The Idea of the Silurian Hypothesis
If intelligent life existed elsewhere in the Universe, how would we know?
This was the question which astrophysicist Adam Frank had made a career trying to answer.
In early-2017, Frank came up with a groundbreaking idea. Was it possible, he wondered, that any advanced industrial civilization which arose on any planet would trigger a planetary climate shift, much as humans have done on Earth? If so, Frank realized, finding evidence of quick temperature rises on other planets might be the first step in finding evidence of intelligent life.
Seeking to explore the possibility further, Frank took his idea to NASA and its prestigious Goddard Institute for Space Studies, where, in short order, he found himself in the office of the institute’s director, Gavin Schmidt.
He began to present his idea, but just as he was building momentum, Schmidt suddenly interrupted. “Wait a second,” Schmidt said, “how do you know we’re the only time there’s been a civilization on our own planet.”
The question stopped Frank in his tracks. “I felt a kind of temporal vertigo,” he recalled, as the implication of the question dawned on him.
Modern human beings have been around for about 300,000 years, with an advanced industrial civilization arising in only the past 300 years. Yet, complex life has existed on Earth for 400 million years. In other words, there has certainly been more than enough time for the rise and fall of one or more advanced civilizations in the Earth’s history before humanity. What Schmidt was saying was that if Frank was proposing a way to look for ancient evidence of intelligent life on distant planets, why not apply this idea to our own planet?
This sent Frank’s mind racing. Here was the director of a prestigious NASA institute suggesting that an advanced industrial civilization, intelligent life, so to speak, could have existed on Earth many millions of years before human beings ever showed up.
Was this possible? Could what humans have achieved have happened before on Earth? And if so, how would we know?
Evidence of an Ancient Civilization
It might seem like it would be easy to tell if an advanced civilization had existed on Earth in the past. Presumably, all we would have to do is look for the same type of physical evidence which has been discovered from more recent ancient civilizations – evidence of buildings and roads, fragments of art or written works. That is to say, we would uncover evidence of advanced civilization millions of years in the past much the same way as we did for, say, the ancient Egyptians or Aztecs.
But in fact, it’s not that simple.
The problem is that the Earth’s geological record does not go back past what is called the Quaternary Period, some 2.6 million years ago. Go back further than that, and “everything has been turned over and crushed to dust.” If an advanced civilization did exist millions of years in the past, we would not find evidence of their cities and roads, and culture, which have long since been returned to the Earth.
But what about fossils? It might seem that surely an advanced ancient civilization would leave evidence of their existence in the fossil record.
In reality, this is not necessarily true. Just think about dinosaurs, who existed on Earth for 165 million years. To this day, only a few thousand “full” dinosaur specimens have been found, as in less than 20 for every million years the dinosaurs existed.
Consider humanity’s current industrial civilization, which has arisen in only the last 300 years. Even if this industrial civilization lasts for another million years, it would still only be a fraction of the length of time dinosaurs existed. In other words, it is unlikely that, in the long run, our own advanced industrial civilization is going to show up in the fossil record at all. The same would likely be true for an advanced industrial civilization which existed millions of years in the past.
Frank and Schmidt knew that evidence of an advanced civilization on Earth millions of years in the past would not come through this type of direct evidence – they would not be hunting for ancient ruins or fossils.
So what type of evidence, they asked, would exist?
As Frank later described, the two men realized that “The best way to answer this question is to figure out what evidence we’d leave behind if human civilization collapsed at its current stage of development.” Simply, “once [a] civilization reaches truly planetary scales, there has to be some feedback on the coupled planetary systems that gave it life,” indelible footprints left on the planet’s ecosystems, its air, water, rock, and its climate. It was these footprints which Frank and Schmidt believed would be the key to finding an advanced ancient civilization.
In 2018, the two men published a paper in the International Journal of Astrobiology which laid out in detail the various geological footprints they believed could serve as evidence of advanced industrial civilization in the Earth’s past.
The paper caused an uproar in the scientific world, raising not only the mind-blowing possibility of advanced civilization in Earth’s past, but asking difficult questions about the impacts of our own advanced civilization on the planet.
They called their theory “The Silurian Hypothesis.”
The Silurian Hypothesis
To start, Frank and Schmidt thought about the type of agriculture necessary to feed the planet’s nearly 8 billion people. To produce food on this scale, our industrial civilization has discovered ways to artificially “fix” nitrogen, breaking down the chemical bonds which hold nitrogen atoms together in the atmosphere to create biologically useful molecules which are used as fertilizers.
