The Silurian Hypothesis

If an advanced civilization existed on earth several million years ago, would we actually be able to detect that they were here? It may sound like conspiracy theorist bait, but a serious and balanced look at the question reveals a lot about geology, climate and the search for alien life. In this episode of the Stuff to Blow Your Mind podcast, Robert and Joe discuss the silurian hypothesis.

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind, the production of
My Heart Radio. Hey, welcome to Stuff to Blow Your Mind.
My name is Robert Lamb, and I'm Joe McCormick. And
today we're going to be talking about a subject that
I've actually had on the radar for a while. This

(00:24):
is something that was making the rounds on science blogs
a few years back, and it has been suggested by
a number of different listeners. So I'm glad we're finally
coming around to it. I think I had some hesitation
for a while that I want to briefly explain right
at the beginning here. But today we're gonna be talking
about an idea known as the Silurian hypothesis. Uh. And

(00:46):
just to give you a little bit of background knowledge,
we spent several minutes before recording today trying to look
up how they pronounced Silurian on Doctor Who, because I
was like, sure they might use some kind of British
English variation where they a Silurian, but but a last
we could not ever get the doctor to say it right.
I watched I think an entire scene where one of

(01:08):
the more recent doctors was chatting with us Silurian or
Silurian out out of your will, and they they it
was like they were trying not to say it, like
if they said it, one would would pop up and
and crawl out of the screen or something they used
they referred to another alien race. There wasn't even in
the scene, and I don't even think was part of
that episode. And then in all these other terms. But yeah,

(01:31):
they were just trying to mess with me. So this
is a topic that I have been interested in covering
for quite a while. It's it's been a few years now,
But Rob, when you suggested it, I realized that I'd
always been hesitating and not wanting to quite go ahead
with it. And I think I realized the reason for that,
which is that when I saw people mentioning this paper

(01:52):
on the internet, it was clear to me that a
lot of them were getting exactly the wrong takeaway from it,
Like they were matching onto a very shallow understanding of
the concept and and running off in a in a
very different direction than the authors intended. Not only a
different direction than they intend, but a direction they specifically

(02:13):
say do not go in, and specifically say that they
are not trying to to make Yeah. Uh, so to
to clarify what we're talking about here. The Silurian Hypothesis
paper begins with a fascinating question, in the words of
the author's quote, if an industrial civilization had existed on
Earth many millions of years prior to our own era,

(02:36):
what traces would it have left and would they be
detectable today? That that's the question at the heart of
this paper. And obviously this is a tantalizing premise. You know,
it sets your mind racing with images of impossibly weird organisms,
you know, like land dwelling octopi and stuff in the
in their own weird cities, and and what kind of

(02:57):
technology would they have? Things that are as alien as
anything you could imagine on another planet, except they would
have all been from here, native to planet Earth, dating
back millions of years into prehistory. But while this is
a really attractive imaginative exercise, I think the first order
of business when talking about this subject is to be

(03:19):
clear that the Silurian Hypothesis paper is about coming up
with a framework for detecting physical traces of industrial civilizations
and understanding how long those traces last. So it's about
trying to say, what are the right questions to ask
when you're when you're looking at a planet and saying,
how could we tell if there had been a civilization

(03:40):
on this planet a long time ago? It is not
a paper arguing that there was in fact a lost
civilization deep in Earth's past. So it's not evidence for
lizard men, ancient aliens, Graham Hancock, junk Atlantis, or any
of that stuff. But I would say in its true form,
it is a really interesting question. Yeah, And at heart

(04:04):
this episode is is not going to be about scientific
evidence for lizard men civilizations in the Hollow Earth. So
if you're looking for that, this is this is not
the episode for you. But yeah, what I love about
it is that it takes this sort of fantastic idea
and then examines it reasonably, and that examination eliminates some
very interesting geologic, climatic, and astrophysical considerations, So you know,

(04:25):
setting aside pseudoscience and pseudo archaeology here. But on the
other hand, I think if you if you're looking for
some sci fi fund this topic in this episode will
also still engage you. Um, but it is interesting how
from a certain perspective you can imagine people being drawn
into it by just sort of this sci fi idea,

(04:46):
this idea that does lean lend itself well to sort
of conspiracy theorist mindsets, and then realizing, actually, this paper
is about geology and UH and U and the last
year of our planet and also, oh, I guess kind
of you know, in many cases, kind of a downbeat
message about the lasting impact of human technology on our planet.

(05:10):
And on the other hand, too, how forgettable we may
be from the standpoint of geological history. Yeah, so if
you're on board for all of that, you've come to
the right place. So real quick, I do want to
just discuss the Doctor Who reference here, since since uh,
the authors Schmidt and Frank took the name for the

(05:31):
hypothesis from the Doctor Who species the Silurians, who first
popped up in the nineteen seventies series Doctor Who. And
these Silurians, I think, now you've got me saying silurians,
I probably probably stuff this way. Well, it gets even
worse because so they take the name of the hypothesis
from this Doctor Who series where these creatures show up.

(05:54):
But then they say explicitly in the paper, you know,
the range we would really be looking at would actually
be after the Lurian geologic period, the Silurian period is
something that's like a roughly twenty million year period that's
more than four hundred million years ago. I don't remember.
It's like four hundred and forty something to four hundred
and twenty something, I think roughly. But if you were

(06:15):
seriously looking for evidence of lost civilizations in Earth's ancient past,
you'd probably be looking for things like after about four
hundred million years ago, coming you know, forward in time
from the Devonian period, when you could have the reasonable
biological basis for land dwelling animals that might have evolved
complex technological intelligence. Yes, but any rate. In Doctor Who,

(06:39):
especially in that original nineteen seventy uh appearance, the Silurians
are these kind of lizard men um. They factor into
this plot with the third Doctor played by John part
Way Who nineteen nine, nine ninety six, and then they
subsequently pop up again with the fifth Doctor played by
Peter Davison and the eleventh Doctor played by Matt Smith,

(07:00):
and then more recently the third teenth Doctor played by
Jody Whittaker. So this is just the TV show. I
can't speak to the various books and audio dramas that
have come out, and their look has changed throughout the film. Um,
you know, they are, in essence, this cold blooded, prehistoric
reptile like species with significant technological advancement that they they
I think they end up entering various states of suspended

(07:22):
animation to avoid uh you know, major changes on Earth,
changes to the climate, etcetera. Um, and then they re
emerge and encounter the Doctor. Um. So yeah, they're They're
one of the many interesting alien and otherworldly species that
pop up. Uh. Though, I guess with the Silurians, one
of the key things is that they're they're not pure aliens.

