Explainer: Silurian Hypothesis and the possibility of previous life-forms on earth

By Prarthana Mitra

The search for intelligent alien life has fuelled numerous ground-breaking research and space missions over the past few years. But, should we only be looking to outer space in our hunt for other intelligent life forms? Could it be possible that the Earth was once also home to another intelligent species, way before humans even existed?

In a speculative paper, two science fiction aficionados consider the implications of intelligent life-forms existing on earth before human beings came along. This new study by climatologist Gavin Schmidt, and physicist Adam Frank sets out to prove the existence of intricate and advanced civilisations, not in outer space, but in your terrestrial prehistoric backyard.

Here’s what happened

Schmidt and Frank, both of whom are Doctor Who fans, co-authored a paper called “The Silurian Hypothesis”, borrowing the titular epithet from the reptilian species in the popular BBC show. Basing their paper on the fictional Silurians that inhabited earth before the dawn of human history, the study attempts to discover possible industrial civilisations in the geological record. Baffled by the sheer amount scientific effort put in the detection of extra-terrestrial life, Schmidt thinks it is more probable to find evidence of life in earth’s “deep past”, given that it has existed for 4.5 billion years in the solar system.

Looking for evidence

The new study, which has been published this month’s edition of the International Journal of Astrobiology, will make use of the projected footprint of the Anthropocene—which is a proposed era dating from the time humankind began impacting the Earth’s geology and ecological system. The study will therefore, take into account man’s role in the biological, geological and climatic activity, in order to shed light on the future of human civilisation.

To provide further context, perspective, and a larger picture of the cumulative effects of anthropogenic activities, Schmidt and Frank will also analyse the geological record for signs of any Silurian precursors on earth.

Besides the search for “byproducts of fossil fuel consumption, mass extinction events, plastic pollution, synthetic materials, disrupted sedimentation from agricultural development or deforestation, and radioactive isotopes potentially caused by nuclear detonations”, the Silurian hypothesis will also draw from the Drake equation, “a probabilistic approach to estimating the number of intelligent civilisations in the Milky Way, developed by astronomer Frank Drake.”

Why you should care

“My world, my Earth is a ruin. A planet spoiled by the human species. We multiplied and fought and gobbled until there was nothing left, and then we died. We controlled neither appetite nor violence; we did not adapt. We destroyed ourselves. But we destroyed the world first,” said the renowned American author, Ursula K. Le Guin.

Science fiction is replete with examples of ancient life forms who have built complex civilisations on Earth, but have nonetheless succumbed to extinction. What can conclusive proof about prior intelligent life-forms on earth, teach the present civilisation about adapting, and protecting the only known planet capable of sustaining life in the solar system? Will pre-historic revelations in anthropology halt our march towards a similar extinction? Will archaeological evidence serve as a reminder for us to stop turning the Earth into an uninhabitable wasteland?

“It might be [that] the detectable period of a civilisation is much shorter than its actual longevity, because you can’t last a long time doing the kinds of stuff that we’ve been doing,” Schmidt said. “You either stop, because you’ve messed it all up, or you learn not to do it. Either way, the burst of activity, wastefulness, and massive footprints is actually a very short amount of time.”