You can Often find messages like "astronomers believe that the planet xxx could be a life" or "to find life, you first need to detect signs of the presence of water" and so on. But what do they mean by "life"? All that only knows how to breathe? Or eat? Or it should move? We don't think about it, when we are asked to distinguish the living from the dead: the man — alive, the cat — live, the closet or the car — dead. In fact, however, the question of what is life is much more complex. Great minds, from Aristotle to Hesse, offered his explanation, but... still not come up with the definition of life, which can be applied to all.
What is the problem? If in ancient times people really could just walk up to the question of life (human — living stone — no), then with the advancement of technology, this idea lost its weight. It's only used by people in everyday life. The same astronomers, scientists and chemists think that the life is much more broad concept. Very interestingly describes the life of the space Agency NASA.
However, this is only one definition among hundreds. What's worse, scientists from different disciplines have put forward different ideas about what you need to define something that is living. From the point of view of physicists, the life is inextricably linked with the thermodynamics; chemists believe that this set of molecules; biologists — something that can evolve.
All of us at school in biology lessons were told about the seven processes that supposedly define life: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. But this is not an accurate statement. There are many things that we could cram into this framework and be called alive. Some crystals, proteins and infectious viruses to be "alive", based on these seven principles.
Some believe viruses are alive, because they have the information encoded in DNA or RNA
Indeed, viruses are living or not? From the standard point of view — no, because they have no metabolism and they remain inert until then, until you face the cells. With all this viruses have the information encoded in DNA or RNA. It is a strong marker of life that is available to every living creature on the planet. He suggests that viruses can evolve and multiply. But for this they will have to "hack" cells and destroy them. Therefore, microblogging, some are supporters of the theory of "live viruses".
For many chemists replication — the process that viruses can only be carried out by using biological cells — helps to determine life. The fact that information molecules — DNA and RNA — provide replication, suggests that they are an essential feature of life.
Life requires movement — Aristotle.
It is Quite another thing — when the life of the astronauts and scientists involved . Based on the idea of life they take out microorganisms that can survive in extreme conditions — . These organisms act as "test samples" of extraterrestrial life. That is, scientists believe that alien beings will inherit key characteristics of life we know on Earth.
Tardigrades can survive the fall of an asteroid and supernova explosion
But this approach turned out to contain many flaws. In the late 70-ies of the last century on Mars , which tests have found that on Mars was life: the level of carbon dioxide in the Martian soil was high, and so it lived and breathed the germs. Now carbon dioxide is found everywhere and is explained by the much less fascinating phenomenon of oxidative abiotic chemical reactions. There is a chance to find this way of life is not higher than winning the national lottery in the United States.
In 2010, the discovery of bacteria with DNA containing arsenic, instead of phosphorus, was responsible for many astrobiologists. Although this finding since no time questioned, a quiet hope that doesn't follow the classic rules. Now scientists assume that aliens might be silicon-based, or use other solvents (not water). And maybe for life, they do not need nutrients are machines made of metal that can survive in any environment.
something like there is a fence Martian soil
Yet the real mystery is to know what is life. As we have seen, it often happens that its definition may not be suitable for conventional parameters. But one thing we know for sure: the things we consider important, in fact pertain only to the life on Earth. In the end, everyone on the planet, from bacteria to readers , descended from one common ancestor. But in the Universe our life on earth may be only a tiny dot amongdata.
While we have not found and have not studied alternative forms of life, we can't know what the warning signs are important to our lives really is universal. In other words, we need to find aliens. But until that happens, you can follow the logic of "people — living stone — no". At least on Earth.
the more we learn, the harder it becomes to answer this question
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