(07:46):
They're they're sort of the originals. There are their original terrans,
original earthlings, uh, that are then encountered by these evolved
apes that come much later. I mean to to them,
we are the aliens. Yeah right, we're these weird future creatures. Uh.
The image would tend And I gotta be honest, I'm
not a hoovoid, so I don't know the lore. But

(08:09):
the picture you're showing me of the Silurians, they look
like they look like if the world was all creature
from the Black Lagoon and there was a leather face
of the creature from the Black Lagoon civilization. Yeah, I
mean they're definitely Doctor Who creatures of this era, which
which I tend to love these costumes. I know they

(08:30):
were working with with with with budget limitations here, but yeah,
the the aliens and robots of this era really really
called me. Now you said you look kind of fish like.
Bear in mind, and I'm sure some Doctor Who listeners
Doctor Who viewers will will will chime in here, But
I believe they are related to another species that pops
up on the show that live in the water. I

(08:50):
think they're like the sea devils or something. Um, but
these guys are not aquatic in nature. I think I
got that right. The seed of Oh wait, this is
that like a a bunch of intelligent euryptorids or something
something like that. Yeah, alright, So this is two thousand
eighteen paper the Silurian hypothesis, Would it be possible to

(09:10):
detect an industrial civilization in the Geological Record? This was
published in the journal International Journal of Astrobiology. UH. It
draws its name from that Doctor Who episode, and the
authors here that they point out that they may be
the first to seriously consider whether a technologically advanced civilization
could have evolved prior to Homo sapiens on Earth, though

(09:32):
the authors due stress that this is a to the
best of their knowledge situation, so you know, it's entirely
possible somebody was batting around the idea previously, but this
may be the first, and certainly this was. This one
really made a splash when it came out. Okay, So
the two authors here would be Adam Frank and Givin A.
Schmidt right and Frank is a is a physicist and astronomer,

(09:54):
and Schmidt is a climate scientist right right. Schmidt is
a climatologist, climate model and director of the NASA Gotted
Institute for Space Studies in New York and co founder
of the award winning climate science blog Real Climate. Frank
is a physicist, astronomer, and writer whose work has appeared
in such publications as The New York Times and NPR,
and I believe we've actually referenced his work on the

(10:15):
podcast before. Uh. He also has a book. He has
a few books, including The Constant Fire, The End of
the Beginning, and Light of the Stars. Those are all
nonfiction science books, of course, So to be clear, we're
talking about two very legitimate scientists and science communicators, not
you know, not a couple of of quacks who were
staring into the hollow Earth or anything. So the authors

(10:38):
here begin with a very reasonable consideration of the search
for intelligent life elsewhere in the universe. Uh. And then
this is something we've we've touched on the show plenty
of times before. Ours is the only model of life,
but we generally consider technological advancement to be a hallmark
of intelligent life. And more to the point, something we
can search for signs of, uh concerning other worlds and

(10:59):
other star systems. Uh. You know, and anytime you can,
you can figure out how to look for signs of
of advanced and expansive energy harvesting or consumption. Uh. That
might be a way for us to tell if there's
something else out there that is significantly advanced. Right, and
it also might be a simple prerequisite for contact, because uh,

(11:21):
they're talking about so that they started off by looking
at this as an astrobiology question. You know, you're you're
looking for signs of life elsewhere in the universe. And
of course, the the search for intelligent life in the
universe in practical terms, what's accessible to us really boils
down to the search for life capable of Harvard harnessing
radio technology within our galaxy. You know, you could probably

(11:42):
find maybe chemical biosignatures in in the atmospheres of exoplanets
that would give you an indication that there's some kind
of life there, maybe bacterial in nature or whatever. But
if you're looking for intelligent life, you're you're probably talking
about radio of some kind, right, And so the kinds
of civilizations that develop radio communication technology would fall under

(12:04):
the classification of industrial civilizations. And these are what author
the authors define as civilizations that have the ability to
harness energy on a global scale. And they bring up
how this actually feeds into one of the the recurring
characters in in the astrobiology literature, the Drake equation. That's right, Yeah,

(12:24):
they bust out the Drake equation, and of course consider
how how some of the takeaways relate to Earth, especially
the notion that over the course of a planet's existence,
multiple industrial civilizations can theoretically arise over the span of
time that life exists there. And then we have to
factor in questions over you know, how many times life
itself may have evolved or started out on Earth before

(12:46):
our last universal common ancestors got going. The possibility of
a shadow biosphere and the idea that species like dolphins
may suggest independent evolutions of intelligence on Earth. Um, you know,
so we're left with this idea that, yeah, the radically
and given the footprint of life on Earth, you could
have had multiple intelligences uh evolved and arise during that

(13:08):
time period. Because that's certainly what the Drake equation seems
to allow for concerning other worlds. Well, yeah, and I
you know so I kind of love the Drake equation.
You know, it's a famous tool that I really enjoy
thinking about because because it does the job of taking
a question that seems like we could not possibly answer.

