We, people, are used to taking for granted that we live in sedentary societies, use tools and change the landscape to fit our needs. It is also quite known that in the history of the Earth people are the only people who have developed technology, automation, electricity and mass communications - the distinctive features of industrial civilization. But what if on Earth millions of years ago there was another industrial civilization? Can we find evidence for this in the geological record? Studying the impact of human civilization on Earth, scientists have roughly presented how one could find such a civilization and how this can affect the search for extraterrestrial life.
The study was conducted by Gavin Schmidt and Adam Frank, a climatologist from NASA and an 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 analogs to understand the circumstances under which life could exist in principle. And yet, along with this, we are trying to find a reasonable extraterrestrial life that could contact us. It is assumed that any such civilization should first develop an industrial basis.
This, in turn, raises the question of how often technically advanced civilization can appear. Schmidt and Frank call this the "Silurian hypothesis". Its problem is that humanity is the only example of a developed technically kind that we know. In addition, mankind has been an industrial civilization for the last several hundred years - a tiny drop of time of its existence as a species and a tiny part of the time from the existence of a complex life on Earth.
In the course of his research, the team first noted the importance of the Drake equation. In 1961, astrophysicist Frank Drake developed an equation for estimating the number of developed civilizations that can exist in the Milky Way galaxy. It looks like this: N = R * (fp) (ne) (fl) (fi) (fc) L, the decoding of each variable below. Proceeding from the simplest statistics, it is not difficult to calculate that somewhere there may exist thousands, even millions of alien civilizations:
- R *: rate of star formation in our galaxy.
- fp: percentage of stars with planets.
- ne: the number of terrestrial planets around each star that has planets.
- fl: the percentage of terrestrial planets that have developed life.
- fi: the percentage of planets with life on which intelligent life has developed.
- fc: the percentage of intelligent species that have reached the creation of technologies that can be detected by forces of an external civilization like ours. For example, radio signals.
- L: The average number of years required by an advanced civilization to detect detectable signals.
The Drake equation became the basis for research, and space technologies deepened the knowledge of scientists regarding several variables. But to know the possible duration of existence of other developed civilizations - L - is almost impossible.
In their study, Frank and Schmidt emphasize that the parameters of the equation can change, due to the addition in the form of a Silurian hypothesis, as well as the newest discovered exoplanets.
"If during the existence of the planet on it appeared a lot of industrial civilizations, the value (fc) can be above one. This is a particularly important issue in the field of astronomical observations, which fully defines the first three terms, dependent on astronomical observations. Today it is obvious that most stars have planets. Many of these planets are located in the inhabited zone of the star. "
In short, thanks to improvements in instrumentation and methodology, scientists were able to determine the speed with which stars form in our galaxy. Moreover, recent studies of extrasolar planets have made it possible to estimate the presence of 100 billion potentially inhabited planets in our galaxy. If in the history of the Earth one could find another civilization, this would substantially change the Drake equation.
Then the scientists touch upon the possible geological traces left by the human industrial civilization, and compare these tracks with possible events in the geological record. This includes emissions of carbon, oxygen, hydrogen and nitrogen isotopes, which are the result of greenhouse gas and nitrogen fertilizer emissions.
"Since the mid-18th century, people have thrown more than 0.5 trillion tons of fossil carbon into the atmosphere as a result of the burning of coal, oil and natural gas, far ahead of the natural long-term sources of carbon cycling. In addition, deforestation and carbon dioxide in the atmosphere are spreading due to the burning of biomass. "
Scientists have estimated an increase in sedimentation rates in rivers and sedimentation in coastal environments as a result of agricultural processes, deforestation and digging of canals. The spread of domesticated animals, rodents and other small animals, as well as the disappearance of certain species of animals, is also seen as a direct result of industrialization and urban growth.
The presence of synthetic materials, plastics and radioactive elements (remaining as a result of nuclear energy or nuclear tests) will also remain in the geological record. Radioactive isotopes will be in the soil for millions of years. Finally, one can compare the events of mass extinction in the past in order to determine whether they can be related to the moment of the collapse of civilization. It turns out that:
"The most obvious class of events is the Paleocene-Eocene thermal peaks, which include smaller hyperthermal phenomena, chalk anoxic ocean events and important Paleozoic events."
These events are directly related to the growth of temperatures, the increase in the content of carbon and oxygen isotopes, the growth of sedimentary rocks and the depletion of oceanic oxygen. According to scientists, the events that they considered (hyperthermal), show similarity with the anthropocene imprint (that is, with our era). In particular, the Paleocene-Eocene thermal maximum shows signs that can be related to anthropogenic climate changes.
Most importantly, geological similarities should be considered for the search for anomalies that may be associated with an industrial civilization. Roughly speaking, one can see the trace of another humanity in the geological record. If any anomalies are found, fossils will need to be investigated for the existence of suitable species. However, other explanations of the anomalies are not excluded, for example, volcanic and tectonic activity.
Another important fact is that current climate changes are happening faster than ever. Outside the Earth, this study can help us in finding life on planets like Mars and Venus that could exist there in the past.
"We want to note that there is strong evidence for the presence of water on the surface of ancient Mars and the possible habitability of Venus (due to the darkening of the sun and the atmosphere with low carbon dioxide content), which are 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. "
Two of the most important aspects of the Drake equation, which directly determine the possibility of finding life somewhere in the galaxy, is the huge number of stars and planets, as well as the amount of time that life was allocated to development. Until now, it has been assumed that at least one planet should have given rise to a reasonable 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 the once great inhuman civilization can be right under our feet.
The article is based on materials .
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