If an industrialized civilization had existed on Earth many millions of years before our era, what traces would it have left and would they be detectable today? That is the unheard-of premise that led Adam Frank, an astrophysicist at the University of Rochester, and Gavin Schmidt, director of the NASA Goddard Institute, to write an article in 2018 in which they proposed what is known as the Silurian Hypothesis. .
The term Silurian Hypothesis was inspired by an episode of the television series Doctor Who in which intelligent reptiles appeared, and the study was published in the International Journal of Astrobiology .
In the article, both scientists wondered how the existence of a civilization older than ours several million years could be detected. Fossilization is a relatively rare process, otherwise we would be finding dinosaur fossils day in and day out. This, together with the fact that the earth's crust is renewed and modified due to tectonic activity, and that very little of the current surface was exposed before the Quaternary, makes it very difficult to find physical traces or direct remains of a possible civilization of such antiquity.
Therefore, his conclusion is that it is most likely that we would find indirect evidence, such as anomalies in the chemical composition or in the ratio of isotopes in the sedimentary layers, due to the use of fossil fuels and nitrogen-based fertilizers, for example, which may be detectable in the fossil record for eons.
As for the objects that could indicate possible evidence of past civilizations, there would be plastic waste and nuclear waste, buried deep in the subsoil or on the ocean floor, which would make them very difficult to find. It would be easier if these civilizations had gone into space and left artifacts on the Moon or Mars, where they would be easier to find due to less erosion and tectonic activity.
Of course, both authors are aware that what they are proposing is highly unlikely:
Frank and Schmidt end their article stating that:
As an experiment, it is an interesting hypothesis, but only that, because today there is no evidence of catfish or other intelligent beings before us, humans, on planet Earth.