(13:29):
The question is how many active technological civilizations are there
in the Milky Way galaxy? And you know, if you're
being honest with yourself, the correct answer to that is
how the hell should I know? Like, there's no way
to answer that question at all. But what the Drake
equation does is break that unanswerable question down into a

(13:49):
number of other questions that you then multiplied together to
get an estimated number. And many of those smaller questions
themselves could perhaps be answered, and in fact, some of
them have been answered since the Drake equation was first formulated.
Uh so, So it decomposes an unsolvable problem of are
there aliens out there? And if so, how many, into

(14:11):
a series of smaller problems, at least some of which
are solvable, maybe all of which are. You know, you
could come up with some kind of reasonable gas about.
And so the classic formulation of the Drake equation is
to get your number of civilizations in the milky way,
you would multiply a bunch of different terms together. So
one is the rate of average the average rate of
star formation. You know, how much do you get stars

(14:34):
times the fraction of stars that have planets times the
average number of planets per star, times the fraction of
planets that develop life times the portion of those life
systems that gain intelligence, times the portion of those intelligent
life systems that develop technological means to communicate times. And

(14:56):
then here's a really interesting term, quote the length of
time l over which such civilizations released detectable signals. And
it's this very last term that I think very often
gets overlooked by people who are thinking about, you know,
are there aliens out there? And how could we know?
I think we often tend to assume that, well, once
there are aliens with technological means to communicate. That's just

(15:18):
like a you know, progress only extends from their civilizations
just continue to get bigger and their capabilities expand and
they spread out from there. But I don't know that
there could be severe limitations on the length of a
radio receptive or radio broadcasting civilization. Maybe they only exist
for a few hundred years. Because one thing we know

(15:39):
is that our technological civilization is just a tiny blip
on the history of planet Earth, even a tiny blip
on the history of life on planet Earth. Earth is
four point five billion years old. There's been life on
Earth for most of that time. Uh. The authors here
estimate that there has been complex life on Earth to

(16:00):
land surface for only about four hundred million years. So
that's only a fraction of the entire history of Earth.
But that but four hundred million years is still a
gargantuan amount of time compared to the length of human civilization.
They say, industrial civilization, you know, by their metric, has
probably existed for only about three hundred years. This is
since roughly the beginning of mass production methods for for things,

(16:24):
and so if humans were wiped out by a global
mass extinction, of some kind in the near future. Our
industrial civilization would just be this tiny little splinter, this
blip of three hundred years on a history of a
currently four point five billion year old planet. Yeah, and
so from there we get into the question, Okay, if

(16:45):
if you have an industrial civilization like this, it is
just a blip, would we be able to see it?
And if we could see it, what would we look for?
And this is you know, this is pretty much the
meat of the paper here analyzing this sort of question,
which which is great because it it again it gets
into sort of uh, you know, sci fi friendly concepts.
It's a useful in considering the evolution of life and

(17:08):
the existence of intelligent life on other worlds. And it
also shines a light on what we're doing now and
where we are. And and I think also, uh, you know,
illustrates nicely illustrates this idea that um that that the
technology is not just this um that this this this
ramp to Star Trek, you know, or this ramp to

(17:30):
the culture or any of our more optimistic sci fi
dreams like there are there are severe challenges. Uh. And
of course there's there's always the risk of extinction. That's
exactly right. And one thing that's funny is we don't
know whether the rise of technological civilization should generally be
understood as, on average, a linear process where it just

(17:53):
sort of goes in one direction and keeps going in
that direction, or whether it should be understood as on
average a sick clickal process where you get a rise
in technological civilization, then then it disappears for some reason.
You can imagine what some of those reasons might be. Um,
and uh, and then maybe rises again out of the
out of the same biosphere. I mean, either one I

(18:14):
think is a perfectly plausible model to entertain is like
what usually happens in the universe. Uh. And we just
don't have the h we don't have the evidence to
really have an opinion on that. Yeah, I mean a
lot of it just comes back to the fact that, again,
we are the only model of intelligent life, and certainly
technologically advanced intelligent life that we have to look at,

(18:38):
So we have nothing to compare us to. Yeah, and
we don't know what's going to happen to us in
the long run. Right. So uh, Well, let's get into
the I guess the sort of the first part of
the paper, and I do want to drive home that
if you want to just go right to the paper
yourself and dive in. Um, you just do a search
for the title and you can find it hosted on NASA.

(18:59):
They have as has a as a PDF of this
that's very easily accessible. Uh. You can also read it
in full on the Cambridge University Press website, which I
think is the press behind the journal, the International Journal
Journal of Astrobiology. And yeah, so it's all on their
end with the references hyper linked and all that, which
is nice. Yes, yeah, absolutely so if he hit a paywall,
don't don't give up. It's out there. UM. And I

(19:21):
believe Adam Frank also wrote a piece for What the
Atlantic where he nicely summarizes some of the ideas here.
Oh yeah, and he also tells a funny story about
how they arrived at writing the paper, because I think
he says, uh, he showed up in Gevin Schmidt's office
to to talk about UM, to talk more about astrobiology
like Drake equation type questions, and he's like, okay, so

(19:42):
we we we know we've got one industrial civilization on Earth.
And then Schmidt responded by saying, how do we know
we're the only one just hitting that early like wall.
They're like wow, And then that turned into the paper. Yeah,
and it's it's it's quite a paper. So let's see,

(20:04):
let's get into the first part of it, which I
think you can loosely think of it's just sort of
a look at the limits of our vision. So they
point out that for the last two point five million years, uh,
there's widespread physical evidence of things like climate change, soil
horizons this is where one layer of soil differs from
belower above, speaking to changes recorded in the soil, as

(20:27):
well as archaeological evidence of non Homo sapiens cultures such
as the Neanderthals. And this two point five million year
period is known as the Quaternary. Now, going back before
the Quaternary again more than two point five million years ago,
the land evidence is harder to come by. You have
to depend on drilling, mining, and occasional exposed sections of

(20:50):
the earth. Even in the ocean, sentiment evidence apparently only
goes back to around one seventy million years ago. Yeah,
and I think for me this was actually one of
the most interesting parts of the paper because I would say,
if you just go by standard intuition. A person might think, uh,
you know, if there had been a civilization on Earth,

(21:12):
you know, a two million years ago or something like that. Uh,
would wouldn't that just be completely obvious, Like we'd see
evidence of it all around us? Would there be ruins
and all that, you know, their their stone hinges, their
skyscrapers and everything like that. Actually it's not. It might
not be as obvious as you might think. In fact,
the evidence of it could be rather scarce. And this

