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39 JULY-AUGUST 2022 ASTRO PUBLISHING Suppose, however, that hu- manity comes to its senses as soon as possible and is able to fully exploit the vital time span that the Sun guarantees to the Earth, then another 1-2 bil- lion years. Today, as well as in that distant future, L t remains smaller than L b because both are linked to a specific planet, on which biology has a much longer history than technology. Long before the Sun, in its red giant phase, engulfs the Earth, humanity will have already moved elsewhere, and hav- ing an almost infinite future ahead, it could happen that at some point L t becomes greater than L b . It can be deduced that if technosignatures are not al- ready in excess compared to biosignatures today, they will probably be in the future. Anyway, we cannot rule out that humanity as a whole be- comes so stupid as to annihi- late itself, unleashing a nuclear war, creating lethal viruses or irreparably compromising the ecosystem. If this happens within a very short geo- logically time, another technological civilization could evolve after a pause of a few million years, a new civilization that would still have an im- mense time at its disposal to spread its technology throughout the galaxy, hopefully without making the same mistakes as ours. Curiously, just as we can- not quantify the L t /L b ratio for the future, we cannot quantify it for the past. In fact, although our civilization is having an indelible impact on geo- logical records (in a word: Anthropocene), in mil- M anasvi Lingam is a member of the De- partment of Aerospace, Physics and Space Sciences, Florida Institute of Technol- ogy. [Photo by Mia B. Frothingham] S ofia Z. Sheikh is an NSF-ASCEND Postdoctoral Fellow at the SETI Institute, working on techno- signature searches with the Allen Telescope Array. R avi Kumar Kopparapu is a re- search scientist at NASA Goddard Space Flight Center, Greenbelt, MD. The arbitrary average value initially attributed to L c was around 10,000 years, perhaps even optimistic con- sidering that the apex of the so- called “Cold War” was reached at the very beginning of the 1960s, when the use of nuclear weapons seemed close. After 60 years, the same scenario and threat has re- turned, “enriched” by a pandemic and the beginning of a climatic up- heaval, whose developments we can- not predict. These are just some of the threats that, in extreme cases, could plunge humanity to a pre-tech- nological level. Fortunately, there are no concrete reasons to believe that our civilization is representative of all possible alien civilizations ex- isting in the galaxy. If there are oth- ers, they could aspire to longevity im- measurably greater than ours. lions of years the causes of the changes we are responsible for will not be distinguishable from the ef- fects of natural processes and phe- nomena. If there had existed on Earth a technological civilization be- fore ours, perhaps tens of millions of years ago, the chances of finding di- rect evidence of its passage would be feeble. We would be more likely to detect indirect evidence, such as anomalies in the chemical composi-