Free Astronomy Magazine November-December 2020

28 NOVEMBER-DECEMBER 2020 ATMOSPHERIC POLLUTION and fossil fuels considerably in- creased the presence of carbon dioxide and sulfur dioxide in the at- mosphere. All the molecules produced in large quantities by human activities in the last two and a half centuries would be clearly visible in the light of our planet collected and ana- lyzed by an observer placed at a maximum distance of about 250 light years. Within this radius there are at least 200,000 stars, some of which could host planets suitable for the development of life. Even with a strict selection, for ex- ample considering only solar-type stars with an age of not less than four billion years, there would still be thousands of targets to be explored with specific SETI pro- grams. Undoubtedly, the last two and a half cen- turies of industrialization have strongly character- ized the Anthropocene, but minor and more local- no doubt that, from planets a few tens of light years away, anomalous abundances of (for example) benzene, toluene, nitrogen oxides, carbon monoxide, carbon dioxide, methane and various metals would be eas- ily distinguishable. Some of these elements and chemical compounds began to be mas- sively released into the atmosphere start- ing with the first Industrial Revolution, begun in England in 1760 and driven by the improvement of the steam engine. In- evitably, the growing demand for wood I mpressive im- ages that testify to the appalling air pollution that oppressed large urban centers in the first decades of the Industrial Revolution. About 200 light years from Earth, the traces of this scenario are certainly recog- nizable.