(21:34):
runs counter to our sci fi imaginings, right, because you
encounter elder civilizations and in other works like there's usually
some sort of a ruin or a vault or some
sort of mysterious monolith or something like the idea that
the elders would just be gone entirely, like just erased,
not by some sort of a conspiracy or by some

(21:55):
sort of a you know, alien shenanigans, but just because
things don't last that long. That's uh, it's an alien
concept from too many of our again, too many of
our creative visions of of what the future. In the past,
maybe exactly so, we think, well, you know, there are
ruins of civilizations from thousands of years ago, but that's
thousands of years ago. That's nothing in geological time. The

(22:15):
surface of the I mean, look a look at what
a map of the land formations on Earth just you know,
sixty million years ago looked like It's like, you know,
the the surface of the Earth is not fixed and constant.
This is a geologically active planet. So would there be
ruins all around us? Would evidence of a civilization from
hundreds of millions of years ago just be totally obvious?

(22:38):
I think I probably by the answer that the authors
give here, which is that no, it would probably not
be totally obvious. In fact, it might be incredibly difficult
to find evidence of at all. Uh. And so one
of the the interesting points the authors make here is
that the the exposed land surface of Earth, of course,
is geologically very young on average. They cite evidence from

(22:59):
a study by ma at mon at All in two
thousand nine that the oldest large patch of land surface
on Earth is probably in the Negev Desert, and that's
only about one point eight million years old. One point
eight million years, I mean, compared to the history of
civilization is a long time. But that's again, it's like
nothing in geological time. It's a tiny fraction of of

(23:19):
earth history. So if we wanted to find remnants of
a civilization from say, hundreds of millions of years ago,
you probably would not find that on the surface of
the Earth. You'd have to look for it in in
exposed geological strata from from previous eras. And even then
you can't just count on the fact that you would
be finding fossils of that civilization all over the place. Yeah, exactly.

(23:43):
That They that they hit on something we we've discussed
on the show before, which is, of course that the
fossil record is inherently incomplete, because fossilization only occurs when
conditions are just right. Um. They point out that that
of all the dinosaurs that ever lived, and there were
a ton of you know, uh, you know, they're the

(24:03):
era of the dinosaurs taken as as one gigantic, gigantic
monolith just dwarfs anything that that that that humanity has
ever occupied. Uh. You know, it is a it is
a cathedral, and and we're we're not even like a
child's dollhouse, uh sort of situation here. Um. So uh,
you know, out of out of all of those dinosaurs

(24:25):
that ever lived, there are only a few thousand near
complete specimens. And so the authors here contend that given
the rarity of fossilization, a species is short lived, as
Homo sapiens might not make it into the fossil record
at all. And of course, for fossilization to mean anything
to us, or to you know, anybody who's doing a
uh doing you know, some sort of an investigation of

(24:46):
a planet or our planet, those fossilizations would have to
survive and then they would have to be found. Yeah, exactly.
And and so again this might be pushing against your intuition.
You would say, like, wait a minute, there's there's there's
there's signs of human life all over the surface of Earth.
And and we have, you know, at least a few
thousand uh complete dinosaur fossils, enough to have museums of

(25:07):
natural history with dinosaur fossils in places all over the world. Uh,
surely you'd expect more. But dinosaurs existed for almost two
hundred million years. Human civilization again is like it's a
few thousand years at this point. Yeah. So the problem
here is like we have trouble comparing the odds because

(25:28):
you're not realizing how many millions of times more the
dinosaur bodies got to roll the dice than ours would. Yeah. Absolutely.
Another thing they touch on is that is the example
of technology. Uh, and they point out how rarely complex
early examples of human technology are ever found. So if
you're thinking, well, surely we would find one of these

(25:50):
factories or something that was made by one of these
factories that a previous civilization might have had, well not necessarily. Yeah,
sure surely my rice cooker would be found hundreds of
millions of years in the future. But yeah, that they
mentioned several reasons why that's maybe not as clear as
you might assume. So they say urbanization that currently represents

(26:13):
less than one percent of the Earth's surface, So that's
a limitation on the deposition side of of creating a
fossil record of our current civilization. Only small parts of
Earth's surface are actually inhabited by humans. That that sounds counterintuitive,
but it's true. And then they point out that quote
exposed sections and drilling sites for pre quaternary surfaces are

(26:35):
orders of magnitude less as fractions of the original surface.
So human civilization currently only feels a small portion of
Earth's surface right now, and we only access tiny fractions
of Earth's previous surface through through various kinds of drilling
and you know, access through exposure to rock strata. So

(26:56):
there's just like extreme selection filters on both sides, on
the deposition and on the excavation side. Yeah, it would
be kind of like even if you you knew somehow,
with some certainty that there was that that there was
a technological civilization during this time in the ancient ancient past. Uh, yeah,
you would. You would have to you have to really

(27:17):
know exactly where to drill down to hit them. You
couldn't just expect to randomly do it unless you did
a lot of drilling and digging and and excavation. Um.
But but but so what we've been talking about here
is challenging the the intuition that you would just be
finding physical fossil remnants and artifacts of this civilization from

(27:40):
hundreds of millions of years ago all over the place.
And I think they do a very good job of
knocking that down. But of course it is not hopeless
because they say, while our chance of finding the physical
remains of a hypothetical Silarian civilization might be very low,
there would be other traces of the existence of that
civilization that would be preserved in the geologic record, and

(28:00):
you you would have a very good chance of finding
those traces. Yeah, and that's that's what most of the
rest of the paper deals with. I do want to
point out one of the things that they bring up
in passing that I thought was interesting. They point out
that that you could certainly make an argument for or
against the evolution of intelligent life in a world based
on the probable evolution of species that are in the

(28:21):
fossil record, but that they would be focusing on physiochemical
tracers for previous industrial civilization. So I hadn't really thought
about this, but like the idea of like looking at say,
dinosaur fossils and saying, well, we don't have evidence that
they evolved in into an intelligent technological species, but if

