Could Earth Have Once Harbored a Pre-Human Industrial Civilization?

Fernando Kaskais

Sep 1

the lost city of atlantis, being rediscovered by its ancient builders

MARK STEVENSON/STOCKTREK IMAGESGETTY IMAGES

Forget Ancient Aliens. Say hello to the "Silurian hypothesis."

The Silurian hypothesis asks whether it might be possible to find evidence of a pre-human industrial civilization in Earth's geologic record—even one that might have existed millions of years ago.
The astrobiologists who developed the thought experiment concluded that there is not strong evidence in Earth's geologic record to support such a claim.
However, we still lack the scientific methods that would allow us to dive deep into Earth's behaviors over such a long time span, so we may want to keep an open mind.

Complex life on our planet has existed for at least 400 million years. Yet as a species, we only managed to create an industrial civilization around 300 years ago. But, what if an earlier industrial civilization existed on Earth millions of years ago? If that were so, how would we be able to prove it—or disprove it? This is the crux of the Silurian hypothesis, a fascinating thought experiment that appeared in a study published in 2018 in the International Journal of Astrobiology.

The possibility of life elsewhere in the universe and its parallels with the Anthropocene—the current geological epoch, during which humans have impacted Earth to the point of no return—has long puzzled Adam Frank, a professor of astrophysics at the University of Rochester, New York, and one of the two authors of the study.

"Is it common for any civilization that reaches our level of energy use to trigger their own version of climate change? I was wondering. If there are alien civilizations, would they also trigger climate change?" Frank ponders. With this whirlwind of thoughts in mind, Frank visited the NASA Goddard Institute of Space Sciences (GISS), an elite climate-science facility at the University of Columbia, New York. He wanted to share his thoughts with climate researchers, and surely expected lots of raised eyebrows and skeptical stares in the process.

"I went into the meeting with Gavin A. Schmidt [a climatologist and the director of NASA GISS], and started talking about aliens. And then Gavin stopped me and said, 'Wait a second. How do you know we're the only time there's been a civilization on our own planet?'''Frank tells

Evidence in Earth's Geologic Record

UNITED STATES GEOLOGICAL SURVEY, PUBLIC DOMAIN, VIA WIKIMEDIA COMMONS

Geological time spiral illustration, silurian hypothesis prehuman industrial civilization.

Homo sapiens first appeared on Earth about 300,000 years ago. In the unlikely case that such an old industrial civilization had existed, it would predate the species to which we all belong. It was then that Schmidt called the idea the Silurian hypothesis, paying homage to the sophisticated reptilian humanoids awoken by nuclear testing after 400 million years of hibernation in a 1970s episode of the British science fiction television series Doctor Who. The study authors decided to laser in on the time period from four million years ago to 400 million years ago.

Going back hundreds of millions of years to find traces of a potential pre-Homo Sapiens civilization is not a piece of cake. "After a few million years, Earth is pretty much resurfaced. You're not going to have any statues, buildings, or anything left," Frank says. Fossil records will be virtually nonexistent as everything will have crumbled to dust. The only evidence would come in the form of chemical imprints. "You'd have to look at each layer of rock, and then try and detect trends—look for changes in things like the carbon or oxygen isotopes, which are tracers of things like carbon dioxide. An industrial civilization would dump lots of carbon dioxide into the atmosphere, just like we do," Frank says. Plastic or nanoparticles would also be good indicators of an industrial civilization that occurred in time immemorial.

Schmidt and Frank were intrigued by the period of geological history known as the Paleocene-Eocene Thermal Maximum (PETM), because something peculiar happened on our planet during it, 56 million years ago: Earth's average temperature soared to 15 degrees Fahrenheit above what we have today, and the world became a temperate and iceless place. They investigated the carbon and oxygen isotope ratios from the PETM and indeed saw spikes, but they also saw declines, and all of these over a few hundred thousand years, which is nowhere near the speed at which carbon is currently suffocating the atmosphere. Frank says the PETM's chemical differences pointed to a long-term climate change.

They also reviewed other "abrupt events" throughout time that are visible in the geologic record, including ocean anoxic events—when an ocean becomes depleted of oxygen—and extinction events. Unsurprisingly, and perhaps slightly disappointingly, they were not indicative of an industrial civilization, either...

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