The Silurian Hypothesis

The Silurian Hypothesis

One of the benefits of working for NASA is that the enormous range of science the agency covers – from satellite records for the present day, to exoplanet climates, from early Mars and deep time on Earth to the far future – and the opportunity to think ‘big’. This week sees the publication of a paper I wrote with Adam Frank that we hope might provoke some ‘big’ thinking.

The Silurian Hypothesis (preprint) is the idea if industrial civilization had arisen on Earth prior to the existence of hominids, what traces would be left that could be detectable now? As a starting point, we explore what the traces of the Anthropocene will be in millions of years – carbon isotope changes, global warming, increased sedimentation, spikes in heavy metal concentrations, plastics and more – and then look at previous examples of similar events in the geological record. What is unique about our presence on Earth and what might be common to any industrial civilization? Can we rule out similar causes?

(Dino Street (University of Rochester illustration/Michael Osadciw)

Adam had a nice piece in the Atlantic and there is also a good write up on Motherboard.

The naming of this idea comes from a 1970 Dr. Who episode where an ancient race of reptilians (“Silurians”) who had put themselves in hibernation to avoid a global catastrophe were awakened by experimental nuclear physics experiments. (I tried to find ‘prior art’ on pre-human terrestrial civilization that wasn’t based on notions of panspermia or ancient astronauts, but I haven’t yet been successful – anyone?). Needless(?) to say, we aren’t proposing any such occurrence (not least because the Silurian period is too early for the development of complex life on land).

The ideas in the paper lead naturally to many lines of speculation, some of which are relevant to us today, and some of which are just interesting (to us at least). For instance, given that the more sustainable a civilization is, the smaller its geophysical footprint might be, what does that imply for the detectability of long-term civilizations? Does the onset of ocean anoxia at the end of many of these events suggest a possibility of cycle where the collapse of one civilization provides the seeds (fossil fuels) for the next?

The whole idea is so intriguing that I wanted to do more with it than is possible in a journal article. Other scientists have occasionally dabbled in science-fiction (notably Carl Sagan and Fred Hoyle) and so, following their lead, I wrote a short story “Under the Sun” about the consequences for finding such a signal.

Literary as well as scientific criticism welcomed!


  1. G.A. Schmidt, and A. Frank, “The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological record?”, International Journal of Astrobiology, pp. 1-9, 2018.

Superforest,Climate Change

via RealClimate

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