Humanity has only one example of how life can arise and evolve in the Universe: that of the Earth. No other evidence of life has been discovered outside our planet.
Seen from this point of view, life can take absolutely any shape, some that we would not have even imagined. And then, asks Chris Impey, professor of astronomy at the University of Arizona, whose opinion was echoed by The Conversationhow could you pretend to recognize him?
The questions about how life could develop and evolve in other celestial bodies is one that has fascinated and struck, from ancient thinkers to science fiction writers or astrobiologists today.
More than hypothetical extraterrestrial life forms could take forms that, as I said, no one had considered before. Starting from this observation, a key question implicitly arises: is there a complex biological and physical model that, at least hypothetically, could be universally valid?
Scientists do not have a clear definition of life
Since the discovery of the first planet outside our solar system in 1995, more than 5,000 such planets have been identified to date. And their number grows from one month to another.
Many of them are solid, Earth-like planets that are in the so-called habitable zone. An area located at the optimal distance from a star to allow the existence of liquid water or temperatures that do not go to extremes. In short, the basic conditions for the emergence of life, at least as we know it on Earth.
A simple extrapolation of the number of planets discovered so far indicates more than 300 million possible destinations, out of more than 100 billion solar systems, where a living organism could have been born. And that’s just in the Milky Way. 300 million potential biological experiments, including planets or moons, that could be performed in our lifetime.
However, the uncertainties of astrobiologists start from the very definition of life. A definition that, at least on the surface, should be simple. It is not, and the proof is that scientists have not yet reached an agreement on this point.
Is Darwinian evolution a valid general concept?
If we turn our attention to NASA’s definition of life, “a self-sustaining chemical reaction capable of Darwinian evolution,” we can understand an organism with a complex chemical system that can evolve to adapt to its environment.
In fact, that is exactly what Darwinism advocates. That is, the survival of an organism depends on its ability to evolve to adapt to the environment. And this process is visible and has been demonstrated by scientists on Earth. On Earth, but not elsewhere.
And from there other key questions arise. Can Darwinian evolution be a valid general concept? What are the chemical reactions that can lead to the appearance of terrestrial organisms? Spectroscopy can be an effective method to identify extraterrestrial life, as long as it can indicate the chemical signature of life, but life as on Earth (the oxygen removed by the algae or the signature of chlorophyll, such as and evidence of the existence of the flora)?
Natural selection is only one of the laws that can govern what is alive
Life on our planet began about 4 billion years ago, with a type of unicellular organism (LUCA – last universal common ancestor) which, after the evolutionary process, gave rise to organisms increasingly complex. A process that, among other things, led to our very emergence as a species.
The chemical processes found in all biological forms on Earth are identical, and this might suggest that they are universal. But this is just a misconception. Rather, such processes could be completely different in other parts of the Universe.
In October of this year, many scientists gathered to Carnegie Institution for Scienceof Washington DC The objective was to discover what kind of processes created the order in the universe-biological or not-to understand how to study the emergence of life, using methods different from those of the Earth.
One of the most interesting ideas presented on this occasion was that complex systems of chemicals or minerals, when in environments that allow some configurations to persist better than others, evolve to store larger amounts of information.
As time passes, the system will become more diverse and complex, acquiring the functions necessary for survival through a process reminiscent of natural selection.
In biological terms, natural selection causes a genome to become more complex as it stores more information about its environment.
But complexity is not a sine qua non of evolution, hence the paradox. Organisms that some might consider primitive, such as bacteria, have genomes with a high information density and thus appear to be more efficient in some cases than the genomes of plants or animals.
Researchers have speculated, following this logic, that there could be a law that describes the evolution of a wide range of physical systems. And the conclusion was that biological evolution by natural selection would be just one example of this broader law.
Basically, a universal theory of life is difficult to state. They would include the concepts of complexity and information storage, but would not be related to DNA or the particular types of cells that we find in terrestrial biology.
Alien life remains an elusive mystery
On Earth, the universal solvent is water. All organisms contain water. It is the liquid medium that facilitates the reactions that lead to the emergence of life, but also that maintains it. Hypothetically, however, life can also appear in the presence of other solvents.
Sulfuric acid, liquid sulfur, liquid carbon dioxide, ammonia and others may represent, at least in theory, plausible solvents.
In the same vein, extraterrestrial life could not be based on carbon, a fundamental chemical element in the existence of life on Earth. And so it could be almost, if not completely, undetectable.
A method suggested by scientists would be to identify minerals of biological origin. In our planet, for example, there are thousands of minerals created by biological organisms.
Apatite (calcium phosphate) is one of the most eloquent examples, since it is a crucial element in bones, teeth or scales.
Another approach would be to refer to a possible intelligent civilization. And here we are talking about the so-called techno-signature: artificial lights, industrial pollutants in the atmosphere and so on.
In conclusion, the search for life is a very complex process. And that in terms of life as we know it. If we think about life that we do not know, then things are too unpredictable, and an assumption at this point is practically impossible.
Source: The Conversation
