43: Civilization Before Humans? Silurian Hypothesis
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Hey, it's your buddy AJ from the Y-Files. And Hecklefish. Right, and Hecklefish. We just wanted to tell you that if you want to start a podcast, Spotify makes it easy. It'd have to be easy for humans to understand it. Will you stop that? I'm just saying. Spotify for Podcasters lets you record and edit podcasts from your computer. I don't have a computer. Do you have a phone? Of course I have a phone. I'm not a savage. Well, with Spotify, you can record podcasts from your phone, too.

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There are over 7 billion people living on the Earth right now. Tens of millions are born and die each year. Every single one of us leaves signs of our existence in the air, water, soil, even space. But these signs won't last forever. Our buildings will be gone in a few hundred years. Our stone monuments, plastic, styrofoam, Twinkies, even evidence of our inevitable nuclear destruction will eventually be gone. So how can we be sure that we were the first advanced civilization on Earth?

Well, according to the Silurian hypothesis, we can't. Let's find out why. Let's talk about the Silurian hypothesis. What the hell is a Silurian? Well, they were intelligent humanoid reptilians who, in an episode of Doctor Who, were awakened by nuclear testing after 400 million years of hibernation. Blizzard people? Yep. We're finally

We are. Well, kind of. Humans are selfish. It's hard for us to imagine that in a very short time, we as individuals won't be here.

And it's even harder to imagine a time where our civilization won't exist at all. But if we learned anything from archeology, it's that every civilization has its time. Think about ancient Egypt. They lived 30 dynasties that spanned over 3,000 years. And if you were an Egyptian living during this time, generations of your family going back as far as anyone can remember, walked in the shadow of the pyramids

They fished the Nile, they sailed the Mediterranean, mingled with other cultures. As far as you or anyone knew, your civilization had been there and would last forever.

Then it was gone. The Mesopotamians before them, the Indus after them, Greeks, Nubians, the Persians, Romans, Incas, Aztecs. These were empires of millions of people, all lasting a thousand years or more. But very little evidence of them remains. Now, all of these civilizations, including our own modern one, have only been here for a short time. Complex life has existed for hundreds of millions of years.

Modern humans have only been here for about 100,000 years. Our entire history has taken place in the past 0.002% of life on Earth. So there's a whole lot of past in the past. And that's plenty of time for other intelligent species to evolve, thrive, and go extinct.

over and over again with different species. And if that happened, would we really know they were here? When Adam Frank and Gavin Schmidt wrote the Silurian Hypothesis, they addressed a lot of misconceptions about how we study the past. We're used to the idea that we learn of ancient societies by examining artifacts and excavated ruins.

But this really only works if you're going back a few thousand years. But when you want to go back millions of years, it's more complicated. For example, the Earth is about 4.5 billion years old and complex life appeared about 600 million years ago. But the oldest surface land ever discovered is the Negev Desert in Israel. It's about 1.8 million years old. That's it. Every other piece of exposed land we've ever found is newer than that. So where'd all the land go?

If ancient civilizations existed before humans, they could be very hard to detect. Because of the Earth's plate tectonics, today's mountains are yesterday's ocean floor. New land is formed every day as old lands are eroded into dust. That's why discovering fossils is a lot more difficult than people think.

Very specific conditions need to be present for fossilization. The organism needs hard body parts like bones, teeth, and shells. The remains need to be quickly covered and protected from scavenging and erosion. You need high pressure for mineralization and low oxygen to prevent decomposition.

This almost never happens. Dinosaurs roam the Earth for about 180 million years. Trillions of individual animals lived and died, yet we only have a few thousand near-complete fossils. It's estimated that over 2.5 billion Tyrannosaurus rexes lived and died on the Earth, but fewer than 100 fossils have ever been found, and only one of them is complete. That means we've only discovered 0.000000.

Schmidt and Frank said that a species as short-lived as Homo sapiens might not be represented in the existing fossil record at all.

Now, the current area of urbanization is less than 1% of the Earth's surface. So human artifacts like roads, cities, machines, even megastructures would last only a few thousand years and are unlikely to ever be found. They conclude that direct evidence like this can only go back about 4 million years. Even if the entire human race were eliminated by a nuclear war, the radioactive evidence would disappear eventually. So what?

Are there other methods for detecting the existence of advanced intelligent life in the distant past? Turns out, there are. Civilization, at least as defined by the authors of the Solarian Hypothesis, is where industrialization occurs on a global scale, as ours does. Now, as we speak, industrialization is leaving clues of our existence that will be detectable by scientists 100 million years in the future.

Now eventually, our time on Earth will be crushed down to nothing more than a thin layer of rock sediment. Yeah, that's uplifting. Now in a sedimentary core, a layer of a few centimeters is deposited every thousand years. And in those centimeters, future paleontologists will find evidence of our geologic era called the Anthropocene. Now for example, we grow so much food now that our use of fertilizer is actually redirecting the planet's nitrogen supply. Why?

