Alien life may be nothing like life on Earth, so trying to find evidence of their existence requires a bit of creativity.
Scientists only know of one example of life in the universe, and it exists on Earth. But what if life could arise in another way? How to look for aliens if you don't know what they might look like?
It is believed that microbes are probably the most common form of extraterrestrial life because they can arise more easily than larger organisms.
However, it is possible that there is an advanced alien civilization somewhere in space. In either case, these alien species may be unlike anything scientists know about life, Live learning reports.
Since the discovery of the first planet outside our solar system in 1995, scientists have discovered more than 5,000 planets orbiting other stars. Many of these planets are tiny and rocky, like Earth, and lie within the habitable zone of their stars.
This is the region of space around a star where conditions allow liquid water to exist on the planet, supporting life as we know it. There is a good chance that many planets that are not yet known to us have the right conditions for life to emerge.
However, scientists disagree on how exactly to define “life” in relation to living organisms. NASA defines life as “a self-sustaining chemical reaction capable of Darwinian evolution.” This means that organisms with complicated chemical systems that evolve to adapt to their environment.
Life on Earth has evolved over billions of years, from single-celled organisms to gigantic animals and other species, including humans.
Using spectroscopy, a technique for detecting chemical traces of life, scientists look for atmospheric oxygen signatures on other planets that were created by microbes, or chlorophyll signatures that indicate plant life.
But is Darwinian evolution common? What chemical reactions could lead to life beyond Earth?
The universal law of evolution in the Universe
All life on Earth evolved from a common ancestor, the microbe, about 4 billion years ago. The same chemical processes occur in all living organisms on Earth, and they may be universal. But they can also be radically different when it comes to other planets.
In a recent study, an international team of scientists took a different view of evolution. They began to investigate what processes, biological or not, created order in the universe to learn how to study the emergence of life very different from life on Earth.
Scientists believe that complicated systems of chemicals or minerals, placed in an environment that allows some configurations to survive better than others, evolve to store more information. Over time, the system will become more diverse and complicated, acquiring the functions it needs to survive through a kind of natural selection.
Scientists have suggested that there may be a law that describes the evolution of a wide range of physical systems. Biological evolution by natural selection may be just one example of this law.
In biology, information refers to the instructions written in the sequence of nucleotides in a DNA molecule that together make up an organism's genome and shape its appearance and functioning.
From an information theory perspective, natural selection would make the genome more complicated because it would store more information about the environment. However, it would be wrong to say that animals are more complicated than microbes.
Biological information increases with genome size, but the density of evolutionary information decreases. Evolutionary information density is the proportion of functional genes in the genome or the proportion of the total genetic material that expresses adaptation to the environment.
Organisms that humans consider primitive, such as bacteria, have information-dense genomes and therefore appear to be better designed than the genomes of plants and animals.
What could aliens be like?
Scientists have been exploring alternatives to Earth's biochemistry. All known living organisms, from bacteria to humans, contain water, which is the solvent necessary for life on Earth.
But life could potentially arise from other solvents. Scientists have found that such solvents can include sulfuric acid, ammonia, liquid carbon dioxide and even liquid sulfur.
Alien life also cannot rely on carbon, which is the basis of all the basic molecules of life on Earth. Advanced life forms on other planets may be so strange that they are complex to even imagine. That's why scientists have to get original to detect life.
The authors of the study believe that on other planets we should look not only for water and oxygen, but also other substances that may indicate life.
When it comes to developed extraterrestrial civilizations, it is necessary to look for traces of artificial atmospheric pollution or traces of possible technological activity.
Alien life may be very different from life on Earth, but so far scientists have found no evidence that it exists anywhere else in the universe.
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