Our large-scale fertilizer use in agriculture is already changing the planet’s nitrogen flows in a way that is detectable in the Earth’s sediments. Similar evidence of changes in the Earth’s nitrogen flows in the past, Frank and Schmidt proposed, could be one piece of evidence indicating the existence of an advanced industrial civilization.
Next, they considered plastics, which over the past 75 years humans have been dumping into the ocean in enormous quantities. Over time, this plastic is ground down and eroded by the wind, sun, and waves, creating microscopic plastic particles which eventually sink to the ocean floor.
Already, after less than a century, studies show this plastic “marine litter” forming a layer on the sea floor in coastal areas, deep basins, and even the arctic. A similar layer now buried beneath the ocean floor might indicate an advanced civilization in the past.
Going further, Frank and Schmidt realized that plastics are not the only human-made elements we’re leaving behind. There are the rare earth elements used in modern electronics which have been extracted from hidden pockets within the Earth and spread all over globe. There are non-naturally occurring chemicals that we manufacture industrially, which are already appearing in the Earth’s sediments. There are even the radioactive isotopes related to nuclear activity. Plutonium-244, for example, has a half-life of 80.8 million years, meaning if an advanced ancient civilization conducted nuclear activity on a wide scale, it may show up in the record today.
It was not just what we are leaving behind which Frank and Schmidt considered, but how we are physically changing the Earth. Large scale agriculture and mass deforestation have led to increased soil erosion all over the world, while rising sea levels cause further erosion in coastal areas, and rising temperatures in the polar regions increase erosion by melting ice and thawing permafrost. These human-made changes in the Earth’s sedimentological records may show up deep it the future, or from deep in the past.
Yet, for Frank and Schmidt, all of these factors together paled in significance to another factor, the one which had started them on the road to their Silurian Hypothesis in the first place. Simply, if you’re going to have an advanced industrial civilization, you’ve got to power it.
Since the mid-18th century, humans have powered their civilization by burning fossil fuels, and the impacts this has had on the planet are significant. When fossil fuels get burned, the ratio of carbon-12 to carbon-13 usually found in the Earth’s atmosphere, oceans, and soils is altered. Already, humanity’s use of fossil fuels has changed this ratio significantly, in a way which will show up in the Earth’s geological record. According to Frank and Schmidt, a similarly dramatic change in the Earth’s carbon ratio deep in the past might suggest that somebody else was burning fossil fuels.
There is also the issue of temperature. Humanity’s industrialization has been accompanied by a warming of about 1.8°F since the 18th century, with more substantial rises projected in the future. In the long-term, a global temperature spike will be detectable in geological records contained within oceans, rock, plants, and ice.
Adam Frank had started with the idea that evidence of a climate shift on a distant planet might be evidence of intelligent life sometime deep in the past. In bringing this idea to Gavin Schmidt, the two men had come up with something even more incredible, that perhaps similar evidence might exist on our own planet.
Looking at the potential evidence they had compiled, Frank asked, “If these are traces our civilization is bound to leave for the future, might the same ‘signals’ exist right now in rocks just waiting to tell us of civilizations long gone?”
It is important to mention that both Frank and Schmidt outwardly believed the answer to this question was no.
Within their Silurian Hypothesis, they explicitly stated, “We strongly doubt that any previous industrial civilization existed before our own,” and when the paper was published, Frank bluntly told The Washington Post, “I don’t believe an industrial civilization existed on Earth before our own — I don’t think there was a dinosaur civilization or a giant tree sloth civilization.”
In fact, Frank and Schmidt devoted much of the space within the paper to poking holes in their own theory.
They admitted that much of the potential evidence they were talking about may not be unique to human activity, even if it was discovered. Dramatic spikes and changes in the Earth’s geological record can result from things like meteor strikes and volcanic eruptions, or any number of other factors.
Moreover, they recognized that the specific markers they were talking about as potential evidence – things like fertilizers, plastics, chemicals, and fossil fuels – represented a very specific path to advancement taken by human beings. If another advanced civilization had arisen in the past, there would be no guarantee it would have developed in the same way.
Additionally, if there was an advanced industrial civilization in the past, it might be expected that the longer it lasted, the larger the geological footprint it would leave, the more potential evidence out there for us to find. But, according to Frank and Schmidt, even this is not necessarily true.
