Aliens and the shadow biospheres
During the summer of 1950, Enrico Fermi, one of the fathers of the atomic age, together with his friends Edward Teller, Emil Konopinski, and Herbert York, were walking in the hot New Mexico sunshine on their way to lunch in the Los Alamos Laboratory cafeteria. Coincidentally, the conversation that day touched on the subject of flying saucers, and according to Teller, the chat was rather brief and superficial on a topic only vaguely related to space travel. One of them had recently seen a cartoon in The New Yorker depicting aliens intent on stealing garbage cans, and so they discussed the obviousness of flying saucers not being real.
The exchange of views invariably trespassed for a time into the meanderings of mathematics, when at one point, as Konopinski recalls, Fermi surprised them with the question
"But where is everybody?"
His perhaps somewhat naive way of putting it triggered some hilarity among those present, even though it was clear that the subject was extraterrestrial life, and according to York, he went on to make a series of calculations on the probability of the appearance of human life, the likely emergence and duration of advanced technologies, and so on, concluding on the basis of those calculations that the possibility of intelligent civilizations close to us could be very high and that we have probably been visited by aliens long ago and for many times to come. This informal conversation was the basis on which the famous Drake equation was later constructed, an experiment speculative conceptual on statistics that attempts to mathematically explore the probability of intelligent alien life in this part of the universe and at this time in history. Of course, the "real" solution to the Drake equation is not the answer itself; rather, the questions it may generate in attempting to solve it are.
Fermi and his friends ventured some plausible answers to the fateful question, e.g., the enormous distances of space would frustrate any sort of interstellar travel, and even when that were possible, it might not be worth the effort to achieve it (except, as is speculated today, using robotic or even generational probes or ships, assuming that the alien lifespan is as short as ours or that they necessarily have to die as it happens on this planet), or again that advanced civilizations might not survive long enough to reach the level of technology sufficient to take off to perform interstellar travel. Since then there have been countless attempts to come up with strange, new solutions to the ambiguous paradox, some becoming best sellers such as the essay by Stephen Webb, Theoretical Physicist and Collector of Solutions to the Fermi Paradox, translated into Italian as "If the Universe is Teeming with Aliens... Where Are They All?"
Of course, any solution is limited by knowledge acquired and by our ability to theorize, albeit with all the abstractions that are granted to us by our enormous cognitive limitations or misled by what we take for granted based on anthropic principles or similarities with the only life forms we know, namely terrestrial ones). The question, however, cannot be deprived of all sorts of complexities, and there is no doubt that life-related research has always captivated science from different perspectives.
In the 1950s Miller and Urey attempted to reproduce the conditions that led to the formation of the first organic molecules that form the basis of life; today Craig Venter tries to build synthetic life forms, and at the same time space is being scanned by physicists and astrobiologists looking for an echo of life. But for some, to answer the question "are we alone in the universe?" one would not have to look too far. In extreme environments such as ocean floors, polar ice, or arid deserts might hide life forms that have evolved independently and alternatively to our own, life forms that have so far gone unnoticed, a kind of "shadow biosphere" populated by microbial organisms whose existence would testify that life on our planet would have had different and multiple beginnings, following independent paths and parallel evolutionary trees, although our polyphyletic course eventually prevailed by suffocating the others and preventing them from evolving, so much so that we are convinced that on Earth, carbon-based life forms are not only the only ones that exist, but even the only ones possible in the Universe, and it is these forms that, naively, perhaps even with humanoid features, we yearn to find for the infinite cosmos.
For more than 50 years, in fact, scientists have been sifting through deep space in search of extraterrestrial life forms, though admittedly without much success: neither programs involving the use of radio telescopes nor missions to Mars so far in fact have been able to detect much of anything.
However, at this point, notwithstanding our limited scope of inquiry, an inevitable thought arises, namely that perhaps we need to set aside the theory that an unlikely E.T. in our own image, if only behavioral, if not even pathetically aesthetic or biological, is sending us messages from space to interrelate with us. Continuing to scan space for alien life forms is probably just a waste of time, and perhaps we would be better off focusing on the extraterrestrials that already populate our planet.
