Deep Dive
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For Adam Frank, the weirder a question is, the better. Adam's an astrophysicist who's interested in looking for life in deep space.
And a few years back, he had a thought. I was interested in, amazingly enough, I was interested in whether or not aliens trigger climate change on their own planets. I mean, literally. Maybe rapid climate change on a faraway planet could be a sign of an advanced civilization. You know, maybe any civilization that, you know, has to mature through the phase that we're going through will do this.
Adam wanted a second opinion, so he started running his idea by some climate scientists. And of course, you know, this is a pretty crazy idea. It's like, hey, I want to talk to you about aliens and climate change. So I always have to sort of do this backpedaling because I expect people to raise their eyebrows. Which is exactly the reaction he kept getting.
until he got to Gavin Schmidt. Yeah, so, I mean, I have nothing against being slightly odd. And that's, you know, that's perhaps part of my persona. Gavin's a climate scientist at NASA. And so I go in and I, you know, that's the first thing I drop on Gavin's lap is, you know, I want to talk about
about climate change and aliens, because I said, you know, of course there's never been another civilization on Earth, you know? And that's as far as I got when he said, "Well, how do you know there's never been another civilization on Earth?" - And he says, "What?" And I said, "Well, yeah, how do you know that we are the first technological species on Earth?" - And I was like,
You know, it's just like instant break and my draw was on the floor. And that kind of floored him for a little bit because I don't think he'd ever thought about it. Yeah, I was just sort of stunned because, of course, like I never had thought about that. Of course, there's never been another civilization on Earth before. To be clear, Gavin was suggesting that there might have been an advanced technological species on Earth before humans.
This was a radical idea for anyone, but especially for Adam and other astrophysicists who were looking for extraterrestrial life. They were looking in space, but I'm saying, well, no, look in time as well. It was like one of those things like those telescoping moments in a dream when you're like...
Because suddenly I had this feeling of deep time, like suddenly dropping back into the Earth's, you know, 10 million, 30 million, 100 million year history, just like, you know, expanding in front of me. You know, it was a vertigo. It was kind of temporal vertigo that I had. Even for Adam, this was just a whole new level of strange. I came in thinking like, wow, there's
Nobody is going to talk about anything weirder than I have with climate change and aliens. And in five seconds, he out-weirded me. Initially, it was a joke. It was like, oh, you know, this is just a fun thought. And he said, well, actually, that's a very deep thought. How would we know? What would be left? I'm Noam Hassenfeld, and this week on Unexplainable, the search for terrestrial intelligence.
Last week, we talked about the search for intelligent life in deep space. So this week, we wanted to share a favorite episode of ours that flips that search towards our own planet. Are humans really the first technologically advanced species on Earth? And if there were an intelligent, industrialized civilization millions of years before us, how would we know?
You're looking at a kind of world that hasn't existed for millions of years. Hasn't existed. Millions and millions and millions. It's almost as if time forgot this place. Is there life on Mars? There's a whole universe out there, Steve, beyond anyone's comprehension.
Let's just start with some context on the scale of things. When you hear ancient civilizations, you're probably thinking of humans, maybe the Egyptians or the Mayans or the Babylonians. But when you zoom out, those societies were doing their thing pretty recently, just a few thousand years ago. Gavin and Adam were focusing on a time millions of years before humans even evolved. And all that time before humans is just enormous.
To paraphrase Douglas Adams, the universe is very, very big. So deep time is very, very big. Space is big enough that it's easy to assume there must be alien life out there. But deep time is pretty enormous too. Animal life has been on land for 400 million years. And modern humans have only been around for a tiny fraction of that. Not even half a million. So is there space out there?
for other kinds of species to kind of evolve, develop, become industrial, take over the world, and then disappear. Yeah, there's a lot of space. But it's pretty hard to imagine what an ancient technological species from Earth might have been like. Science fiction is full of stories of intelligent aliens from other worlds. But when Gavin and Adam tried to find sci-fi about aliens from Earth...
they didn't find much. The earliest example they came across at the time was from some 1970 Doctor Who episodes about a species called the Silurians. And the Silurians were a, they were nominally some lizard type. Reptilian, biped. That was woken up because of some, you know, strange nuclear tests. They're an alien life form, as intelligent as we are. And they were an indigenous species. They weren't aliens. They were an indigenous species. We were here before man.