And this nitrogen cycling is also changing its isotopic signature. And this isotope will be detectable in the sediment. Agriculture and deforestation increase soil erosion, and that erosion washes into the sea and becomes part of the sediment. Human mining activities have increased the amounts of gold, lead, chromium, platinum, and other metals. And these also will be visible in the sediment at greater rates than before. But the element that will really tell the story of civilization?

Humans conquered the planet by harnessing combustion. And it seems reasonable that intelligent life forms everywhere would do the same thing. When we burn the tissue of long-dead plants, fossil fuels, we change the ratio of isotopes in the atmosphere. And this is called the Seuss effect. The green omelet guy? Different Seuss. Yeah.

Yeah. Carbon comes in 15 flavors, but the most common isotopes are carbon-12, carbon-13, and carbon-14. Carbon-12 is light carbon. This is the isotope preferred by plants and used during photosynthesis. And animals that eat plants consume the plant's carbon-12. And animals that eat animals that eat plants consume their carbon-12, and so on. Now, volcanic emissions are carbon-13. Carbon-14 is radioactive and decays predictably over time. Fossil fuels have no carbon-14 at all.

And as we burn more fossil fuels, the levels of carbon-13 and 14 go down, while the level of enriched carbon-12 goes up. All this carbon in the atmosphere also causes the Earth to warm slightly. Blech. What? Global warming is a myth. It's not. Sheep. Look, you can argue that the warming is man-made or that it's not, but either way, we're up about a degree. Blech!

Anyway, when looking through sedimentary layers from millions of years ago, this is what we need to see to determine if there was advanced civilization present. We need to see a large but temporary spike in carbon and oxygen, a large but temporary spike in metals, and a large but temporary spike in global temperature. We find that, we're onto something. Have we found that? Have we? We have, and it happened 56 million years ago. The age of the lizard people!

A sudden global change of carbon and oxygen isotope levels happened 56 million years ago in what's known as the Paleocene-Eocene Thermal Maximum, or PETM. And the PETM only lasted about 200,000 years. Now that's nothing in geologic time.

But remember, that's as long as we've been here. And during this time, the P.E.T.M., the Earth's temperature rose about 6 degrees Celsius. Now that was warm. I mean, we're talking T-shirt weather at the North Pole warm. I mean, the ice caps were completely gone. Lizard people do like warm weather. What? Lizard people are cold-blooded. Hello? Read a science book? There were no lizard people. Bleh! So is the P.E.T.M. evidence of an ancient civilization? Yep.

Probably not. It took 5,000 years to reach the level of carbon in the atmosphere that we've done in only 300 years. So what caused it? Nobody knows. The best guess is the PETM was caused by a massive volcanic eruption, but nobody knows for sure. What's weird, though, is there is evidence of a lot of fossil carbon in the atmosphere. Lizard people gas stations.

And a few million years later, these conditions happened again. And this event is called the Eocene Layers of Mysterious Origins. Sounds like the name of a Harry Potter book. It does. And there were other massive events in the Cretaceous period that depleted the Earth's oceans of oxygen for thousands of years. Now, to be honest, most scientists believe that we are the first civilization. But they do admit that if an advanced species only existed for as long as we have...

they would be really hard to detect. Even the authors of the Silurian Hypothesis admit if you're not specifically looking at the right time in history and for the right details, you'll probably miss it. But the Silurian Hypothesis does give us an interesting set of tools. Tools that might not help us find ancient civilizations on our planet, but could help us find them on other planets.

The Drake equation is a well-known formula for estimating the number of extraterrestrial civilizations in our galaxy. It boils down to the number of stars that have planets, the number of planets that can support life, the fraction of those planets that develop life, and the fraction of those that can develop intelligent life. Now, this number fluctuates as new discoveries are made,

But still, the number of civilizations out there could be anywhere from 150,000 to 1.5 billion. Even if it's just more than one, it would be so cool. So cool. What's interesting is, now that we had the Silurian hypothesis, any planet that can develop intelligent life

can maybe develop it again and again over millions or billions of years. And that was the original premise of Frank and Schmidt's paper. They wondered not only about life on other planets in the galaxy, but about civilizations that may have existed right here in our solar system.

At one time, Mars was much wetter and much warmer. So was Venus. One of Jupiter's moons, Europa, is covered by a saltwater ocean. When we finally get core samples from these planets, we may realize that, though civilizations don't exist there right now, the distant past could tell a very different story. Now, the authors of the Silurian hypothesis don't believe there were ancient civilizations on Earth before humans. And our civilization may be unique in the universe,

But they do lay out an exciting possibility that there could be millions of civilizations out there. And now we have the tools to find them. Thank you so much for hanging out with us today. My name is AJ. That's Hecklefish. This has been the Y-Files. If you had fun or learned anything, do me a favor and like, subscribe, comment, and share. Trying to solve the YouTube algorithm is like trying to discover ancient civilizations.

But with your help, we can do it. Until next time, be safe, be kind, and know that you are appreciated.