The Silurian hypothesis is a thought experiment that tests modern science’s ability to detect evidence of an advanced society that existed millions of years ago.
Adam Frank, an astrophysicist at the University of Rochester, and Gavin Schmidt, director of the NASA Goddard Institute, wondered if it would be feasible to detect an advanced civilization before humans in a 2018 publication.
“While we have strong doubts that any previous industrial civilization existed before ours,” they wrote, “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 Anthropocene studies.”
The phrase “Silurian hypothesis” was inspired by the Silurians from the 1970s Doctor Who series Doctor Who and the Silurians.
According to Frank and Schmidt, the chances of finding direct evidence of such a society, such as technical items, are slim because fossilization is uncommon and little of Earth’s visible surface dates before the quaternary time period.
Schmidt told Newsweek that “we are already a geophysical force,” and that “our presence is being recorded in carbon, oxygen, and nitrogen isotopes, extinctions, additional sedimentation, spikes in heavy metals, and synthetic compounds (including plastics).”
Despite the fact that industrialization only began roughly 300 years ago, the human burning of fossil fuels is already having an impact on the geological record. Furthermore, global warming, agribusiness, and the proliferation of manmade contaminants all have an impact.
So, if some other species on Earth rose to civilization for a brief period of time millions of years ago, would there be any indications of them now, such as fossils or the remnants of buildings?
“Perhaps,” Schmidt responded, “but it’s also possible that all such evidence has been ground to dust and the only traces left are in the more subtle geochemical perturbations.”
Furthermore, because “fossilization is highly unusual and partial,” “evidence could easily have been missed,” particularly if a civilization lasted only a few thousand or tens of thousands of years, as ours did.
The researchers determined that after such a long period of time, indirect evidence such as anomalies in the chemical composition or isotope ratios of sediments would be more likely to be discovered. Plastics and nuclear waste residues buried deep below or on the ocean floor could suggest possible remnants of past civilizations.
Previous civilizations may have ventured into space and left relics on other celestial bodies like the Moon and Mars. Artifacts would be easier to find on these two worlds than on Earth, where erosion and tectonic action would obliterate much of it.
Frank approached Schmidt initially to discuss how to discover alien civilizations by studying ice cores and tree rings to see how their possible impact on climate may be detected.
Because people have only been in their current form for 300,000 years and have only had advanced technology for a few centuries, they both realized that the concept could be enlarged and applied to Earth and humanity.