, in under a thousand years. Additionally, we started burying our dead
ritualistically as we got smart enough to realize what death was, and many opted for
burning almost right away. We donât want to rule out civilizations
not leaving fossils because they had burial or body disposal methods that made finding
fossils way less likely, meaning that almost as soon as they got big brains, they almost
entirely disappeared from the record. In alien biology, that might include skulls
that were not solid bone, as an adaptation to allow bigger brain growth, but which decayed
quickly, or that that civilization engaged in ritualized cannibalism, bones and all,
to take in the honored dead, so to speak, or there just happened to be very voracious
critters when it comes to finding and eating bones. In that same context, if weâre suggesting
bigger brains, and talking about civilizations blowing themselves up, one that goes from
making pottery to designing nuclear bombs in a couple centuries might leave a lot less
evidence they were around due to their abridged timeline. If advanced technology almost inevitably kills
off intelligent critters, then the smarter they are, the shorter their dwell time. Second, parallel biology and convergent evolution
canât be ignored, especially for choosing worlds to visit. Again, our fossil record is slim and our connections
for missing links is necessarily hazy, and it wouldnât be hard to have an alien civilization
arrive that had picked Earth because it already had life and life not too different from theirs,
especially in terms of fossil-preserved qualities, like physical shape. I really think thatâs a stretch but thereâs
a number of extinction events where if those had actually been the result of an alien civilization
arising and terraforming our world, we might have missed it simply by assuming it must
be natural and thus connecting the few dots we have under the assumption that was the
case. As a brief tangent, that is always a worry
when we're doing science and why I tend to emphasize the point, in Fermi Paradox phenomena
discussions, that Intelligence is generally going to be blatantly obvious. You can confuse a single crude tool for a
natural object, but not a workshop full of tools and electronics. So too, the ruins of a civilization might
give off subtle telltales that might be harder to differentiate from nature, but a big old
Dyson Swarm actively existing is not going to look any more natural than New York City
does. However, it is a necessary assumption in science,
when looking at the Universe, to greet any new phenomena or bit of evidence as being
natural rather than of intelligent, paranormal or supernatural origin. I donât think thereâs a more valid approach
scientifically, but we do need to be mindful that, just because it gives us the clearest
vision overall, doesnât mean it doesnât blind us sometimes, and we may have built
some houses of cards on some phenomena or evidence by assuming it was natural, and shoehorning
everything in to fit our expectations. The Giantâs Causeway is an example that
comes to mind, all those unusually hexagonal stones, itâs so tempting to assume it is
artificial, much as a hexagonal beehive comb is, but it turns out to be a natural effect. In that same way, if we dug up an actual road
built by some ancient giants, we might trick ourselves into believing it was natural. By that same logic, we might trick ourselves
into seeing some extinction event and shift in biology as a natural extinction and evolution
process, not some alien showing up, or future time travelers, or extra-dimensional entities
or deities. That said, again, probably not. Even where missing links are missing, thereâs
other stuff missing, like higher lifeforms. We can definitely invent a scenario where
that still works of course. Perhaps the aliens came long ago and didnât
believe in colonizing to eradicate existing life, so kept themselves in domes along with
their own organisms, but some of their microbes got out, or a few organisms that resembled
terrestrial ones so much, they didnât notice a few snuck out and didnât send out the
drones to hunt them down. Or they engaged in some hybridization of alien
and terrestrial life. And we donât currently believe we have any
DNA from back then, it could be that our lifeforms native to earth used something different and
their hybrids were using DNA which was alien to Earth originally. Or it really could be that DNA is just the
norm in the Universe and convergent evolution in general is a thing, see our episode on
Convergent Evolution, for more discussion of that. One other option is that civilizations actively
erase themselves, and for instance, a science colony comes to study us, or make us, might
release drones and nanobots to go and clean up any escaped lab samples and erase right
angled ruins and such from the geological record. It also isnât too much of a stretch to assume
a civilization that felt like it really hurt its native world might decide to migrate off
it and restore it to a near-pristine condition, there are trillions of empty worlds to colonize
but only one beloved homeworld, and that could easily involve such erasures while simultaneously
not engaging in too much de-extinction technologies, since resurrecting mammoths and dodos might
be seen as just as bad to the new native ecology, so they just do it on artificial habitats
theyâve moved to or made as nature preserves. Thatâs plausible enough, we can probably
bring mammoths back, but putting them back into our ecology just messes things up again,
