Free Astronomy Magazine May-June 2018

42 MAY-JUNE 2018 ASTROBIOLOGY A funny scene of life of a hypothetical civi- lization of sauri- ans that “existed” no less than 100 million years ago. [University of Rochester illus- tration/Michael Osadciw] In the graph be- low (which shows the curve of the 18 O/ 16 O isotopic ratio over the last 65 million years), the ar- rows indicate rapid periods of global warming. The most inter- esting seems to be the one called PETM. [Zachos et al., Nature] ters the balance between some elements that make up atmospheric gases. A similar effect, though less dramatic, may come from the agricultural exploitation of the land and the systematic use of fertilizers. The continuation of all these activities over time generates anomalies in the abun- dances of the isotopes of carbon, oxygen, hydrogen, and nitrogen, and in the amount of greenhouse gases that derive from these elements, such as carbon dioxide, methane and nitrous oxide. The impact of human activity on the natural equilibrium of the planet has been so sig- nificant that if our civilization died out in a relatively short time, and a similar one were to appear after millions of years, the geol- ogists of the latter could distinguish in the sedimentary rocks the corresponding layer to the Anthropocene, and perhaps under- stand that at that time the planet was dom- inated by an irresponsible civilization. According to Schmidt and Frank, we could do the same thing in the search for ancient civilizations today, and we’ve only to real- ize for what and where to look. By exclud- ing possible randomly and inhomoge- neously scattered traces, it may be more profitable to look for markers scattered more or less uniformly across the globe. However far from each other two indus- trial civilizations may be in time (and also in space), they have one thing in common: they consume energy. On Earth, the most widespread and easy- to-find sources of energy are wood and fossil fuels; it is therefore very probable that a very ancient industrial civilization may have done what we still do today: burn wood, coal, oil and natural gas to move machines and produce heat. As we all know, in the long run, this solution al-