Could a Pre-Human Advanced Civilization Exist on Earth?

According to astrobiologist Adam Frank, advanced civilizations in the universe might trigger climate shifts just as humans are doing today, raising questions about whether all those that harness energy on a global scale are destined to burn out or survive for millions of years. Frank and NASA scientist Gavin Schmidt investigated this premise through the Silurian hypothesis, a thought experiment exploring whether an advanced civilization lived on Earth millions of years ago.

The Silurian Hypothesis Origins at NASA

University of Rochester professor Adam Frank walked into the office of NASA scientist Gavin Schmidt in 2017 with what he believed was the weirdest question: do aliens experience climate change? Frank told Schmidt he was looking at other planets because there had been no other civilizations on Earth. Schmidt immediately cut him off and asked how Frank knew that, according to interviews about the research.

That exchange started an investigation into whether an advanced civilization could have lived on Earth millions of years ago, powered themselves with energy, and wiped themselves out without leaving obvious traces. The researchers named the concept the Silurian hypothesis after a fictional advanced race of reptiles from the television show Doctor Who, publishing a paper on the idea in 2018.

Investigating Ancient Climate Anomalies Like the PETM

Schmidt began mulling the possibility of previous advanced civilizations due to ancient events in Earth’s history. Around 55 million years ago, global climate signals went haywire during the Paleocene-Eocene Thermal Maximum (PETM), a period first noted in the 1990s. Global temperatures spiked up to 15 degrees Fahrenheit, ecosystems collapsed, and huge amounts of carbon entered the atmosphere.

While scientists attribute the PETM to enormous volcanic eruptions or sudden methane releases, the exact cause remains a mystery. Schmidt noted similarities to modern temperature spikes and extinctions driven by humans. Other periods in deep geological history also experienced oxygen-starved oceans and sharp temperature hikes, prompting Frank and Schmidt to test what kind of evidence a past advanced civilization might leave behind.

What Physical and Chemical Traces Would Remain?

Surface features offer little direct evidence of ancient societies because tectonic activity and erosion constantly reshape the planet. The Earth’s oldest large-scale stretch of land is the Negev Desert in southern Israel, at around 1.8 million years old. Furthermore, animal fossilization is rare; dinosaurs roamed for about 180 million years, but researchers have discovered only a few thousand near-complete fossils.

Because a 100,000-year civilization would appear as a mere blip in the 400-million-year history of complex life, Frank and Schmidt examined chemical changes instead. Rock strata, such as those visible in the Grand Canyon, keep a memory of past Earth chemistry. If a previous civilization altered the planet’s chemistry with carbon pollution, future scientists could detect it. Artificial hormones for agriculture, persistent chemicals, plastics, and electronics-grade heavy metals would also persist in sediments millions of years later.

“The point of the paper wasn’t to establish whether the Silurian hypothesis is correct,” Frank said, noting the goal was to identify what scientists should look for in a much more high-resolution way to determine if a civilization existed before us. Neither Frank nor Schmidt believes the theory is definitively true; they argue it simply cannot be ruled out yet.

Scientific Critiques and the Longevity of Modern Technology

Geologist, paleontologist and emeritus professor at the University of Leicester in the UK Jan Zalasiewicz called the Silurian hypothesis a wonderful and deeply thought-provoking idea. However, Zalasiewicz argued that Schmidt and Frank underestimated how much modern humans have transformed the planet and the effectiveness of the fossilization process in preserving history.

Zalasiewicz is comfortable ruling out the prior existence of an energy-guzzling, manipulative, constructional society that produces waste in colossal quantities because cities, metal smelting, and discarded plastics leave an unmistakable footprint. “As soon cities are built, metals are smelted, plastics are made and discarded — these will leave a clear footprint,” Zalasiewicz said.

Atmospheric scientist Katharine Hayhoe at Texas Tech University, who was not involved in the research, noted that the thought experiment exposes global vulnerabilities. “These questions are all relevant to exactly the moment that we’re in,” Frank said, pointing out that humanity is pushing the planet into a new climate regime without taking adequate action.

Frequently Asked Questions

What is the Silurian hypothesis?

The Silurian hypothesis is a scientific thought experiment proposing that an advanced civilization could have lived on Earth millions of years ago and left behind subtle physical or chemical traces in the geological record.

Who created the Silurian hypothesis?

Astrobiologist Adam Frank from the University of Rochester and NASA scientist Gavin Schmidt developed the concept and published a paper on it in 2018.

Why don’t we see more physical ruins from millions of years ago?

Tectonic plate shifts, volcanic eruptions, and land erosion continually resculpt the Earth’s surface, erasing surface structures over millions of years.

Can we rule out a prior industrial civilization on Earth?

Researchers like Jan Zalasiewicz argue that the scale of modern industrial activity, waste, and technofossils makes the prior existence of the kind of advanced civilization we live in today unlikely, though debate continues.