so we build a space habitat just for them. It begs the question of what happened to them
of course, these ancient predecessors, but the predecessor extinction path is less tricky
in terms of the Fermi Paradox than the normal non-exclusivity issue of space aliens colonizing
the galaxy, then somehow managing to have all of their colonies die off, so that we
see an empty galaxy even though it has often been colonized by various aliens. Because itâs actually easier for a world
to evolve intelligence twice, after some partial doomsday, than to have two separate worlds
kindle intelligent life independently. So we donât have to assume a galaxy full
of aliens for the Silurian Hypothesis to apply. So what weâre seeing thus far is that we
canât rule it out, which is nice for anyone wanting to write a story about it, but that
it would take some plot conveniences or really contrived scenarios. Not impossible ones though, and given that
I just got done warning everyone about how we might trick ourselves into ignoring such
events by assuming they were natural, those events might seem more contrived to us because
we assume theyâre not real. Reality is also often stranger than fiction
and Iâve lost track of how many times real world events and decisions were truly made
where, if they had been in a film or novel, the audience would have rolled their eyes
at how unbelievable such behavior was. Which goes to the general point of how popular
such theories have been down the years, in and out of fiction. To many of us, they sound interesting but
implausible, good stories. To others they are very believable and while
I strongly disagree, I canât really just dub it crazy conspiracy theories only idiots
believe in, even ignoring that I try not to say that about conspiracy theories in general. Thus, much like the authors of the Silurian
Hypothesis paper, I donât really see any good reasoning to think an ancient civilization
once dwelt on Earth millions of years ago, but thereâs no really good way to eliminate
the possibility entirely and there could be a lot of at least modestly plausible ways
it could have happened and we just missed it. So, of course, the other big question is how
long our ruins would be around and the big issue here is that we have to ask what the
heck erased us, since it would be relevant to how long those ruins would last. If we did program some grey goo designed to
erase all signs of technology, then the answer is not very long at all. And it is possible a civilization aiming for
techno-primitivism, out of fear of the dangers of keeping technology, might contemplate something
like that, possibly to police dangerous technologies and prevent anyone from building them, the
nanobots just seek out and destroy higher tech, and perhaps that eventually runs amok
or the civilization dies off and it eventually kicks over their traces. Otherwise though itâs very hard to imagine
anything wiping us out completely, but leaving life behind that could eventually replace
us, and needs many millions of years to get smart enough to engage in archeology. Give me a doomsday in which even a thousand
people survive and Iâll give you a civilization thatâs back on its feet before our cities
and infrastructure have been covered with vegetation and sediment to hide them. Weâve examined this in detail in our episodes
like: Cyclic Apocalypses and Post-Apocalyptic Civilizations, and you almost need to do something
like infect humans with a retrovirus that makes us fairly dumb, to have us not repopulate
and build pretty quick. Again, I could see that, maybe we decide our
tech is too dangerous and we unleash a virus to dumb us down, but then why are the cities
going away as ruins? I canât really see us deleting the pyramids
and other big stone structures â of which we still make tons today â out of fears
of dangerous technology and runaway AI. Of course, you could just have a super-plague,
something made in a lab, kill off every single human, and then maybe ten million years from
now, chimps, racoons or elephants finally get sapient and technological. And then thereâs all that leftover stuff. Yeah all the electronics are gone though youâre
likely to have buried computers who have suspicious corroded wafers full of semiconductor residue
on them. Got an awful lot of abandoned mines that you
encounter that probably all collapsed or filled with sediment and they are digging through
looking for coal or metal, and call in the geologist who wonders why thereâs a weirdly
uniform corridor of sediment and fill running through geological layers and exploration
finds tons of petrified wood and metal beams holding those tunnels up. The continents move, so the South Pole currently
on Antarctica wonât be in the same place a million years from now. No archaeologists scanning their south pole
would see our old bases buried under the ice there. However, just as H.P. Lovecraft and others set ancient civilizations
to have once lived in Antarctica before it got to the South Pole and got buried under
ice, we need to remember that even 10 million years from now, Earth is going to look noticeably
different, especially if weâre more technologically advanced at that time and really messed around
with our planetâs landscape, building artificial islands and seawalls and other concepts we
explored in the Earth 2.0 series. Nonetheless, I just canât imagine that future
raccoon civilizations wouldnât eventually find some remnant of us somewhere. Of course, even though archeology and paleontology
