Could an advanced technological civilization have thrived on Earth millions of years before humans, leaving behind only subtle chemical and physical traces?
The Silurian Hypothesis: Searching the Geological Record for Prehistoric Civilizations
When astrobiologist Adam Frank walked into the office of NASA scientist Gavin Schmidt back in 2017, he brought what he considered a bizarre question about whether alien civilizations experience climate change. Schmidt immediately flipped the premise.
That exchange prompted the two researchers to formulate the Silurian hypothesis
—named after a fictional race of reptiles from the television show Doctor Who
—to investigate whether an industrial society could have existed millions of years ago and subsequently vanished. The core difficulty in finding such a civilization lies in planetary erosion. The oldest large-scale stretch of land on Earth is the Negev Desert in southern Israel, which dates back roughly 1.8 million years. Tectonic shifts, volcanic eruptions, and weathering continually resculpt the surface, erasing cities and artifacts.
To bypass the absence of surface relics, researchers look to the planet’s chemical memory. In places like the Grand Canyon, rock strata record ancient atmospheric chemistry. A prehistoric civilization burning fossil fuels on a global scale would leave behind distinct geochemical signatures, heavy metals from electronics, and persistent synthetic compounds trapped in future sediments.
Parallels in Deep Time: The Paleocene-Eocene Thermal Maximum
The motivation behind investigating ancient civilizations stems partly from unexplained climate spikes in Earth’s history. Around 55 million years ago, global temperatures rose by up to 15 degrees Fahrenheit during an event known as the Paleocene-Eocene Thermal Maximum. Ecosystems collapsed as vast quantities of carbon entered the atmosphere. While scientists generally attribute this event to massive volcanic activity or methane releases, the parallels to modern anthropogenic warming raise compelling questions about planetary history.
Other ancient periods show oceans starved of oxygen and sudden temperature spikes. While these events are likely natural, distinguishing a natural climate catastrophe from an industrial collapse remains a central challenge for researchers investigating deep time.
Interstellar Visitors and Cosmic Seeding
Beyond Earth’s internal history, researchers are also looking outward at interstellar objects entering our solar system. According to nypost.com, meter-scale rocks from interstellar space may impact Earth roughly once per decade, potentially totaling half a billion collisions over the planet’s existence.
Since most stars formed a billion years before our sun, an advanced civilization from an earlier star system could have had ample time to explore or seed life across the galaxy. Astronomers have confirmed three interstellar objects in our solar system: 1I/ʻOumuamua in 2017, 2I/Borisov in 2019, and 3I/ATLAS in 2025. While NASA classifies 3I/ATLAS as a comet, Loeb has speculated about potential artificial characteristics, noting unusual non-cometary traits.
We may have a family of technological civilizations like ours or intelligence civilizations that we are not aware of,
Loeb told the outlet, describing them as technological siblings that managed to leave their home planets early.
Refocusing Priorities on Space Exploration
Both lines of inquiry—the Silurian hypothesis and the study of interstellar interlopers—serve as warnings for modern human society. Frank noted that humanity is currently pushing Earth into a new climate regime while failing to enact sustainable changes. Similarly, Loeb argues that intelligent civilizations often perish due to geopolitical conflicts on their home planets unless they expand outward into the cosmos.
To avoid a similar fate, Loeb advocates reallocating portions of military budgets toward deep-space expeditions. As researchers continue to monitor incoming interstellar objects and analyze geological strata for ancient anomalies, the search for past technological civilizations offers a stark lens through which to view humanity’s current environmental and technological trajectory.
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