(28:43):
we but we can make an argument based on this
fossil and this fosil fossil that they were headed in
that direction. I feel like even that's the kind of
thing that probably wouldn't be quite as clear as your
intuition might lead you to assign them, because I mean,
like intelligence in mammals arose very rapidly in geologic time. Yeah,
So again it reached this situation where the fossil record

(29:05):
could just be missing that snapshot entirely. So this all
leads you the next to the next major question. Given
the limits of what we can dettacked in the geochemical record,
what exactly could we look for on a planet to
see if an industrial society ever existed there? And yeah,
that's what the bulk of the paper focuses on. So
in the case of Earth, if an organized, intelligent society

(29:27):
evolved during the pre Quaternary time but they didn't reach
the level of an industrial society, there simply would be
no record of them as far as this paper is concerned.
Right there, they're looking for the kinds of chemical, material
and climate type changes that would leave a trace in
the geologic record, and that would primarily be a function

(29:48):
of of industry, basically of energy, production of of material
working things like metals and plastics, and the uh and
the methods of harn using energy for industrial use. I
was reminded of our episodes on fire technology because if
listeners may remember, we discussed, well, could something that evolved

(30:11):
in the water or or on a water world, could
they ever really get any kind of advanced technology going
if they didn't have access to the surface, and that
seems to be a factor here as well, as they're
only looking at the period during which something could have
evolved on land. Yeah, so you could maybe have advanced
intelligence in the water. But it's maybe this is just

(30:31):
a lack of imagination on our part. You know, you
always need to be aware of the limitations of your vision.
But it does seem hard to imagine advanced technology under
the water, because like if you don't have fire, you
can't do metal working, or metal working is very difficult.
I don't I don't know. It just seems harder to
imagine how technology like we understand it could come about
in the water. But again, you know, limits of our vision. Yeah,

(30:54):
so they say, quote, the focus is thus on the
period between the emergence of complex life on land in
the Devonian four million years ago in the Paleozoic era
and the mid appli A scene. Uh, and that's around
four million years ago, Yeah, because if it was much
more recent, you'd you'd probably get into the area where
you'd start to expect to actually see those kinds of

(31:15):
remnants and artifacts that that we were talking about. Right,
So they get into the discussion of what we might
look for, and they haven't nicely divided up. The first
one is, uh, well, they basically have two broad categories
and then some some details on that category. The first
big one though, would be looking at the geological footprint

(31:36):
of the anthroposcene. So, as we've discussed in the show before,
there's an argument to be made that the impact of
human civilization on the environment and the geologic record constitutes
its own geologic era, the Anthropocene. So not all the
changes would be recognizable millions of years later, but some
would be. Right. So, human activity at this point is

(31:56):
is large scale enough that we are making change is
to the earth that that are that are widespread or
you could even say global, And I was gonna say permanent,
not permanent, but extremely long lived. You know, going way
into the future, you will be able to find signs
in the rocks and the ice and the setiment, you know,
the things on Earth that persists over long periods of

(32:19):
time that will leave records of what we did to
the earth in just the past three years or so. Right,
And uh, And as we've probably mentioned before, the anthropasyn
is not a an official geological era as much as
any of these things can be, you know, official if
it seems like when you're talking about geologic terms, it's
even more ridiculous. We can consider such a small part

(32:42):
of geologic history that we occupy, but there's a lot
of compelling evidence for it, and you often see it discussed,
especially when we're talking about the changes that that humans
have made to the planet and are still making to
the planet and how they may show up in the
geologic record. And just to be super clear, the majority
any of the changes we're talking about of this kind

(33:02):
would not be changes like physical alterations of the Earth's surface.
We're not talking about like records of people digging holes
and building stuff. We're talking about records of like changes
to the to the level of different carbon isotopes in
in geological strata and things like that. Right now, they
also hit upon something that that I thought was really

(33:24):
interesting and in a way almost almost encouraging, uh, the
sustainability paradox. So the idea here is that of course
the longer human civilization lasts, especially technological civilization, the greater
the geologic signal of its impact. Again, that that lasting
those lasting signs in the environment, not the faces they

(33:44):
carved into the mountains but impacts again on their their
geochemical and nature. Um, so that signal increases. But the
longer human civilization lasts, the more sustainable it must become
in order to revive. And this is of course the
reality we're living in right now. If a civilization survives

(34:05):
this test and becomes more sustainable, then that signal grows weaker. Right.
So it's almost like the strength of the signal left
for future people to discover is directly proportional to how
suicidal that civilization is, right Like, the more it is
just burning through fossil fuel resources and the rate of that,

(34:25):
the stronger the signal will be. And so a civilization
at some point, they say, well, will naturally tend to
attenuate for a couple of reasons. Either it realizes it
can't keep going at that rate, or it's going to
cause climate damage to itself, so it will naturally switch
to more sustainable uh energy sources that are harder to
detect in the future, or it of course does so

(34:48):
much damage to itself that it's signal naturally is reduced,
right right. So, so basically coming back to what you
said earlier, it's not just that there there's gonna be
a sign. There's gonna be the signal, uh, this footprint
of a civilized ation, uh in the in the you know,
the geochemical record. It's it's also that it may just
be very short. It may be a little it's not
going to be this. Uh, it's not gonna be a symphony.

(35:09):
It's going to maybe be a note or two. So basically,
the idea being that that that a real strong, much
stronger argument for aliens existing and having some sort of
role or some sort of advanced technology having some sort
of role on Earth in the in the ancient history
would not be look at the pyramids, I think aliens
did this, or I think, you know, ancient scientists did this.