are explorations of the ancient, theyâre not really all that old of fields themselves. Perhaps given time, we will find the ruins
of some ancient civilization that once dwelt here, and wonder who they were and what happened
to them. That would be an important puzzle to solve
too, since whatever befell them might befall us as well, if weâre not careful. So I mentioned at the start that todayâs
topic gets its name from an episode of Doctor Who way back in the first year of the Third
Doctor, Jon Pertwee, who was on from 1970-1974, and Doctor Who and the Silurians was the second
serial he did for 7 episodes. They and their nominal cousins, the Sea Devils,
who appeared a couple years later on the show, both disappeared from TV for over a decade
before making a reappearance but they did show up in quite a lot of the doctor who novels. As you probably know, classic Doctor Who had
a very long hiatus off TV between Doctors 7 and 9, but there were a lot of books written
during that period along with audio dramas, often set during prior doctors and also often
starring or entirely narrated by the original actor. You also get some lost classics or unproduced
episodes like Shada by Douglas Adams, that eventually became his book Dirk Gentlyâs
Holistic Detective Agency. There are hundreds of Doctor Who Audio Dramas
and Audiobooks out there, including Doctor Who and the Silurians, our Audible Audiobook
of the Month, and they are all available on audible, as are many novels from other amazing
series that got canceled before their time, also often narrated by the original cast members,
so you can continue the journey with them. Audible has thousands of such audiobooks and
dramas available and literally centuries worth of content for you to pick from, and more
being added every day faster than you could listen to all of it. But they donât just have audiobooks, they
also have many excellent podcasts, such as Science & Futurism with Isaac Arthur, where
we have every single episode on Youtube, plus several audio-only exclusives Iâve made
over the years. Thatâs just some of the great content in
the Audible Plus Catalog, which also has sleep & meditation tracks available, as well as
guided fitness programs for getting into shape this summer, and Audible Originalâs like
Impact Winter, from the folks who brought you Pacific Rim and the Walking Dead. The whole Audible Plus Catalog full of free
books and other content, comes as a bonus when you join Audible, in addition to your
usual 1 free audiobook each month and big member discounts on additional ones, and as
always, new members can try Audible for free for the first month, just go to Audible.com/isaac,
or text isaac to 500-500. All right, that wraps us up for today and
weâll be back next month on July 17th for our next Scifi Sunday episode looking at primitive
aliens and how we should interact with them, But between now and then we have plenty of
other episodes, starting this Thursday with Interstellar Probes, where weâll begin our
two-part story of traveling to an anomalous system to investigate it, concluding with
Life as a Planetary Explorer on June 30th. Weâll pause between those two episodes to
look at the concept of Crawl-onizing the Galaxy, how humanity can still settle the stars even
if we are limited to spaceships moving at less than 1% of light speed, and what that
will look like. Weâll also have our livestream Q&A two weeks
from now on Sunday, June 26th. Then it is on to July for a look at Deep Space
Habitats, then Extragalactic Sanctuaries. If you want alerts when those and other episodes
come out, donât forget to subscribe to the channel and hit the notifications bell. And if you enjoyed todayâs episode, and
would like help support future episodes, you can got to our website, IsaacArthur.net, which
weâve recently relaunched new and improved, and check out our donate tab for ways to help,
and all those other options are linked in the episode description, along with our social
media forums like facebook, reddit, and discord, where you can chat with others about todayâs
episode and many other futuristic ideas. Until next time, thanks for watching, and
have a great week!
Hopefully, about a million Dyson swarms in every direction.
I think the most obvious sign of humans still visible hundreds of millions of years later would be fossils. I'm not thinking of humans, or even things humans built. I'm thinking of invasive plants and animals from North America suddenly showing up in New Zealand and vice versa. This at a time when there is no possible land route for eg a North American rat to show up so far away. I think whatever happens to humans, there are enough animals around that some of their fossils would be preserved. Hypothetical far future scientists looking at this fossil record would be very very curious how that happened, and it might be the first/most obvious clue they get to our existence.
Here's what I think will be left of our modern civilization 50 million years from now.
-Grooves in the ground where buildings and roads used to be.
-Microplastic particles
-Fossils of humans and domestic animals
-Areas that should have oil or certain minerals but simply don't
-Casts of trash buried deep in landfills or radioactive isotopes where we buried nuclear waste
-Everything we've ever sent to space that remains in space at that point.
-Genetic code in our descendents
-Traces of our cultures and languages if someone was to backtrack the same way we backtracked to Proto Indo European.