We ruled this world millions of years ago. That had got in trouble, put themselves to sleep, and then were waking up and they're saying, well, what are you vermin doing on our planet? This planet is ours. It always has been. So with Doctor Who in mind, Gavin and Adam wrote up a paper they called the Silurian Hypothesis. It was basically a thought experiment. How would we know if a species like the Silurians, intelligent, technological, industrialized,
how would we know if they existed millions of years before humans? To find an answer, they needed to know what kind of evidence to look for. So instead of turning to the past, they imagined going into the far future and looking back on the remnants of our civilization. If our society collapses, whether it's because of an asteroid or a pandemic or apocalyptic climate change, and some future scientists are looking for signs of us millions of years from now,
Are they going to know we were here? We started off by kind of framing it with, what would we see if we were looking back at our current period through the lens of geological history? Where are you going to see our traces? The idea that there would only be traces of us, it might seem a little surprising at first. But even humanity's most impressive monuments won't make it.
The Eiffel Tower, the Great Wall, the pyramids. I mean, the pyramids are, you know, four or five thousand years old. Things like that have stuck around for thousands of years, but not hundreds of thousands of years, and not through an ice age cycle, and not millions of years. It can be a little destabilizing if you really think about it. Humanity as a whole can sometimes feel like it'll just keep going on forever.
But on the scale of millions and millions of years, forever just takes on a different meaning. There'll be ice ages, floods, fires. Erosion, rain, wind, glaciers, sea. Until the entire surface of the Earth is completely churned up and erased. It turns out that the oldest existing surface that's still the surface is basically the Negev Desert, which is about, you know, 1.7 million years old.
If the entire history of animal life on land were equal to the length of a day, the surface of the Negev would only be about six minutes old. And that's the oldest surface on Earth. Everywhere else has been erased by glaciers, chewed up by forests, dissolved by rain, eroded by wind, has fallen into the ocean because of earthquakes. Everything else has been reworked or buried.
Just think about that last scene from Planet of the Apes. The Statue of Liberty is already half underwater, and that's only something like 2,000 years into the future. He finally really did it. You maniac! When Gavin is wondering what would be left of us in millions of years, he's imagining a point thousands of times further than the Planet of the Apes future. It's honestly hard to wrap your mind around. Damn you all day!
So buildings won't be around to prove we were here in millions of years. But what about fossils? Things can get fossilized, but very little does. It's actually pretty hard to end up as a fossil. You'd have to be very unlucky. You'd have to pretty much fall into a tar pit or...
or get caught in an ash flow from a big volcano, but not burn, right? So it can't be so warm that you fry. You have to kind of fall in a swamp exactly at the right time so that you get preserved, but you don't rot. And when you think about it in context,
we haven't really found that many fossils. The number of individual dinosaurs whose fossils we've found is basically one individual every 10,000 years for more than 100 million years. So we found a lot of dinosaurs. But in terms of the percentage of dinosaurs that ever lived that we found, it's a tiny, tiny fraction. Fossils of us also probably wouldn't show that we were technologically advanced.
And given how unlikely it is for anything to fossilize in the first place, it's a pretty unreliable way to guarantee that the future would know about us.
But all this lack of evidence isn't exactly surprising. It's very unlikely you're going to find somebody kind of popping up and saying, Hi, I'm a technological civilization. Instead, Gavin says if we were to look back on us from the far future, we might be able to find things we didn't mean to leave behind. What we're detecting when we're looking at our impact is our waste. It's not our art. It's not our literature. It's our detritus. So the question is...
Where are we going to see this waste? And the answer is you're going to see it in the ocean sediments. You're going to see it in the kind of things that get compacted into sedimentary rocks. And you're going to see this layer of the Anthropocene. The Anthropocene is sometimes defined as the period in which humanity has impacted the geologic record, which you can see in various layers of sediment.
As the surface of the Earth gets burnt and flooded and eroded over millions and millions of years, different layers of rock start to form. Each layer corresponds to a different period of time, and scientists can read these layers like a book. So if we traveled millions of years into the future and we were trying to read the layer of the Anthropocene, Gavin's co-writer Adam Frank says we would be able to recognize it by looking at particular atoms in the sediment called isotopes.
Isotopes are versions of elements that have more or less neutrons. Elements are defined by how many protons they have. So, for example, carbon always has six protons. But there are a bunch of different carbon isotopes. You know, there's carbon-12.
And there's carbon-13. The 13 part is like there's an extra neutron in it. And we can learn a lot about the past just from looking at ancient isotopes. Isotopes become either clocks, thermometers. There's all different kinds of ways in which you can use those isotopes to read the history of the planet. Burning fossil fuels gives off a particular kind of carbon isotope. And all these isotopes gradually settle into the sediment over time.