(35:33):
It would be pointing at say a blip in uh,
you know, or an increase in global temperatures during a
certain period of time and saying, I think the aliens
did this, or I think the advanced technology in question
did this. I mean, even then, I think that would
be a very speculative and and difficult to prove hypothesis.
It would be kind of just like unfalsifiable speculation, but

(35:55):
that that would perhaps be the more likely type of
signal you would find if there had been alien intervention,
then you know specific artifacts than all right, well, let's
get into some of the specifics of the footprint that
the authors lay out here. The first one is a

(36:17):
stable isotope anomalies of carbon, oxygen, hydrogen, and nitrogen. And
this is one of the big ones, an estimated point
five trillion tons of fossil carbon via the burning of
fossil fuels and warming of the planet. Um they quote,
we we expect this temperature rise to be detectable and
surface ocean uh carbonates, notably for Manifera. This is a

(36:40):
single celled organism with with with a chalky shell. UM.
Organic biomarkers cave records, such such as stalactites, lake ostracods.
These are minute aquatic crustaceans and high latitude ice cores,
though only the first two of these will be a
retrievable in the time scales considered here. Right, So this

(37:03):
thing about the the isotope anomalies of of carbon and
these other elements is very interesting. So they say, you know,
there are natural distributions that you would find records of
in the different isotopes of carbon that are that are
moving around in Earth's atmosphere. But when people suddenly start
pulling huge amounts of fossil carbon, carbon of a biological

(37:25):
origin out of the ground and burning it, you suddenly
start throwing those isotopes out of whack, and that will
be something that will leave records for millions of years
to come. So you you can look in the geological records,
you know, the record of of strata from previous eras,
and say, huh, for some reason, in this one period
deep in history, suddenly the carbon isotopes got way out

(37:47):
of whack, as if suddenly a bunch of fossil carbon
like coal or oil or whatever had been burned at
a at a hideous rate into the atmosphere. Right. And
so you know, looking at our our time now of
of of modern human civilization, you know this that we
have this fossil fuel consumption, and we have the invention
of the haber Bosch process and the large scale use

(38:09):
of of nitrogenous fertilizers and agriculture, which will also heavily
impact the planet's nitrogen cycling. Yeah, the haber Bosch process. Yeah,
as part of the changes in the nitrogen cycle that
have come about as a result of of industrial civilization
as well, they also touched on sediment to logical records.
The key causes here would be major soil erosion brought

(38:32):
on by agriculture, but also by agriculture related deforestation. Um. Now,
this would be partially mitigated by dams, they point out,
but erosion is also heightened by climate changes and thawing
perma frost. Also sediment content changes due to just industrialization
in general. Uh. Now, here's a Here's another big one

(38:53):
that I think will be pretty obvious. Faunnel radiation and extinctions. Um. Basically,
humans have brought about many extinct actions already, and we're
living in the midst of an extinction event. Uh. This
will likely register in the fossil record. Yeah. Now, of course,
previous major extinction events have usually been chalked up to
two natural things like uh oh, we can track massive

(39:17):
vulcanism as as the cause of this one, or say
a large space impact like the Kti extinction event. But
there are other extinction events in Earth's history where the
cause is not totally clear. You know, there are some speculations,
but we don't know exactly why. Suddenly, it seemed like
there was a great reduction in marine biodiversity at this
point in history. All right. The next area is non

(39:40):
naturally occurring synthetics, so non naturally occurring chemicals generated by
industrial activity that persists in the environment. Things persistent organic pollutants,
chlorofluoral carbons, in related compounds. And they also point out
that steroids, leaf waxes, alkanones, and lipids can be preserved
in sediment for many millions of years. Now, that one

(40:01):
naturally makes me think of King plastic baby. Yeah, yeah,
And that's that's the next thing that they mentioned. And
this one's you know, this one's disheartening but obvious. We've
created tons of plastics, tons upon tons upon tons of plastics,
and they sadly persist not only in heaps and floating masses,
but inside the bodies of organisms, including ourselves, uh so quote.

(40:24):
The potential for very long term persistence and detectability is high. Now,
one of the things they point out about plastic that's
interesting is that plastics may well prove to be a
very long term signature of human civilization and the geologic
record for you know, millions and millions of years to come.
But the development of plastic is also something they would
class under the I don't remember the umbrella term they

(40:46):
use for this sort of chemical contingencies. A technological civilization
does not have to use plastics. Plastics are just something
that humans happen to use. There are other things that
seem probably more universal, like almost any industrial civilization you
would expect to burn lots of fossil fuels. But plastics,

(41:07):
that's more of a question mark. Is that unusual that
we did it, or is that a very common thing
that the civilizations would do all right. The next area
that they highlight transuranic elements. These are elements having a
higher atomic number than uranium, which is ninety two. Most
radioactive isotopes created via nuclear energy or weaponry have long

(41:31):
half lives, but not long enough to be a factor
on the time scale that they're talking about here. But
the exceptions are plutonium to forty four and M curium
two forty seven, So plutonium has a half life of
eight point eight million years, and curium in this case,
we're talking about a half life of fifteen million years.
So in sufficient quantities of disposal, these would these would

(41:54):
pop up. And plutonium has no known natural causes outside
of an actual bernova or something like that. This isotope
of plutonium. Yes, this particular yea plutonium two forty four
so um. So yeah, if you found enough of this
uh in the geologic record, that would be a sign
that's that something was at work, there was some sort
of technological atomic uh enterprise that was in place. Now,

(42:20):
I guess we've already mentioned earlier that the authors are
not going to claim that there was in fact a
a long lost civilization hundreds of millions of years ago.
But they do actually look at the geologic record to say,
are there anythings that that match these criteria we've been
looking at, And they do find some interesting partial matches

(42:42):
that though of course nothing really comes close to evidence
that would be conclusive that there actually was a civilization,
but some of these matches raise interesting questions of their own. Yeah,
they don't look at everything, and they point out that
things like the KT extinction event, we know that that
was not an industrial accident or anything, um and uh.
And and again they're not arguing that these are evidence

(43:03):
of past pre human industrial civilizations on Earth, but merely
point to them as the sources of events we might
look at. Yeah, and I would say the biggest one
that they focus on in the paper is the event
known as the Paleocene Eocene Thermal Maximum or p E
t M. Yeah. This is an abrupt spike in carbon
and oxygen isotopes near the Paleocene Eocene transition uh fifty

(43:27):
six million years ago, resulting in a five to eight
degree celsius global average temperature rise. This is widely thought
to be due to well, I think they're there are
different theories of One is that it's volcanic activity, um.
But there have also been hypotheses put forth that it
could have been a common impact. It could be due
to burning pete methane being released, and a few other candidates. Um.

