Introduction
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| Advanced Civilization |
We always talk about extra worlds out there, aliens and how civilizations can sit safely on extra solar planets, protected by the vast distances involved. And it's as if we accept that Earth's nearly five billion years of geological and biological evolution can result in only one dominant form of intelligence: our species.
We, Homo sapiens, as the pinnacle of evolution, are the ultimate, unique and irreplaceable products of a time course aimed at bringing us to dominate this planet... but... what if it really isn't? What if before us ... long ago ... there was a way and time for evolutionary roulette that gave rise to another earthly civilization? Would it really be that far-fetched? After all, complex life has existed on this earth for 500 million years. Can we be absolutely certain that humans are the first intelligent species to have evolved on this planet?
Wasn't there - a Cambrian civilization of intelligent trilobites, underwater cities powered by hydrothermal vents? Or large-brained Cretaceous theropods capable of using tools and language? This is not as absurd as it sounds. On the geological time scale, we have inhabited this planet for only an instant, and industrial civilization has existed for a fraction of that instant. And if humans become extinct tomorrow, the ruins of our society will not last long. But why these questions? And who are the Silurians?
Earth is the only planet known to us where we know for sure that life exists and exists. And it is the only planet that has given birth to at least one industrial civilization, ours, which means by this expression a civilization formed by animals capable of using external sources of energy - such as fossil fuels or solar energy - worldwide. A civilization with such characteristics existed on our planet for more than three centuries, that is, since the industrial revolution provided the means to transform the local economy into a highly integrated system capable of ensuring the mass production of an ever-increasing number of products.
And the ability to change the global environment. As members of the only known industrial civilization, we face alone, at least for now, two infinite immensities: space and time. As far as space is concerned, the exploration of the Solar System by countless probes has produced so much data that we can conclude with reasonable certainty that, at least from here to Pluto, there are no other industrial civilizations (and, for that matter, no signs of life beyond Earth. Outside the Solar System Whether there are other civilizations, we can only imagine, but our ignorance in this matter is complete.
Of course, we know that there are many planets: in almost three decades, thousands have been discovered thanks to the Kepler space telescope and other sophisticated methods of investigation. The extrasolar planets discovered so far Starting from the ratio of the number to the observed total number of stars, we can estimate by statistical methods that there are probably more than 10 billion potentially habitable planets in the Milky Way alone: too many to count. But there's a big problem: they're all out of our reach, and by a lot.
Other Searching the depths of space in search of industrial civilizations is therefore a daunting task, but the same search can be carried out across time without departing from Earth. Ano is equally difficult. We know from the fossil record that complex life forms evolved on our planet beginning 400 million years ago. We also know that evolution does not proceed in a linear fashion, but follows a bumpy path that passes through bursts of life and mass extinctions; We also know that many 'technological' solutions for exploring and manipulating the environment - eyes and wings, for example - have been 'invented' several times over millions of years by completely different species in response to similar evolutionary pressures.
Then there is a question to ask, seemingly bizarre, but entirely reasonable: Is it possible that in the distant past there existed on Earth some other intelligent species that created an industrial civilization somewhat similar to ours? And this question immediately leads to another question: If another industrial civilization ever existed, what geological signs should we look for to prove its existence?
The second question is two scientists, Gavin A. Schmidt, climatologist and director of the Goddard Institute for Space Research and professor of astrophysics at the University of Rochester, directed the work of Adam Frank. The title of the paper with which the two scholars attempted to provide an answer - the Silurian hypothesis..
The Silurian Hypothesis
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| The Silurian Hypothesis |
Refers to an episode of the famous British television series Doctor Who. That episode, dating back to 1970, concerned the discovery of the Silurians, an ancient race of technologically advanced reptilian humanoids that allegedly preceded the advent of humans by hundreds of millions of years. According to the plot, these highly civilized saurians thrived for centuries until Earth's atmosphere entered a period of catastrophic change that forced Homo reptilia to hibernate underground to escape danger.
It should be said at the outset that the two scholars were dealing with entirely theoretical arguments, without even remotely thinking of dressing up as field paleontologists... Schmidt and Frank have found no geological evidence that could be considered proof of the existence of a past industrial civilization; nor do they believe that such a civilization ever existed. However, it is interesting to follow their reasoning and, above all, to reflect with them on the immensity of past geological time and the rapidity with which the traces of civilization such as ours would be eroded and eventually hidden by the uninterrupted reshaping of the earth's surface and ocean floor.
The first footprints of Homo sapiens are still fresh on the earth. Our species dates back about 300,000 years and our industrial capabilities to less than 300. We arrived late on a planet that has orbited the Sun for 4.5 billion years. Enough time, some speculate, for earlier civilizations to have developed and then disappeared without a trace. The bottom line is this: the rocks beneath our feet probably constitute an incomplete encyclopedia of Earth's history. Over the past 2.5 million years, the geological record shows evidence of climate change, different soils, and fragments of older hominid cultures, such as Neanderthals and Denisovans.
But the further we go back in time, the more sparse the physical remains become. All objects belonging to civilizations more than 4 million years old, the evidence suggests, are probably lost forever due to continuous soil remodeling and abrasion by the elements. The built structures we have constructed-highways, railroads, bridges, cities, skyscrapers, dams, etc. - tower mightily before our eyes today; the very surface of the planet appears extensively altered by human activity with effects visible from space, as evidenced by satellite photos of cities illuminated at night by electric lights or those of the millions of km² of land, covered by the geometric grid of cultivated fields.