Think about the point humanity is currently at, and what we are learning about our own existence. Clearly, we now recognize we cannot continue to burn fossil fuels and pollute the planet the way we have been and hope to survive. The point is that the longer a civilization lasts, the more sustainable its practices must become to survive, meaning that the footprint of an advanced industrial civilization might be self-limiting – either the civilization won’t survive long enough to leave a detectable footprint, or they will develop sustainable practices which will lower their footprint beyond detectability.
Perhaps Frank and Schmidt were right to be skeptical of their own potential evidence. Perhaps we wouldn’t be able to find said evidence; perhaps it never existed at all.
And yet, Frank and Schmidt did not intend their Silurian Hypothesis to be an end, but rather, a beginning. In their paper, they assert that merely “Asking the question in a formal way that articulates explicitly what evidence for such a civilization might look like raises its own useful questions related both to astrobiology and to Anthropocene studies.”
More simply, as Frank told The Washington Post, “The whole point of science is to ask a question and see where it leads.”
Evidence Supporting the Silurian Hypothesis
After publication of the Silurian Hypothesis, many took this advice to heart, following the theory to see where it might lead. Almost immediately, it was pointed out that exactly the type of potential evidence Frank and Schmidt were talking about already exists in our current scientific record.
It’s called the Paleocene-Eocene Thermal Maximum, a time period 55 million years ago when the Earth’s temperature mysteriously jumped between 9-15° F, at the same time as the planet’s carbon ratios shifted dramatically. Could this be evidence of an ancient advanced industrial civilization burning fossil fuels?
One thing is for sure, Frank and Schmidt were well aware of this event. While constructing their theory, it stood as such a poignant example of what they were talking about, that it ended up providing the basis for the title of the project.
While they outwardly professed to doubt the viability of their Silurian Hypothesis, Frank and Schmidt perhaps left a hint of their true beliefs in this title …
In a 1970 episode of the popular television series Doctor Who, the doctor is called to investigate the caves underneath a nuclear facility which is experiencing malfunctions. There, deep underground, he discovers a species of reptilian humanoids. He learns from these reptilians that they were part of an advanced civilization on Earth during the Eocene era, some 55 million years ago.
Their name? The Silurians.
This was where Frank and Schmidt got the name for their theory – a fictional advanced race that lived on Earth 55 million years ago, at exactly the moment when the Paleocene-Eocene Thermal Maximum was providing perhaps the best evidence currently on record for an advanced industrial civilization in the past. Some might call this an easter egg, but either way, it was no accident they called their theory the Silurian Hypothesis.
Since it was so important to Frank and Schmidt, the story of Doctor Who’s Silurians can be explored further, and the idea followed to see where it leads.
According to the story, at the height of their power, the Silurians discovered that a massive planetoid was set to blaze closely past the Earth, drawing away the Earth’s atmosphere in a way which would be catastrophic for anyone living on the planet. To survive this impending catastrophe, the Silurians retreated underground and put themselves into stasis, intending to remain in this self-induced hibernation until the Earth’s atmosphere returned, at which point they would be automatically awoken from their slumber. However, the planetoid did not end up passing the Earth, but rather, being captured by its orbit, becoming the moon. This caused the mechanism which was supposed to wake the Silurians back up to malfunction, leaving them in stasis for millions of years.
Think of this story as it relates to modern humans. Today, as the effects of climate change are felt all over the world, humanity’s elite are making plans to survive the impending catastrophe. This is why people like Elon Musk are so interested in rockets and colonizing Mars – when the Earth becomes uninhabitable for humans, they’ll just leave.
If it’s happening now, then why wouldn’t an advanced civilization in the distant past also have made plans to ensure their survival in the face of catastrophe, whether by leaving the planet, or by putting themselves into stasis, as the Silurians did.
The question can be asked in another way: if there was an advanced ancient civilization, what happened to them? What if they survived?
Dale Russel's Dinosauroid
Born December 27, 1937, Dale Russell rose from humble beginnings on a farm near Enterprise, Oregon, to become no less than one of the 20th century’s greatest paleontologists.
His first great foray into the field would come in the 1950s during his time as a student at the University of Oregon, when, on summer breaks, Russell would work in the fossil-rich dinosaur beds of southeastern Oregon. From there, he moved quickly, earning a master’s degree in paleontology from UC Berkeley in 1960 and a Ph.D. from Columbia in 1964.