So if we were looking back on the Anthropocene from 50 million years in the future, we'd be able to see our fossil fuel use in the geologic record.
And we know that the signature of carbon isotopes sticks around for hundreds of millions of years. But Gavin says that's not the only sign we'll see. We're going to see this massive change in nitrogen isotopes. We'll see this because of the massive amounts of artificial fertilizer we put into the ground. We're going to see global warming, the temperature changes. We're going to see all these spikes in heavy metals. Because we're mining them, throwing them into the ocean as waste. We might even see a layer of plastic.
Plastics may be maintained for many, many hundreds of millions of years. All in all, if we disappear tomorrow and some future scientist is searching for evidence of us, the proof of our advanced technology, from the invention of farming to the invention of the iPhone, it'll be tiny. And unless a layer of plastic ends up surviving that long, this future scientist would then have to wonder, is the change they're noticing in the isotopes really evidence of a civilization?
Or could it just be some sort of natural blip? All you see when you do the measurements is that the temperature changed, or that the nitrogen isotopes changed, or that the carbon isotopes changed, or that there was this spike in metals. And there's all sorts of natural reasons why that could have happened, right? So the question is, how would you know? This question, how would you know, it was something Gavin would have to answer as he turned his attention to the deep past.
Because he had a pretty intriguing 56 million year old clue. But was it actually the sign of an ancient technologically advanced civilization? That's next. This episode is brought to you by Shopify. Whether you're selling a little or a lot.
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Hey, unexplainable listeners. Sue Bird here. And I'm Megan Rapinoe. Women's sports are reaching new heights these days, and there's so much to talk about and so much to explain. You mean, like, why do female athletes make less money on average than male athletes?
Great question. So, Sue and I are launching a podcast where we're going to deep dive into all things sports, and then some. We're calling it A Touch More. Because women's sports is everything. Pop culture, economics, politics, you name it. And there's no better folks than us to talk about what happens on the court or on the field.
and everywhere else, too. And we're going to share a little bit about our lives together as well. Not just the cool stuff like MetGalas and All-Star Games, but our day-to-day lives as well. You say that like our day-to-day lives aren't glamorous. True. Whether it's breaking down the biggest games or discussing the latest headlines, we'll be bringing a touch more insight into the world of sports and beyond. Follow A Touch More wherever you get your podcasts. New episodes drop every Wednesday. ♪♪
Unexplainable. We're back. When we left off, climate scientist Gavin Schmidt was imagining what might be left of us in the far future, millions of years after humanity has disappeared. But if future scientists do see evidence of climate change in the geologic record, how are they going to know it's because of us? How would they know it's not a natural blip?
Turns out, years before Adam ever came to his office, Gavin and other climate scientists were looking at ancient records of climate change, seeing how the ratio of carbon isotopes changed over time. And they noticed a blip just like this 56 million years ago. You know, when it kind of moves up and down and this kind of long-term changes, and then suddenly there's this like massive decrease, and it falls off the graph, and then it comes back again almost immediately.
That blip showed that there was some serious climate change 56 million years ago. There could have been all sorts of causes, but the levels looked weirdly similar to the climate change we're causing today. So Gavin started to wonder about what was behind this ancient blip. Well, wouldn't it be funny if the cause was the same too? What if this blip was evidence of some ancient technological civilization that caused their own climate change 56 million years ago? Whee!
So Gavin posed the idea to Adam. It's just like a freaky deaky question, right? And sometimes there's nothing better than like thinking about a freaky deaky question. And they started looking for other blips in the geologic record that looked suspiciously like the Anthropocene, starting with Gavin's 56 million year old blip. And you can go back further. There's something around 120 million years ago.
There was something that's similar in the Jurassic. It's getting a little bit harder to see what's going on. But you can go back to the Permian-Triassic extinction event, and that's going back 250 million years.
And do we know if these are just blips? Like, is there anything else in these layers that might be a sign that you're looking at some kind of ancient, advanced technological species? Well, as far as we know, we haven't discovered any unnatural chemicals in any of these deposits. We haven't discovered any plastics layers in any of these deposits. We haven't discovered any nuclear fallout in these deposits. And so we haven't detected any of those things.
But we could imagine a civilization that didn't make a lot of plastic or nuke itself, right? Well, yes, why not? You know, you see the things that we've done and you say, well, that's just because of the way we organize our society. Exactly. Because of the way we develop technology. But that, you know, why would you imagine that that was some kind of universal truth? It's obviously not, right? So then you go back and you kind of think, well, what are the essentials? Yeah, if it's not...
plastic or nuclear weapons or something, what would be
common to all advanced civilizations. Well, we went back and forth on this quite a lot, but the essentials are basically energy and an energy perhaps derived from fossil fuels, and then that gives you this carbon isotope marker. That's the blip you saw in the geologic record 56 million years ago. Right. So then you say, okay, well, that's perhaps necessary, but that's not sufficient. Right. We're not going to be convinced that that means that there was another civilization. We're going to need more. Right.