But the unraveling of all these works on the scale of geological time will occur in roughly the blink of an eye. If the human species were to disappear tomorrow, in less than two million years erosion and sedimentation, acting relentlessly on the currently inhabited territories, would erase any trace of the cities and artifacts produced by industrial civilization. Perhaps only Mount Rushmore, with the faces of American presidents carved in rock, and only the great pyramids of Giza would endure for a fraction of a million years. It follows that the chances of coming across the remnants of an industrial civilization that existed millions of years earlier but lasted only a few thousand years are truly minimal. Should we then resign ourselves to leaving no traces of our existence and being unable to find more in the past? Not exactly.
While it is true that artifacts are deteriorating extremely rapidly and fossils are extremely rare, according to Schmidt and Frank, however, the overall impact of industrial civilization on the planet's climate and mineralogy remains to be examined. Humans are indeed changing the environment through man-made substances, such as plastics. Atomic bombs leave radioactive footprints. Burning fossil fuels is also an obvious chemical sign of industrial activity: it alters the ratio of carbon-13 to carbon-12 in the atmosphere.
Not only that... We know that there was a massive release of carbon into the atmosphere about 56 million years ago, which coincided with a dramatic increase in global temperature and the mass extinction of marine life. Could this be a sign of climate change triggered by an advanced civilization that preceded our own? Probably not... volcanic activity can also produce a similar signature by warming and unlocking carbon-rich ocean sediments; as can the fall of an asteroid... But how to be certain?
The two authors think it would be worth trying to search marine sediments for evidence of short-lived events, but they also admit that this would be extraordinarily difficult at present. In conclusion, the study of sedimentary stratifications provides numerous examples of past epochs in Earth's geological history in which conditions similar to those created by the impact of human industrial civilization on the environment occurred, namely: global increase in temperatures, decrease in the ratio of carbon isotopes, alterations in the nitrogen cycle, anoxia events, deforestation, extinctions, and peaks in the abundance of certain metals.
It follows that the chances of coming across the remnants of an industrial civilization that existed millions of years earlier but lasted only a few thousand years are truly minimal. Should we then resign ourselves to leaving no traces of our existence and being unable to find more in the past? Not exactly. While it is true that artifacts are deteriorating extremely rapidly and fossils are extremely rare, according to Schmidt and Frank, however, the overall impact of industrial civilization on the planet's climate and mineralogy remains to be examined.
Humans are indeed changing the environment through man-made substances, such as plastics. Atomic bombs leave radioactive footprints. Burning fossil fuels is also an obvious chemical sign of industrial activity: it alters the ratio of carbon-13 to carbon-12 in the atmosphere. Not only that... We know that there was a massive release of carbon into the atmosphere about 56 million years ago, which coincided with a dramatic increase in global temperature and the mass extinction of marine life.
Could this be a sign of climate change triggered by an advanced civilization that preceded our own? Probably not... volcanic activity can also produce a similar signature by warming and unlocking carbon-rich ocean sediments; as can the fall of an asteroid... But how to be certain? The two authors think it would be worth trying to search marine sediments for evidence of short-lived events, but they also admit that this would be extraordinarily difficult at present. In conclusion, the study of sedimentary stratifications provides numerous examples of past epochs in Earth's geological history in which conditions similar to those created by the impact of human industrial civilization on the environment occurred, namely: global increase in temperatures, decrease in the ratio of carbon isotopes, alterations in the nitrogen cycle, anoxia events, deforestation, extinctions, and peaks in the abundance of certain metals.
However, none of these geological traces can be considered conclusive evidence for the existence of an ancient and vanishing industrial civilization. Indeed, there is no way to prove through the study of sediments that past climatic changes, of which there is also clear evidence, were as rapid and sudden as those caused by human industrial activities. Moreover, there is also to be considered that any culture sophisticated enough to become industrialized may eventually have harnessed entirely natural energies, such as the power of wind, waves, or the sun. And herein lies a paradox: today we know that our species is altering the environment, but we also know that we are working to mitigate the effects of our presence on the planet.
This amounts to saying: the more civilization progresses on the path of environmental awareness, the less garbage it will leave around until it becomes completely invisible to the eyes and tools of later civilizations. Frank and Schmidt-we have already said this-do not believe that such a civilization ever existed, but their article asks a broader question that is also relevant to exoplanet studies. Indeed, only by asking these kinds of questions will we be able to gain the knowledge that in the future (or already in the present, with the James Webb Telescope) will allow us to pick up on the fly signs of the existence, present or past, of some kind of alien civilization.
There is, however, one aspect we have not yet considered in the Silurian hypothesis. What if a remote terrestrial civilization - reptilian or otherwise - had acquired a level of technology that would allow it to fly in space? Should that be the case, it is more likely that we could find traces of its very distant past, not on Earth, but rather on other nearby celestial bodies: the Moon, and Mars--all worlds on which tectonic and erosion phenomena are much less present. Remember the black monolith discovered on the Moon inside the Tycho crater? That's it-something like that. Again, that was literature, but let's remember that Arthur Clarke, the author of 2001: A Space Odyssey, was someone who never missed a prediction...