By 1965, not yet 30 years old, Russell had accepted a position as the Curator of Fossil Vertebrates at the Canadian Museum of Nature in the nation’s capital of Ottawa. There, he would become a true legend of paleontology, describing numerous new specimens and becoming one of the first to consider the now widely accepted theory that an asteroid caused the extinction of the dinosaurs. He even helped lead the Canada-China Dinosaur Project from 1986-1991, acting as not just a scientist, but a diplomat.
Yet, for all his success, what Dale Russell is best known for today is a journey which began in 1969. That year, Russell analyzed a newly discovered skeleton of a Stenonychosaurus. While fossils from this dinosaur had first been discovered back in the 1920s, this was the first time a more complete skeleton would be described. In doing so, Russell noticed something stunning.
The brain cavity of the Stenonychosaurus was much, much larger than would be expected in a dinosaur. In fact, Russell estimated the volume of the brain to be seven times the volume of the brain of a modern alligator of equivalent mass, suggesting an intelligence beyond what was previously imagined in dinosaurs.
This started Russell thinking. What if dinosaurs hadn’t gone extinct 65 million years ago? Here was a dinosaur with an abnormally large brain; what if it had continued to evolve?
Russell worked with the thought for years, until finally, in 1982, he introduced the world to his famed dinosauroid thought experiment. In it, Russell imagined an evolutionary path for the Stenonychosaurus, its development into a humanoid being with a large head for a large brain, an upright stance and forward-facing eyes, and three-fingered hands for the manipulation of tools. Russell called it the dinosauroid, and even commissioned a life-size model of the creature.
Immediately, Russell’s work caused an uproar, inspiring heated dialogue in both science and popular culture. Many questioned, was this type of evolution really possible? Could it really have taken place if dinosaurs hadn’t suddenly gone extinct? Would humans even have existed if they had?
There was something else, however, another implication of the dinosauroid which many missed initially.
Dinosaurs have been extinct for 65 million years. Yet, before that, they existed on Earth for 165 million years. If it was possible, as Russell was suggesting, for dinosaurs to evolve into advanced humanoid beings in the 65 million years since their extinction, then surely it is also possible for this to have taken place in the 165 million years before that.
Look at it another way. In the last 300,000 years, humans have gone from living in trees to using iPhones. Dinosaurs were around for 500 times longer than that.
Maybe the question is not so much what would have happened had dinosaurs not gone extinct, but what might have happened in the time before they did. Remember the Silurian Hypothesis. If dinosaurs did evolve into advanced beings like Russell’s dinosauroid, or Doctor Who’s Silurians, maybe we just haven’t found a record of it yet.
There is an additional question to ask here. If a cataclysm did come to Earth millions of years ago, such as the one which science tells us wiped out the dinosaurs, would an advanced civilization not have attempted to ensure their survival, whether by going into stasis like the Silurians, or fleeing the planet like Elon Musk?
Here, one might wonder, if they did go into stasis, did they wake up? If they left, will they come back?
Ancient Reptilian Race
Currently, the accepted record of human civilization on Earth goes back somewhere between about 6,000 and 10,000 years. Throughout this time, one consistent theme has emerged, a connecting thought across human cultures around the world. Again and again, in myth and record, stories appear of reptilian creatures interacting with humans.
From the carvings of ancient Egypt and Sumer to the gods of Greek and Asian mythology, to Hindu traditions and the traditions of the ancient Aztecs, to even the serpent in the biblical story of Adam and Eve, each culture tells its own stories of reptilians.
Is it possible that these stories are more than myth?
Perhaps they are records of the descendants of an advanced race which existed on Earth millions of years before humans, awakened from stasis, or returned from outer space. Maybe these are Russell’s dinosauroids, Frank and Schmidt’s Silurians.
To this day, some believe that a reptilian species exists on Earth, perhaps even controlling humanity, as the purported gods of the ancients did, through positions of power and prestige.
Whether or not this is true, taking a step back we can see that the Silurian Hypothesis has achieved its objective – Frank and Schmidt have asked the question, allowing us to see where it leads.
And where it leads are thoughts of an advanced race evolving in a distant past, questions of what happened to such a race, if they did exist. Moreover, it leads to an opportunity to think about our own existence, our own mortality as a human race, the idea that someone just like us could have existed in the past, rising as we have before eventually falling.
All this time we’ve been looking out into space for signs that we are not alone in the Universe. Maybe we should have been looking at our own planet all along.