Free Astronomy Magazine May-June 2018

41 MAY-JUNE 2018 ASTROBIOLOGY have left behind traces of other kinds, such as artifacts and different types of struc- tures. However resistant these traces might be, the researchers who deal with these topics agree that even the most enduring evidence vanishes within 100-200 million years due to the actions of the geologic, hydrologic and atmospheric activity of our planet. Moreover, even if an industrial civ- ilization prior to ours had appeared in times closer to ours (for example, between 10 and 100 million years ago) and had urbanized the planet for an extension comparable to what we have put in place, any traces would be dispersed over less than 1% of the Earth’s surface, and probably buried at great depths. Discovering direct evidence of an industrial civilization that existed tens or hundreds of millions of years ago would, therefore, re- quire a great deal of luck due to the lim- ited spatial (and perhaps even temporal) distribution of those very ancient remains. If, however, that civilization had reached a level of industrial development compara- ble to ours, it would have altered and pol- luted enough the environment to leave a perhaps recognizable mark in the sedimen- tary rocks. This possibility has been addressed for the first time by Gavin Schmidt (NASA Goddard Institute for Space Studies) and Adam Frank (Department of Physics and Astron- omy, University of Rochester) in a work re- cently published in the International Jour- nal of Astrobiology with the title “The Sil- urian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?” Before briefly examining the interesting arguments of the two authors, we an- ticipate an easy misunder- standing by noting that the name of the hypothe- sis does not refer to the Silurian period (about 444- 420 million years ago), but derives more trivially from an episode of the TV series Doctor Who, in which an ancient civilization was awakened by human ex- periments with a nuclear reactor. The study, there- fore, does not want to suggest that a civilization may have existed in the Silurian period. That said, the Silurian Hy- pothesis of Schmidt and Frank indicates a reasonable way to follow in the search for a hypothetical industrial civilization prior to ours, and does so con- sidering essentially geochemical factors, namely the presence of certain isotopes and their abundances in the geological lay- ers, the presence of synthetic materials and elements, as well as the presence of struc- tural alterations of their ancient territories due to its intensive exploitation. Today, we are sure to have changed the ecosystem so much as to start a new geo- logical age, which since the 80’s has been referred to as the Anthropocene (the last three centuries of the Holocene, character- ized by industrialization). I f a civilization really existed between the Pa- leocene and the Eocene, it had to compete with rather worrying fauna. One exam- ple is the Dia- tryma Gigantea, a huge carnivorous bird 2 meters tall and a hundred kilograms heavy, which hunted in Europe and North America.