What is life? Trying to answer this question often gets people into a dead end. Deadlock begins with the fact that in any language there are lots of definitions of the word “life.” Here, for example, using three different meanings.

Is there life on Mars?
Is there life in this body?
Is life worth to live?

The definition of “life” in three of these cases is fundamentally different. In the first case, life is a collective phenomenon, the second refers to the ability of an individual organism to metabolize and growth, and the third refers to the activity of life experienced by the body over a lifetime. The first two tend to have direct relevance to astrobiology.

The usual definition of life, used in the first case, means a system of material objects that can evolve, reproduced, mutate and were selected. That’s what we’re looking for on Mars and other worlds. It would be interesting if such a life was independent of our origin. It is often noted that the definition of life as a system capable of evolving, suggests that some isolated individuals do not represent a “life.” It is nonsense that confuses the first and second examples of life.

Many experts are of the opinion that an effective search for life on other worlds requires that we must agree on what to call life. However, many agree that if we once understand life, we can make a fully mechanistic and predictable theory of life. For example, take the same water. Water is generally determined by two hydrogen atoms and one oxygen atom. But life – this is not a simple substance like water, but rather a process like fire. The flame has no simple definition. If life is like a fire, even having a purely mechanistic and predicted by theory, we can not define a simple closed form of fire. Search for life on other planets may be based on what makes life, not its definition. For example, it can build large specialized molecules like DNA and proteins.

Крис Маккой

Dr. Chris McCoy

“Viking” whose sole mission search for life on other worlds, focused on the second example. Biologists “Viking” looking for something to live in the sample. It is assumed that if anything lives, it consumes organics and gases; has a metabolism. Thus, the working definition of “life” experiments “Viking” is based on the ability to metabolize under experimental conditions.

But this definition, there are a number of problems. First of all, there are many non-biological processes in which organic matter is consumed and excreted gases. Secondly, our earthly experience has shown that many microorganisms are picky eaters and do not grow in laboratory conditions on food additives. Perhaps the most serious problem approach “Viking” is that it can not detect dead organisms, which, unfortunately, are most likely in a state of Mars, Europe or Enceladus. Search for life in our solar system all have to start with the definition of death.

What does it mean to be dead? This means that once living organism and consists of organic molecules that are specific for life – DNA ATF proteins. It biomarkers that could be convincing evidence that the organism was once alive and is the product of a system of life, which took an evolutionary path. The search for such biomarkers formed the basis of methods to search for life, which are being developed now. The challenge is to develop tools that can search biomarkers Earth-like life, and can also identify biomarkers unknown extraterrestrial life.


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