And I assume we don't have more? Well, but there's lots of things they haven't found because they haven't looked.
So the number of people looking for exotic isotopes of plutonium in deep sea sediments is quite small. The number of people looking for man-made chemicals in a hundred million year old sediment is also quite small. But people have to look before we can dismiss it completely. And if you're only looking for like waste, is it possible that there was some advanced civilization back there that we can't see because it just,
just used renewable energy or something? Right. So if civilizations become sustainable, then you may not be able to detect them at all. So we have this kind of paradox that, you know, it's possible that we will never be able to find the long-lived civilizations because they're
they're long-lived and sustainable. And we can only find the things that burn themselves to a crisp. And the civilizations that burn themselves to a crisp would probably also be harder to find, right? Because they would have to last a significant length, right? And they only last a very short... Right, right. It's like the universe is conspiring against us to try and find other civilizations, right? Like the shorter ones, hard to find. The longer ones, hard to find. Right. But...
It seems unlikely. I mean, I'll just ask you, like, do you think there was an advanced civilization before humans? There is no evidence. So, you know, should people find evidence? I think that would be very interesting. But, you know, the paper that we wrote and the discussion that started since then is really a question of how do you know
There might not be conclusive evidence of a Silurian-like civilization, but that doesn't mean the question isn't still worth asking. Scientists do this kind of thing all the time. Just think about the search for civilizations on other planets. For a long time, you know, NASA wouldn't fund anything to do with a search for biosignatures of alien life. You know, that was also seen as somewhat suspect.
But that has gone as we've discovered thousands of exoplanets around many, many, many different kinds of stars. And so the science has broadened.
The Silurian hypothesis could also eventually lead to all sorts of unexpected discoveries. But at least for now, Gavin's 56-million-year-old blip is just a blip. Not a clear sign of an ancient civilization. Probably just some natural changes in the past. I mean, you know, when I talk about this, I'm not trying to convince people that there were, you know, ancient civilizations. But just to think about...
What would have been left? That thought can provide a powerful shift in perspective. A lot of people don't realize how much of a geological force we are.
But then you point out that, you know, what we're doing is as large as anything that's happened over the last 65 million years. Then it's like, oh, oh, oh, well, maybe that's a big deal then. You know, maybe, maybe, maybe one degree temperature, maybe 1.5, maybe two degrees. Maybe that's a big deal. That kind of reaction is exactly what Gavin is going for. The sort of telescoping moment. Yeah.
that Adam had when he first heard the question. You know, everything in science is about the right question. Because the right question that has not been asked before can pry open all kinds of things. Like, yeah, I do not think that there was a previous civilization, but the question of how would you know if there was suddenly opens the doors to how do civilizations and planets evolve together? In this sense, the Silurian hypothesis raises a bigger question.
What kind of society do we want to be? Do we want to be easier to find or harder to find in millions of years? We can burn very brightly for a short amount of time, but we can't sustain that. And so we have to transition if we want to be a long-lived species. So the question is whether that's possible. When we take this extremely zoomed-out perspective, history is almost impossibly long. We may not even be the first civilization that's asked whether we were the first civilization.
And when we think about when the universe is likely going to end, we're not even halfway there. There's more than enough room for our civilization to disappear and for tons of future ones to come around, not knowing we were ever even here. That's the thought that I take away most from the Silurian hypothesis. We are not forever. And if we don't make a concerted effort to stick around, everything we've ever done, everything we know,
It all might end up as some future scientist's freaky deaky question. This episode was reported and produced by me, Noam Hassenfeld. Edits from Catherine Wells, with help from Brian Resnick and Meredith Hodnot. Mixing and sound design from Christian Ayala and Afim Shapiro. Music from me, fact-checking from Richard Sima, and Manding Nguyen staring at the sun. Bird Pinkerton blinked as her eyes adjusted to the darkness. Two platypuses stood over her, arguing.
Do you have the antidote? No. Don't. You? Oh, yeah. Okay. If you have thoughts about the show, send us an email. We're at unexplainable at vox.com, and we'd love to hear your thoughts, your suggestions, any ideas you have. And if you can, go leave us a review or a rating wherever you listen. It really helps us find new listeners.
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