(43:52):
It's also used as a means of of understanding and
kind of like kind of modeling out the effects of
climate change during our own era. Yeah. And and one
of the reasons this one gets singled out is, uh
so it really looks like, Okay, here we're seeing, for example,
these carbon isotope signature changes that would signal that huge
amounts of biogenic carbon carbon that originally came from life forms,

(44:15):
like the stuff you would find in fossil fuels, is
being burned and released into the atmosphere. Now, how would
that happen if if if it wasn't creatures from the
Black Lagoon with leather face masks digging up a bunch
of fossil fuels and burning them for their civilization. Well, no,
you probably don't need to jump to that conclusion, because
there are other solutions on offer, like, for example, there

(44:37):
might have somehow been lots of access of volcanic magma
two beds of fossil fuels. Maybe certain types of volcanic
activity tended to set a light to a lot of
natural reserves of fossil fuels and shale beds and things
like that. And this almost acted as if the Earth itself,
we're we're setting off an industrial revolution, but it was

(44:59):
just volcano interacting with with these reservoirs of carbon in
the ground. Yeah, all you need is geologic upheaval and
volcanic activity. And again um our our planet has a
as a as a very active geological life, so there's
plenty of opportunity for this sort of thing to potentially
have taken place. So it kind of comes back to
a problem with the signal here, the signal you would

(45:21):
be looking for in the geochemical record, in many cases,
the very sort of signal we're looking for especially concerning
carbon and warming, could have also been caused by these
naturally occurring causes, and so strong signals might be coming
from something else, and more specific signals that we might
look to just might be too weak to to ever
possibly observe or to really make much out of. Oh yeah,

(45:42):
this is an interesting paradox they talk about in their
conclusion of all of the criteria they're able to come
up with in this framework for for looking for past
industrial civilizations, the stuff that you would expect any industrial
civilization to do also has other explanations, and so so
it's not conclusive that it was an industrial civilization that

(46:04):
this would be things like, you know, the carbon stuff. Meanwhile,
the stuff that would be really strong evidence of of
an intelligent civilization origin, that stuff that civilizations might not do.
It's more contingent things like plastics and stuff. You know,
you could have a civilization without plastics. That's not a
necessary milestone in the in the progress of energy harnessing,

(46:27):
and maybe it's even the sort of thing, uh, an
advance civilization would move away from. Coming back to that
the sustainability paradox, when one could hope, I imagine now
the authors again they're very clear about just how far
you should take this hypothesis, stating that quote the Silarian
hypothesis cannot be regarded as likely merely because no other

(46:48):
valid idea presents itself. Uh So they admit that this
this sort of thing could easily get out of hand
with folks pointing to any sort of signal in the
geochemical record as being possible proof of human technological societies.
If you're doing that, you're you're really taking it and
running with in the wrong direction. Yeah, I guess that's
one of the frustrating things about about interesting work of

(47:10):
this kind is so you can point out a lot
of the ways that it's difficult to rule out past civilizations.
But then for a lot of people who just want
to have a theory that changes everything, you know, for
a lot it's just like it's fun to believe that.
So a lot of people just want to believe it.
I want to believe, you know, that there was an
Atlantis mother civilization that birthed everything, or I want to

(47:34):
believe that there were aliens on Earth before humans or
anything like that, because that would change everything, and it
feels so cool to believe it. Therefore, becomes your default belief,
and so thus a paper that says, well, it's more
difficult to rule out that kind of thing than you
might think. Uh, some people can erroneously conclude that that

(47:55):
is in fact evidence for the thing they want to
believe because it feels cool. It's not positive evidence for it, yes, yeah, absolutely,
um yes, So so you know, they argue that that
we need to to further research you know, the likely
signature uh left by our own um Anthropocene era, as
well as a deeper exploration of the elemental and um

(48:18):
compositional anomalies that we find in extant sediments. Basically, we
look at past events mainly with stuff like impacts in mind,
but perhaps the Silarian hypothesis needs to be at least
on the table as well. Not because again we think
it is, you know, actually a valid explanation for what
has happened. Um, you know, ultimately it's an outside possibility,

(48:41):
not a conclusion we should jump to, but perhaps it
should just be part of sort of the spectrum of
possibilities there again, not because we think it happened, but because, uh,
it gives us a little more of a sort of
a robust spectrum. And how to interpret these things and
and then moving forward to you know, potentially considering other worlds,
looking at other planets like even Mars. Uh. It gives

(49:03):
us one more tool, one more UH way to look
at the evidence. Yeah, exactly. They're not arguing this because
they think there was a civilization. It's that we should
consider these possibilities when looking at planets, even including our own,
and know what we would look for if we wanted
to consider that possibility, right, Because ultimately this is not

(49:23):
a supernatural explanation. This is ultimately, you know, a natural hypothesis.
But but it is admittedly an outside possibility. Now, of
course we're here talking about reasons why you shouldn't just
jump to the conclusion of a Salurian civilization. But but
there are also some arguments against it in some of

(49:43):
the specific events that they look at. For example, if
you know, maybe the best possibility is this interesting event
in Earth history, the Paleocene Eocene thermal maximum. More suddenly
there was there was rapid global warming and UH and
these in these chemical changes like with carbon isotopes. They
even put some arguments back against considering UH civilization as

(50:07):
a cause of this global warming in Earth's history. Because
they say, look, the kind of global warming caused by
our civilization is happening in an incredibly rapid fashion over
just a few hundred years. This actually, though it's it's
relatively rapid in geologic terms. The the p et M
actually happened probably over hundreds of thousands of years, which

(50:31):
which is incredibly slow if you're imagining that civilization was
the cause of it, right, if you're if you're comparing
it to the model of of human industrial advancement, it's
incredibly slow. So there's not only the point that you
shouldn't just jump to the conclusion of there was a
law civilization because it feels cool, but like in the
specific instances they look at, there are some reasons for

