Advanced NASA Theorists Contemplate: Could We Be Latecomers to Earth's High-Tech History?
In the grand saga of Earth's four-billion-year history, a mere 300 years isn't much to write home about. Yet, this brief blink—our industrial era—has upended the atmosphere, oceans, and sediments. If civilization vanished tomorrow, would even a piece of us endure 100 million years from now? Could extraterrestrial beings stumbling upon Earth years from now ever recognize this world as a haven for an advanced species? What if another civilization inhabited our planet long before us - could we even spot the signs?
Enter the Silurian Hypothesis—a thought-provoking yet serious proposition, born from the minds of Gavin Schmidt, a NASA climate scientist, and Adam Frank, an astrophysicist. They detailed this idea in a 2018 paper for the International Journal of Astrobiology. The name of this hypothesis is a nod to the Silurians, an ancient, intelligent reptile species from Doctor Who, but the premise is grounded in geology, astrobiology, and climate science.
To set the record straight, the authors assert, "We are not suggesting that intelligent reptiles actually existed in the Silurian age. Nor that experimental nuclear physics is liable to jolt them out of hibernation."
Lost to the Ages?
At the heart of the Silurian Hypothesis is a profound inquiry: if an industrial civilization sprung up millions of years ago—say, during the Devonian or the Paleocene—would we find any tangible remains of it today?
According to Schmidt and Frank, the chances are slim.
The geological record is patchy at best. Oceanic crust, where a significant portion of sediments settle, gets recycled every 170 million years or so. On land, surface preservation is even more elusive. "The current area of urbanization accounts for less than 1% of Earth's surface," they point out, and antique surfaces that remain intact are a scarce find.
Additionally, even comparatively recent human fossils are hard to come by. The odds of spotting fossilized remnants or a lost city from a civilization that existed 10 or 100 million years ago are virtually negligible.
Signs in the Soil?
However, a civilization's presence could be discerned through its planetary footprint.
If industry was in play, energy was burned, land use changed, and the atmosphere was altered. These changes could leave subtle marks in the rock record, which scientists call "geochemical fingerprints." Our own footprint, though brief, has already left such a mark. Carbon dioxide concentrations have skyrocketed, oceans have warmed and acidified, and plastic particles rain into marine sediments. Persistent synthetic chemicals, like PCBs, and even radioactive isotopes from nuclear tests linger for millions of years.
"The longer human civilization endures, the more pronounced the signal one would expect in the record," they write. But there's a paradox: "The more sustainable a society... the smaller the footprint."
A civilization powered by renewable energy might leave hardly a trace, while a short-lived one fueled by fossil carbon would leave a distinctive signature, much like modern human activity does today.
As they mined Earth's geological past, Schmidt and Frank identified events that eerily mirror today's Anthropocene era. The Paleocene-Eocene Thermal Maximum (PETM), a sudden global warming event 56 million years ago, is a striking example. During the PETM, temperatures jumped 5-7°C, ocean acidity soared, and mass extinctions swept through the deep sea. Some metal levels peaked, and erosion increased—features that echo human-induced changes today.
Other instances include Ocean Anoxic Events in the Cretaceous and Jurassic periods, which left behind black shale deposits and peculiar chemical signatures. In some cases, these events also coincided with large carbon isotope anomalies, just like today. Nevertheless, these ancient phenomena are generally linked to volcanic activity or tectonic upheaval. To argue that they result from a vanished civilization would require robust evidence.
Frank and Schmidt themselves aren't entirely convinced that an industrial civilization existed prior to ours.
"Raising the possibility of a prior industrial civilization may lead to unbridled speculation," the authors warn. "Care must be taken not to postulate such a cause until solid evidence is available."
Implications Today—and Tomorrow
This intellectual exercise could bear real significance. It underscores our limited understanding of the longevity of civilizations—ours included. If industrial civilizations tend to implode quickly, their geological legacy might be meager. We might never even stumble upon their trace, just like countless human societies—along with their language, customs, stories, and inventions—have vanished across history.
Moreover, this hypothesis alters how we approach the search for extraterrestrial intelligent life. The renowned Drake Equation, which predicts the number of communicating civilizations in our galaxy, includes a term for how long these civilizations endure. If advanced societies self-destruct or shift to sustainable models that produce little geological impact, then the probability of detecting them plummets.
Schmidt and Frank urge scientists to broaden their thinking: "Could there be other compounds that will leave distinct traces in the sediment geochemistry on a multi-million-year scale?" they ask. Might deep drilling on Mars, Venus, or other celestial bodies reveal similar fingerprints?
The Silurian Hypothesis doesn't aim to prove that an ancient civilization existed before our own. As we've seen, it would be almost impossible to deduce this from the faintest geological signs. Instead, it's more about asking what traces civilizations leave behind—and what that tells us about our own.
"While we strongly doubt that any earlier industrial civilization existed before ours, asking the question in a formal way... raises its own useful questions related both to astrobiology and Anthropocene studies," the authors conclude.
- If an industrial civilization emerged millions of years ago, such as during the Devonian or the Paleocene, it's unlikely that we would find any tangible remains of it today due to the geological record being patchy, particularly with oceanic crust being recycled every 170 million years and limited surface preservation on land.
- However, a civilization's presence could be discerned through its planetary footprint, as changes in energy usage, land use, and atmospheric composition could leave geochemical fingerprints in the rock record.
- The authors of the Silurian Hypothesis, Gavin Schmidt and Adam Frank, suggest that the longer a civilization endures, the more pronounced its geological footprint will be, but ironically, a more sustainable society might leave hardly any trace.
- The Silurian Hypothesis could have real implications regarding our understanding of civilization longevity and the search for extraterrestrial intelligent life, as it might alter how we approach the Drake Equation and the assessment of geological signs on other celestial bodies.
- Schmidt and Frank challenge scientists to consider if there are other compounds that could leave distinct traces in sediment geochemistry on a multi-million-year scale, and if deep drilling on Mars, Venus, or other celestial bodies could reveal similar fingerprints.
- The Silurian Hypothesis primarily aims to raise questions related to astrobiology and Anthropocene studies, encouraging us to ponder the traces civilizations leave behind and what that tells us about our own civilization on Earth.
