If another advanced civilization lived on Earth before us, would we know?
When astrobiologist Adam Frank walked into NASA scientist Gavin Schmidt’s office, he was confronted with what he believed to be the strangest question: Are aliens experiencing climate change? It only took Schmidt a few minutes to take him down.
Looking for signs of life in the universe, University of Rochester professor Frank was investigating whether advanced civilizations would inevitably trigger climate changes. people are doing this now. He was looking at other planets, he told Schmidt that day in 2017, “because of course we know there are no other civilizations on Earth.”
Schmidt immediately interrupted him. “How do you know this?” he asked.
Frank said this was a record-breaking moment and launched two scientists on an investigation. If an advanced civilization lived on Earth millions of years ago and produced energy using energy and destroyed themselves, can we know? Would they leave traces of their presence etched into the records of our planet?
Inspired by the fictional advanced reptile race from the TV show “Doctor Who,” they called this idea the “Silurian hypothesis” and published a paper. paper On top of that in 2018.
It’s a mind-blowing idea that looks not only deep into Earth’s past, but also into its future; because humans are changing the climate rapidly and dramatically by burning fossil fuels. “It’s a thought experiment, but it’s an experiment that reveals our potential vulnerability globally,” said atmospheric scientist Katharine Hayhoe of Texas Tech University, who was not involved in the research.
The Silurean hypothesis raises big questions about the course of advanced civilizations and whether all those that use energy on a global scale are doomed to extinction or have a chance of living sustainably and surviving for millions of years.
“These questions are all relevant to the exact moment we are in,” Frank said. “We’re forcing the planet into a new climate regime…we know that’s true, right? And yet we’re doing nothing about it.”
The Silurian is a fictional character from the TV show “Doctor Who” who is part of an advanced reptilian race that predates humans. – Everett Collection
Schmidt’s reason Thinking about the possibility of previous advanced civilizations existing on Earth was a thing of the past.
About 55 million years ago, the planet’s climate signals went out of control. As vast amounts of planet-warming carbon were injected into the atmosphere, global temperatures rose by as much as 15 degrees Fahrenheit and ecosystems collapsed.
This period, known as the Paleocene-Eocene Thermal Maximum and first recorded in the 1990s, may be the result of a massive volcanic eruption or perhaps a sudden release of methane. But exactly why this happens is still a mystery. What intrigued Schmidt were the similarities to what’s happening in humans now. increase temperatures And trigger extinctions.
And this isn’t the only unexplained change in the planet’s past that reflects the present; It was also seen in other periods. oceans starved of oxygen and sharp increases in temperature.
Most likely these are natural climatic events, but what if they are not? How can we know? In their report, Frank and Schmidt examine the possible chain of evidence supporting an advanced civilization in the past.
Only 1% of the Earth’s surface is urbanized today, and it won’t be long before what we’ve built is wiped out. The further back in time a hypothetical civilization existed, the harder it would be to find direct evidence, such as objects.
Over millions of years, the planet is reshaped as tectonic plates shift, volcanoes erupt and soils erode. The world’s oldest large-scale land mass is the Negev Desert in southern Israel, which is approximately 1.8 million years old.
Sand dunes in the bright sun in Israel’s Negev Desert. This is the oldest large-scale terrain in the world. – Smith Collection/Gado/Getty Images
Surface features may not provide much evidence, so scientists examined fossils. However, a vanishingly small fraction of animal species have been fossilized, and even fewer have been found. Dinosaurs roamed the Earth for approximately 180 million years, but only a few thousand complete fossils have been discovered.
It can be easy to overlook a civilization that has existed for only 100,000 years, just one blip in the 400-million-year history of complex life on the planet.
researchers Then the traces left by chemical changes were taken into account. “Think of the Grand Canyon,” Frank said; here you can see rows representing different ages of the Earth. “Each of these layers is composed of ground-up rocks that preserve a memory of what the Earth’s chemistry was like back then.” If an earlier civilization had altered the chemistry of the planet, as humans did by releasing large amounts of carbon pollution – may be a recording.
The scientists also considered what other evidence people might have left behind later. Our civilization is over, as are artificial hormones for agriculture as well as large amounts of plastic. permanent chemicalsdoes not break down in the environment. All of these may appear in future sediments millions of years from now. Like heavy metals used in electronics.
Frank said the purpose of the paper was not to determine whether the Silurian hypothesis was correct. Instead, “his point was to say that the things you would want to look for to see if there was a civilization before ours are here in a much higher resolution.”
Both Frank and Schmidt are in the awkward position of having written a study about a theory that neither of them believes in; they just say we can’t rule it out yet.
Since then, no one seems to have accepted the call for deeper research, but some scientists have raised questions.
Jan Zalasiewicz, a geologist, paleontologist and emeritus professor at the University of Leicester in the United Kingdom, said the Silurian hypothesis was a “wonderful and deeply thought-provoking idea.” But Schmidt and Frank said they underestimated how much modern humans have transformed the planet, as well as “the effectiveness of the fossilization process and how good it is to preserve the history of what happened on our planet.”
We can’t rule out intelligent prehuman societies, such as “dinosaurs that could sing complex arias or Jurassic ammonites that could compose poetry,” said Zalasiewicz, co-author of the 2025 book “Discarded: Technofossils Will Be Our Final Heritage.” But when cities are built, metals are melted, plastics are produced and discarded, they will leave a clear footprint, he said.
Zalasiewicz conveniently ignores the previous existence of the type of advanced civilization we live in today: “energy-consuming, manipulative, constructive, and producing enormous amounts of waste.”
That’s the beauty of science, Frank said. “You publish an article, you say, ‘Wow, that’s great,’ and then someone comes along and says you’re wrong.” Someone else might find something that points in a different direction, and eventually, as research accumulates, a consensus will emerge.
Perhaps the most important reason to examine this hypothesis for now is the important questions it raises about the longevity of advanced technological civilizations like ours.
We’re smart enough to develop technology, but we may not be smart enough to understand how to deal with its climate-changing consequences, Frank said. “Are we an experiment the planet is running that will fail?”
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