We humans are accustomed to taking it for granted that we live in sedentary societies, use tools, and change the landscape to fit our needs. It is also well known that in the history of the Earth, people are the only ones who developed technology, automation, electricity and mass communications - the hallmarks of industrial civilization. But what if there was another industrial civilization on Earth millions of years ago? Can we find evidence of this in the geological record? Studying the influence of human civilization on Earth, scientists have roughly imagined how such a civilization could be found and how it could affect the search for extraterrestrial life.
The study was conducted by Gavin Schmidt and Adam Frank, NASA climatologist and astronomer at the University of Rochester, respectively.
As they note in their study, the search for life on other planets often requires a search for terrestrial analogues in order to understand under what circumstances life could exist in principle. And yet, along with this, we are trying to find intelligent extraterrestrial life that could contact us. It is assumed that any such civilization must first develop an industrial base.
This, in turn, raises the question of how often a technically advanced civilization can emerge. Schmidt and Frank call this the "Silurian hypothesis." Its problem is that humanity is the only example of a technically advanced species that we know. Moreover, humankind has only been an industrial civilization for the past few hundred years - a tiny drop of its lifetime as a species and a tiny fraction of the time from the existence of complex life on Earth.
In their research, the team first noted the importance of the Drake equation. In 1961, astrophysicist Frank Drake developed an equation to estimate the number of advanced civilizations that could exist in the Milky Way galaxy. It looks like this: N = R * (fp) (ne) (fl) (fi) (fc) L, the decoding of each variable is below. Based on the simplest statistics, it is easy to calculate that there may be thousands, even millions of alien civilizations somewhere out there:
R *: The rate at which stars form in our galaxy.
fp: Percentage of stars with planets.
ne: the number of terrestrial planets around each star that has planets.
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fl: Percentage of terrestrial planets that have evolved life.
fi: The percentage of planets with life on which intelligent life has evolved.
fc: The percentage of sapient species that have made it to technology that can be discovered by forces of an external civilization like ours. For example, radio signals.
L: the average number of years it takes an advanced civilization to detect detectable signals.
Drake's equation has become the basis for research, and space technology has deepened the knowledge of scientists about several variables. But to find out the possible duration of the existence of other advanced civilizations - L - is almost impossible.
In their study, Frank and Schmidt emphasize that the parameters of the equation may change, thanks to the addition in the form of the Silurian hypothesis, as well as the newest discovered exoplanets.
“If during the existence of the planet, many industrial civilizations appeared on it, the value (fc) may be higher than one. This is a particularly important question in the field of astronomical observation, which completely defines the first three terms dependent on astronomical observations. It is obvious today that most stars have planets. Many of these planets are located in the habitable zone of the star."
In short, thanks to improvements in instrumentation and methodology, scientists have been able to determine the rate at which stars are forming in our galaxy. Moreover, recent studies of extrasolar planets have estimated the presence of 100 billion potentially habitable planets in our galaxy. If another civilization could be found in the history of the Earth, it would significantly change the Drake equation.
Scientists then raise the question of possible geological footprints that human industrial civilization leaves, and compare these footprints with possible events in the geological record. This includes emissions of isotopes of carbon, oxygen, hydrogen and nitrogen, which are the result of emissions of greenhouse gases and nitrogen fertilizers.
“Since the mid-18th century, humans have emitted more than 0.5 trillion tons of fossil carbon from the burning of coal, oil and natural gas, far ahead of natural long-term sources of carbon cycling. In addition, deforestation and carbon dioxide are spreading in the atmosphere due to the burning of biomass.”
Scientists have estimated increases in sedimentation rates in rivers and sedimentation in coastal environments as a result of agricultural processes, deforestation and canal digging. The spread of domesticated animals, rodents and other small animals, as well as the disappearance of certain animal species, are also seen as a direct result of industrialization and urban growth.
The presence of synthetic materials, plastics, and radioactive elements (left over from nuclear power production or nuclear testing) will also remain in the geological record. Radioactive isotopes will be in the soil for millions of years. Finally, one can compare events of mass extinction in the past to determine if they may be associated with the moment of the collapse of civilization. It turns out that:
"The most obvious class of events is the Paleocene-Eocene thermal maximum, which includes smaller hyperthermal events, Cretaceous anoxic oceanic events, and significant Paleozoic events."
These events are directly linked to rising temperatures, increasing levels of carbon and oxygen isotopes, the growth of sedimentary rocks, and the depletion of ocean oxygen. According to scientists, the events that they considered (hyperthermal) show similarities with the Anthropocene imprint (that is, with our era). In particular, the Paleocene-Eocene thermal maximum shows signs that can be associated with anthropogenic climate changes.
Most importantly, geological similarities should be looked at for anomalies that may be associated with industrial civilization. Roughly speaking, one can discern a trace of another humanity in the geological record. If any anomalies are found, the fossils will need to be examined for the existence of suitable species. However, other explanations for the anomalies are not excluded - for example, volcanic and tectonic activity.
Another important fact is that the current climate change is happening faster than ever before. Outside of Earth, this exploration could help us find life on planets like Mars and Venus that might have existed there in the past.
“We want to point out that there is strong evidence for surface water on ancient Mars and possible habitability for Venus (due to the darkening of the sun and a low carbon dioxide atmosphere), supported by recent simulations,” the scientists note. “Therefore, deep drilling in the future will allow us to touch the geological history of these issues. Perhaps we will find traces of life or even organized civilizations."
The two most important aspects of the Drake equation that directly determine the possibility of finding life anywhere in the galaxy are the huge number of stars and planets, as well as the amount of time that was allotted for life to develop. Until now, it was assumed that at least one planet should have given rise to an intelligent species that will learn to create technologies and communications.
But there is a possibility that civilizations in the galaxy have already been and still will be, not necessarily existing now. Who knows? The remains of a once great inhuman civilization may be right under our feet.
Ilya Khel