Free Astronomy Magazine May-June 2018

ASTROBIOLOGY 39 We know so little about life on Earth before the appear- ance of hominids that there may have even existed in- dustrial civilizations prior to ours without us being aware of them. Now, two scientists propose how to look for the traces of those hypothetical civilizations. If those ancient Terrans respected the ecosystem more than we do, we might never find those traces. W e humans assume that we are the first animal species on our planet to have reached a high degree of technological development, up through becoming an industrial civilization. This be- lief is based on a series of circumstances which at first sight seem to be incontro- vertible. One of them relies on our never having found artifacts and structures in- compatible with the history and prehistory of humanity. Moreover, through the study of fossils, we know, at least roughly, the development of life on Earth, and there re- mains no trace of any species that may have reached a degree of development comparable to ours. But are we really sure that our vision of the past is so comprehen- sive as to rule out the appearance of previ- ous industrial civilizations? Perhaps yes, but the farther we go back in time, the less de- fined the picture of the evolution of life on MAY-JUNE 2018