Often you can find messages like "astronomersbelieve that life could exist on planet xxx ”or“ in order to find life, you first need to detect signs of water ”and so on. But what do they mean by "life"? Anything that can only breathe? Or eat? Or should it necessarily move? We don’t really think when we are asked to distinguish between living and nonliving: a person is alive, a cat is alive, a closet or a machine is non-living. However, the real question is what is lifeis much more complicated. Great minds, from Aristotle to Hesse, offered their explanations, but ... still have not come up with a definition of life that can be applied to everything.
- 1 Scientific definition of life
- 2 Signs of the living
- 3 Life on other planets
- 4 What is the mystery of life?
The scientific definition of life
What is the problem? If in ancient times people really could have approached the issue of life so simply (man is living, stone is not), then with the development of technology this idea has lost its weight. It is used only by people in everyday life. Astronomers, scientists and chemists believe that a much broader concept is hidden under life. NASA aerospace agency describes life in a very interesting way.
A life - A chemical system that supports itself and is capable of Darwinian evolution.
However, this is just one definition of hundreds. Even worse, scientists from different disciplines put forward different ideas about what is needed to define something living. From the point of view of physicists, life is inextricably linked with thermodynamics; chemists believe that this is a set of molecules; biologists are what can evolve.
Signs of living
We were all told biology classes at school.about seven processes that supposedly determine life: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. But this is far from an accurate statement. There are many things that we could push into this framework and call it alive. Some crystals, infectious proteins and viruses will be "living", based on these seven principles.
Really, viruses live or not? From the generally accepted point of view, no, becausethey have no metabolism and they remain inert until they collide with the cells. With all this, viruses possess information encoded in DNA or RNA. It is a powerful marker of life that any living being on the planet has. It suggests that viruses can evolve and multiply. But for this they will have to “crack” the cells and destroy them. Therefore, some microblogging are proponents of the theory of "live viruses."
For many chemists, replication is a process thatviruses can be carried out only with the help of biological cells - it helps to determine life. The fact that informational molecules - DNA and RNA - provide replication, suggests that they are an essential feature of life.
Life requires movement - Aristotle.
Life on other planets
It’s a completely different matter - when people talk about lifeastronauts and scientists who seek life on other planets. The basis of the idea of life they take microorganisms that are able to survive in extreme conditions - for example, tardigrades. These organisms act as "test samples" of extraterrestrial life. That is, scientists believe that alien beings will inherit the key characteristics of life that we know on Earth.
But this approach, as it turned out, contains manyflaws. At the end of the 70s of the last century, the Viking-1 apparatus landed on Mars, which in the course of tests found out that there was life on Mars: the level of carbon dioxide in Martian soil was high, which means that microbes lived and breathed in it. And now carbon dioxide is ubiquitous and is due to the far less exciting phenomenon of non-biological oxidative chemical reactions. That is, the chance to find life this way is no higher than winning the national lottery in the USA.
In 2010, the discovery of bacteria with DNA containingarsenic instead of standard phosphorus, struck many astrobiologists. Although this find has since been called into question more than once, many quietly hope that life on other planets will not follow the classical rules. Now scientists suggest that aliens can be based on silicon, or use other solvents (not water). Or maybe for life they do not need nutrients at all - these are metal machines that can survive in any environment.
The problem is that trying to define lifegreatly complicates the process of searching for other organisms. For example, another NASA rover can pass by a Martian simply because it does not recognize it as a living creature. It will be programmed a certain set of signs of the living, none of which will suit an alien creature.
What is the mystery of life?
So far, the main mystery is to find out what is life. As we saw, often its definition canDo not fit the generally accepted parameters. But we still know one thing for sure: the things that we consider important are actually only characteristic of life on Earth. In the end, everything on the planet, from bacteria to readers in our Telegram chat, came from one common ancestor. But in the Universe, our earthly life can turn out to be only a tiny point among the data.
Although on Earth we did not investigate everything. Get out just recently life was found in one of the most extreme places on the planet.
Until we discovered and explored alternativelife forms, we cannot know what signs, important for our life, are really universal. In other words, we need to find aliens. And until this happens, you can be guided by the logic "man is alive, stone is not." Anyway on Earth.