Legends about a lost Golden Age are generally regarded as myths.
But could an advanced ancient civilization have existed on Earth without us knowing?
The Silurian Hypothesis attempts to address just this question.
This is Unveiled, and today we’re answering the extraordinary question:
are there advanced ancient civilizations still hidden on Earth?
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Archaeologists have sometimes struggled to provide explanations for the incredible technological
accomplishments of ancient civilizations. One classic example is the construction of the
Egyptian pyramids. For years, scholars have debated how people two and a half thousand
years ago were able to haul massive stone blocks to the sites and stack them in place.
There’s now a general consensus that the quarried blocks were transported on wooden sleds,
with water poured on the sand in front of them to reduce friction. The blocks were raised into place
using ramps and levering devices. Nonetheless, the gaps in our knowledge have led to other,
pseudoscientific theories, such as the idea that ancient aliens intervened to build various
structures. It’s a simple, catch-all explanation for diverse feats - like
attributing rainbows, floods, and other natural phenomena to divine intervention.
It’s also an idea that some academics have accused of having racist underpinnings - namely,
the assumption that only modern Europeans are capable of technological innovation.
There are also legends, however, about ancient human civilizations even more technologically
advanced than our own. The ‘lost’ city of Atlantis is a prime example. The legend began with Plato,
who mentioned Atlantis in an allegory about power, corruption, and the ideal state.
His account includes references to incredible wealth and a mysterious metal known as
orichalcum. Most scholars agree that the story is fictional, although there is some debate over
whether the legend could have been based on historical sources. In popular culture today,
Atlantis is often imagined as having had technologies far superior to our own.
The larger theme behind such stories is that our Golden Age lies behind us; we are now in decline.
The ancient Greek poet Hesiod expressed this notion in his poem “Works and Days”,
separating the ages of humankind into Golden, Silver, Bronze, Heroic, and Iron. The Golden Age
was a time of prosperity and peace; people didn’t age and the earth provided for all our needs.
It certainly sounds like a fantasy. But if such a glorious civilization
had existed in our past … would we know about it?
Scientists have wondered the same thing. In fact, this question, or thought experiment, has a name:
the Silurian hypothesis. It was first posed in a 2018 paper published in The International Journal
of Astrobiology by Adam Frank, an astrophysicist at the University of Rochester, and Gavin Schmidt,
director of NASA’s Goddard Institute for Space Studies. Their thought experiment takes its
name from a fictional species of reptilian humanoids in the TV series “Doctor Who”.
To avoid a global catastrophe, the Silurians withdrew into underground hibernation units.
Over millions of years, erosion and the movement of tectonic plates erased traces
of their existence. They emerged gradually back into a world that had long since forgotten them.
In their paper, Frank and Schmidt explored whether or not modern science would be able
to detect the existence of a lost industrial civilization in the geological record.
The answer has major consequences for astrobiology and the search for extraterrestrial life.
People who believe that an advanced civilization came before us have sought support in the
existence of out-of-place artifacts: objects that challenge conventional historical chronologies.
One famous example is the so-called Baghdad Battery, which according to a fringe theory
was used in electroplating. Another is the Antikythera mechanism, an Ancient Greek model of
the solar system that scientists have proclaimed the oldest known analogue computer. However, while
the Antikythera mechanism is impressive, it isn’t indicative of industrial levels of technology,
or some secret civilization. If an ancient industrial civilization had existed in human
history, that know-how likely would have spread, and we’d see signs in the archaeological record.
But what about non-human civilizations?
It might seem far-fetched, but consider how little we know about Earth’s history.
Our planet is about 4.5 billion years old. The first microscopic organisms emerged at
least 3.7 billion years ago, and complex life evolved around 1.6 billion years ago.
Apes have been around for just 25 million years, the genus Homo for two million, and modern humans
for only 300,000 years. Our civilization has been an industrial one for three centuries.