(50:53):
thinking that's probably not true. I don't know, I guess
unless those civilizations were like just really lazy. I mean,
you can sort of, you know, pull out your sci
fi hat and and put it on and come up
with various ideas of, you know, for why they might
have been this way. Maybe they were super long lived. Yeah,
they weren't very ambitious, and they're like this, note, this
is the right level of industrialization, and we want to, uh,

(51:15):
we need to keep going at this rate. I don't know,
they didn't reproduce all that much. I don't know. I
mean that that's ultimately one of the problems with with imagining, uh,
you know, other life forms. It's like it's just you know,
it's you can you can make a case for any
number of things, um and and try and make it

(51:37):
fit your your hypothesis. And of course that's not really
the way to go about it, I mean, not in
from a scientific perspective, from a sci fi dreaming creative perspective, yeah,
go for it. Um So, though I guess it does
kind of come down to the conundrum two at the
end of the day, like like when does when does
mere creativity and um and dream weaving become this kind

(51:59):
of corrupt of our thought and uh and and a
pollution of our ability to understand our place in the
world and are where we're going in the future and
where we were in the past. Well, you know, I
feel like a thread without maybe intending intending to do so,
that we've pursued a good bit on this podcast is
understanding the ideally the difference between your sort of interest

(52:21):
and imagination and your epistemology. That like that an idea.
You can like an idea because it's interesting and cool,
and that doesn't necessarily mean it's true. You know that,
like that, your your epistemology is probably best to based
on evidence, and you should be skeptical of things that
you want to believe because you like them and so forth.

(52:43):
But it's still totally valid to like, say, be interested
in the bicameral mind or whatever because it's a fun idea,
even if you know, you probably accepted as you know,
there's not a lot of evidence for it, right right,
You can you can alpoly engage in a number of
these ideas as as more as art than science, and
there there's nothing wrong with that. Is when you start
arguing that your art is science, that's where you can

(53:04):
get into into some trouble. Um. I was reminded in
all of this of Carl Sagan's approach to ancient aliens
and ancient astronauts, particularly in the book that he co
authored with Joseph Shklovsky Intelligent Life in the Universe. Um.
The in in this particular book, you know, the the
examine this idea. They said, okay, here's the speculative idea,

(53:26):
and we don't have evidence that had ever happened, But
if it were to have happened, what sorts of specific
evidence might we look for? And in this case, we're
talking about signs that are evident in ancient religions and
uh and so forth. Uh. And I thought that was
a great treatment of that question. Uh and against Sagan's
treatment reminds me of the treatment given in this paper

(53:48):
by these authors. But of course Segand had to come
back and continue to argue with the ancient alien people
who were you know, very much going off in their
own directions, yeah, and pushing pushing art as science, and
Sagan having to remind them like, no, I love art
as much as the next guy. But here's how we
approach this from a scientific perspective. Well, I mean, I

(54:09):
think the important thing about this stuff, like Sagan's work
on that or or or the paper we're looking at here,
is it's good too when you're when you're exploring it
like a tantalizing and juicy idea. It's a good idea
to have criteria for what would be good evidence of
such a thing before you're actually looking at individual evidence
in cases, because if you look at the evidence first

(54:31):
and then you try to come up with criteria. You're
gonna have a tendency to want to fit your criteria
to whatever evidence you've already got. The cherry picking model
or what is it the other name of the barn
wall fallacy or something like that. Remember, the idea is like,
you know, somebody says, you know, I'm a great shot,
and so they shoot at the side of a barn
and then they go up, they walk up to their

(54:52):
bullet hole, and then they draw a bull's eye perfectly
around it. That's that's a great point. That's that's a
great way of looking at it. All Right, Well, I
guess we're good and go ahead and wrap this episode up.
But we'd love to hear from everyone out there. I
love to hear from any doctor who fans who have
some additional information they want to share about the Silurians
and various related um species that have popped up in

(55:15):
that show. And perhaps you have specific thoughts about about
you know, just this this basic you know view uh
and what it reveals about humanities uh place on Earth
right now, and what technological civilization is doing to the planet,
and just you know, ultimately what kind of a you know,

(55:35):
a small blip a week signal we may be in
the future, as opposed to this kind of lasting thing
that we sometimes imagine that human civilization is. I'm going
to say, I hope that I'll be optimistic, so I
hope we do stick around. I hope we attenuate the
kinds of geologic signal we leave due to climate change
and chemical alteration of the atmosphere and all you know,

(55:58):
stuff like that, uh, and heavy metal pollutions and things,
and that we the signal of our civilization can always
be charted against the geologic record because of the continuance
of Doctor Who Seasons. So when we're on the like,
you know, eventually we'll get into the exponential notation of
the Doctor Who Seasons. Yeah, yeah, yeah. Well, one day

(56:18):
some sort of ancient U, or rather some sort of
far flung future civilization will look back and say, look,
clearly they knew what they were doing. Uh, they were
able to do you know, some three million years of
Doctor Who. Though maybe at a certain point the doctor
will be a robot and the enemies will be will
be organics, and I don't know, Yeah, I wonder at

(56:40):
what point do we get a robot doctor? I mean,
they they're they've only recently really been been been mixing
up the casting on that role. Al right, well, let
us know in the meantime if you want to listen
to other episodes of Stuff to Blow Your Mind, we
have core episodes on Tuesdays and Thursdays and the Stuff
to Blow your Mind podcast feed. On Monday's we do
listener Mail, where we hear from from you, the listeners,

(57:02):
and we read your various listener mails, always a good time.
On Wednesday's we do a short form artifact or monster fact,
and then on Friday's we do Weird How Cinema. That's
our time to set aside most serious issues and just
talk about a weird film. Huge thanks as always to
our excellent audio producer Seth Nicholas Johnson. If you would
like to get in touch with us with feedback on

(57:23):
this episode or any other, to suggest a topic for
the future, or just to say hello, you can email
us at contact at stuff to Blow your Mind dot com.
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(57:44):
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