Philosophy professor Carol Cleland and her colleague Shelley Copley coined the term "shadow biosphere" in this regard in 2005, which later appeared in a 2006 article in the International Journal of Astrobiology to describe possible invisible life on our planet. To be precise, shadow biosphere means a hypothetical microbial biosphere of the Earth that uses radically different biochemical and molecular processes from those of life currently known. Although life on Earth is relatively well studied, the shadow biosphere may still have remained unknown, due to the exploration selective of global microbial targets, primarily the biochemistry of macro organisms.
On Earth then, we could theoretically co-habit unbeknownst to us with microbial life forms with completely different biochemistry than those shared by life as we know it today. This theory, far from being some vulgar and unfounded cryptozoology, is supported by many other scientists, including astrobiologists Chris McKay of NASA's Ames Research Center and distinguished theoretical physicist and Arizona State University astrobiologist Paul Davies.
If it turned out that we failed to realize that we shared a planet with
these shadow life forms for eons, despite all the scientific advances of the 19th and 20th centuries, then we may need to honestly rethink how we go about searching for life on other worlds. Space robots-such as the Mars rover Curiosity, for example-are certainly sophisticated. But what chance do they have of detecting alien entities if the laboratories of modern science scattered to the four corners of the globe have not yet spotted them on our planet?
Life as we know it, unfortunately, is what astrobiologists look for in the search for extraterrestrial life, with the naiveté and tenderness typical of our species that feels so alone in the world without other sentient life forms with which it can compare itself. But if an alternative form of life were discovered on Earth, it would undoubtedly have an impact on the search for life on other worlds, whatever they may be.
It certainly cannot be denied, in fact, that it is much easier to search for it on Earth than it is on Mars, having all kinds of instruments and technologies available for the search, while we have to instead specifically design them and drag them to Mars in search of hypothetical life forms that are completely unknown. So if there is a possibility that such life exists on Earth, theoretically - and there is no reason at this time to rule it out - then it makes much more sense, and is much more likely to be detected here on Earth. The problem, of course, is that the presence of life existing here on Earth is so strong that we have to figure out the way to recognize the unknown life and separate it from the known life, which can confuse and mask its traces. And this is certainly the really difficult part. Scientists have proposed possible methods for detecting this weird life, but until it is detected, the shadow biosphere will remain just an interesting theory.
Therefore, finding extraterrestrial life forms on Earth would certainly be the best evidence of their existence outside our planet. Paul Davies, is in fact convinced that "strange microbes" belonging to a different tree of life might already be present in some isolated ecological niches where ordinary life could hardly take root or survive, such as arid deserts, undersea volcanoes, saturated salt lakes or the dry valleys Antarctica. Some research groups have already initiated such studies in arsenic- contaminated localities, such as Mono Lake in California. A life form with arsenic or phosphorus as its base therefore is not to be ruled out, nor is it any less viable than those with carbon as their base to which we have become accustomed and from which we have evolved and selectively diversified along our predominant evolutionary tree.
The shadow biosphere thesis, however, does not convince all scholars.
"This is just science fiction, I prefer to believe in the scientific evidence"
commented Colin Pillinger who headed Beagle 2, the space mission that was supposed to reach Mars to discover new traces of life and yet all traces of which have been lost. According to Pillinger, the red planet remains the best destination for discovering the existence of alien life forms. Which not everyone agrees with, however, since the moons of our Solar System, e.g., Europa, Enceladus or Titan, certainly offer better possibilities and hope than a dead planet like Mars, which, if any biotic evolution has ever had, by now this has probably disappeared forever, along with its oceans and atmosphere, and well may give us only fossil evidence of these past events, which - and this would certainly be interesting, forcing us perforce to rewrite the origin of life in the solar system - we could not rule out that they even contributed to an exchange of organic or biological material, when Mars and Earth were subjected to such intense meteoric bombardment that life was wiped out several times and/or hurled from one planet to another. In that case on Mars we might fantasize about finding fossil traces of our ancestors or carbon-based precursors far less alien and more related to us Earthlings than we had hoped, if not vice versa (in fact, there is nothing to prevent us from thinking that terrestrial biochemical samples ended up on Mars giving rise to a more unfortunate and less enduring parallel evolution).