That’s just the blink of an eye in geological timescales. Is it impossible that some other
species achieved technological prowess millions of years ago? What would be the telltale signs?
As Adam Frank put it in an article for “The Atlantic”,
you could forget about looking for statues and ruins: “once you roll the clock back to
tens of millions or hundreds of millions of years, things get more complicated.”
Even fossils might not be much help. The process of fossilization is relatively rare,
which is why fossil records represent only a small fraction of life on Earth.
Just consider the meager fossil record that dinosaurs have left behind. Dinosaurs were
around for about 165 million years - but we only have a few thousand near-complete fossils!
And ‘dinosaurs’ consist of over 700 different known species. As Frank and Schmidt remark,
“species as short-lived as Homo sapiens (so far) might not be represented in the existing
fossil record at all.” So if, to borrow their example, some unknown mammal established an
advanced civilization during the Paleocene epoch 60 million years ago, it’s possible we wouldn’t
even have stumbled across its remains - even if it endured for thousands and thousands of years!
What about the objects that such a species had produced, though?
Well, while human activities have caused widespread destruction, we’ve currently
urbanized less than 1% of the Earth’s surface. And thanks to natural geological processes,
like the movement of tectonic plates, the Earth’s surface is always changing.
In fact, the oldest discovered surface on Earth, in Israel’s Negev Desert, is only
approximately 1.8 million years old. The rest of the exposed surface has long since been replaced.
If there were prehistoric roads or cities on it, they’ve been reduced to dust deep beneath the
surface. Even the ruins of societies that vanished just a few million years ago would be gone by now.
The secret to discovering them would probably lie instead in our planet’s sediments. The use
of fertilizers in industrial agriculture adds a significant amount of nitrogen to our soil. A
spike in the amount of rare-Earth elements used in electronics could be another indicator.
So too could the presence of synthetics such as steroids, and of course plastics. Millions
of tonnes of plastic end up in our oceans every year, breaking down into microplastics that now
fill every nook and cranny of the planet, including the digestive systems of living
organisms. These microplastics create layers that could be detectable millions of years from now.
Another giveaway would be the legacy left by fossil fuels. When we burn fossil fuels,
it releases carbon into the atmosphere, increasing CO2 levels and changing global temperatures.
Long after we’re gone, this will be evident in exposed rock layers and ice cores.
Interestingly, the planet has experienced these phenomena before.
During the Paleocene–Eocene Thermal Maximum period 56 million years ago, carbon and
oxygen isotope ratios spiked and the planet’s average temperatures soared. The difference,
however, is that these spikes occurred over the course of hundreds of thousands of years.
Due to industrialization, we’ve seen drastic rates of change within just a few hundred years.
On this basis, the Paleocene-Eocene Thermal Maximum probably has natural causes.
To notice the subtle signs of ancient industrialization, we’d have to study
the geological record carefully - especially if the civilization in question was short-lived.
This actually has important implications for astrobiology. As we comb the surface
of Mars for traces of past life, we need to keep our eyes open for these key markers.
Of course, a civilization doesn’t have to be industrial to be complex and advanced.
After all, our own species has spent the majority of its existence in pre-industrial times.
Like Ozymandias in Shelley’s poem, there may have been some prehistoric, pre-industrial species
that beheld its monuments and thought: “Look on my works, ye Mighty, and despair!” Maybe,
like us, they thought they’d be around forever. But if they did, we’ll probably never know.
There’s no evidence that an advanced, industrial civilization developed on
Earth before our own. However, it is possible that one existed!
Despite our knowledge of ancient species, from Trilobites to dinosaurs, it would be easy for
signs of an ancient, non-human civilization to have flown under the radar. We would have to look
attentively in the geological record. While we don’t know of any industrial
civilizations that predate the emergence of early humans, we can’t completely rule it out.
And that’s our best answer
to whether there are advanced ancient civilizations still hidden on Earth.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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