Silurian hypothesis

Lore & Background

Frank and Schmidt imagined the existence of an advanced civilization before humans and considered whether it would be possible to detect an industrial civilization in the geological record. They argued that as early as the Carboniferous period (~350 million years ago) there has been sufficient fossil carbon to fuel an industrial civilization comparable with our own. However, they also wrote that they strongly doubt any previous industrial civilization existed before our own, but asking the question formally raises useful questions related to astrobiology and Anthropocene studies.

According to Frank and Schmidt, since fossilization is relatively rare and little of Earth's exposed surface has survived from before the Quaternary time period (~2.5 million years ago), there would be low probability of finding direct evidence such as technological artifacts. Instead, researchers might find indirect evidence such as rapid changes in temperature or climate, evidence of tapping geothermal power sources, or anomalies of chemical composition in sediment such as evidence of artificial fertilizers or isotope ratios. The paper also mentioned the natural fission reactors at Oklo, Gabon, which were active some two billion years BP, noting that none of the transuranic elements produced are still present, but the depletion of 235U and characteristic isotope ratios of fission products confirm that fission had occurred.

Frank and Schmidt speculated that such a civilization could have gone to space and left artifacts on other celestial bodies, such as the Moon and Mars, where erosion and tectonic activity would be less likely to erase evidence. The idea has been connected to the cryptoterrestrial hypothesis explaining the existence of UFOs.

Reader's Guide

The Silurian hypothesis serves as a formal framework for considering what geological traces an industrial civilization might leave behind, even if no such civilization is believed to have existed. By articulating explicit evidence that might be found—such as climate changes, sediment anomalies, or traces of nuclear waste—the hypothesis raises useful questions for astrobiology and Anthropocene studies. It challenges researchers to think about how future scientists might detect our own civilization's impact, and it extends to the possibility of finding artifacts on the Moon or Mars, where preservation conditions are better. The hypothesis also highlights the rarity of fossilization and the limited survival of Earth's exposed surface, underscoring the difficulty of detecting any pre-human technological society. Jan Zalasiewicz, a geologist and emeritus professor at the University of Leicester, claims that Schmidt and Frank seriously underestimate how much evidence would be left by an advanced civilization, indicating ongoing debate within the scientific community.

Did You Know?

• The Silurian hypothesis was proposed by astrophysicist Adam Frank and climate scientist Gavin Schmidt in a 2018 paper.
• The name 'Silurian' was derived from a sapient species in the BBC science fiction series Doctor Who.
• Frank and Schmidt speculated that artifacts from a past civilization might be found on the Moon and Mars, where erosion and tectonic activity would be less likely to erase evidence.
• The natural fission reactors at Oklo, Gabon, were active some two billion years BP and are mentioned in the paper as an example of detectable ancient nuclear activity.