Klaus M. Stiefel at his own website:
A hypothesis called “The Silurian hypothesis” wins the title of “most interesting hypothesis most likely to be false” for all of science. In brief, the hypothesis postulates that previously a species different from ours had achieved high intelligence and technological civilization on this planet. The Silurian hypothesis (named after “Silurian” aliens in the brainy British TV series “Doctor Who”) was initially proposed by two astronomers, Gavin A. Schmidt and Adam Frank, as a thought experiment, to see if it would even be feasible to detect the traces of such a hypothetical civilization which had existed many millions of years ago. Would there still be detectable changes in the sedimentation patterns if someone (not human) had built cities and military bases a hundred million years ago? Would ancient trash dumps be conserved somewhere, somehow? Would there be changes in the patterns of radioisotopes in the rocks as a result of an ancient nuclear war?
So, in their original paper, Schmidt & Frank didn’t actually voice belief in an ancient civilization, but pondered the question if and how it would be detectable. They conclude that no ruins of ancient football stadiums, highways or housing projects would survive geological time. In contrast, unusual episodes of global warming and the presence of certain artificial radioisotopes (Plutonium-244 and Curium-247) would give an ancient civilization away. Mass extinctions could be a sign of an ancient smart, technological, fast-expanding species.
More here.
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