However, going back with our feet on our planet and leaving aside these suggestive theories, plausible, to be sure, but all to be proven, until now it had always been believed that the building blocks with which all biological organisms on Earth are constructed are only six: the elements carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur, or the so-called CHONPS, from the acronym the Anglo-Saxons use. However, a team, led by Felisa Wolfe Simon of the U.S. Geological Survey, is investigating the possibility that places heavily contaminated with arsenic, such as Mono Lake in California, could support life forms that use arsenic in the same way that life in other forms uses phosphorus. In fact, in this lake researchers have found a type of bacterium that, if you change its "diet," replacing phosphorus with arsenic, not only does not die, but is able to use the element, which is toxic to us, as a spare part.
And, mind you, this is not simply of an exotic process of metabolism. No, the bacterium actually uses arsenic instead of phosphorus as a building block. To understand, phosphorus is an essential element of the DNA and RNA chains as well as the proteins. This discovery thus shows that it is possible, absence elements that in the of the constitute Earth, to make use of a different kind of biochemistry to support life processes. Sort of like in the science fiction classics where you discovered life forms based on silicon instead of carbon (e.g., the Horta from Star Trek).
Steven A. Benner, Alonso Ricardo and Matthew A. Carrigan, biochemists at the University of Florida, have argued that if RNA-based organisms once existed, they may still be alive, but have gone unnoticed because they do not contain ribosomes, which are usually used to detect living organisms. They suggest they therefore look for them in low-sulfur environments, spatially constrained environments (e.g., minerals with pores smaller than a micrometer), or environments with cycles between extreme heat and cold, there where the classical organic life known to us, which is more efficient in all other environments, could not take root and thus compete evolutionarily with them.
Other proposed candidates for a shadow biosphere include organisms using different pools of amino acids in their proteins, or different molecular units (e.g., bases or sugars) in their nucleic acids, or an opposite chirality (spatial molecular specularity) of ours, or using some of the standard non-amino acids, as well as, as mentioned above, the use of arsenic instead of phosphorus.
Ultimately, the discovery is important for two reasons. The first is that it expands the definition of life, making it more flexible and increasing the likelihood of finding it even in environments that would previously have been thought hostile. But, perhaps more importantly, because it could be a clue in favor of a suggestive theory: the one that, even on our Earth, the origin of life would not have been a unique phenomenon, but would even have been repeated several times in different forms, possibly obliterated by catastrophic events such as collisions with celestial bodies or volcanism and selected by the competition among these varied attempts that life made before it asserted itself overwhelmingly with organic molecules that include carbon. It is only a hypothesis, of course, but we could first life on or then discover here among us life forms based on entirely new and different biochemical processes.
Such a discovery, if and when made, would force us to conclude that, in a sense, aliens are already among us. Little consolation perhaps, since we have a need to stop feeling alone and to confront other sentient and intelligent life forms, otherwise we might as well just interact with the other living beings who share with us this difficult evolutionary path from which we were born (and many tragic extinctions), but if nothing else less foolish and risky than sending random signals and probes to other hypothetical alien life forms we know nothing about, showing them the way to a habitable and resource-rich planet that might appeal to many and against which we might have no defense. Indeed, we must not and cannot forget that life is first and foremost a struggle for survival, predation, competition or "law of the jungle" as we want to call it. So let us leave naive handshakes filled with beautiful hopes and ethical principles and brotherhood between ETs and humans to science fiction. If we have mirror neurons that cause us to turn the other cheek and sacrifice for others by helping each other, it is not necessarily the case that elsewhere in the cosmos sentient beings have evolved in the same way.
On the contrary, here on Earth, among billions of current and extinct life forms, this strange mutation seems to have only few species of the Primate order (and it has not even succeeded that well, as so many horrors and genocides unequivocally demonstrate). Other living things prey on each other both in the oceans and on the landmasses without much ado. Let statistics at least knock some sense into us before we shoot radio waves and gold plates out of the Solar System aboard insulting probes with pulsar maps to better track us along with meaningless friendship messages. But before making a such a thing severely affecting the entire human race, couldn't a planetary referendum be held, or as usual those with the money to launch missiles into space rule and everyone else must submit to the wretched choices of a few?
Let us console ourselves, then, that the signals fortunately dissipate with the square of distance until they become incomprehensible and indistinguishable from the cosmic background radiation, and that the laws of probability over billions of light-years of near-infinite vacuum play in our favor. In all probability, we will be alone until our extinction. So let us hold tightly to this beautiful planet and all it contains, for truly it is all we have, learning to respect every life form that has as much right as we do to exist, facing this journey together, wherever it may take us.
