Life is only believed to be sustainable under a certain and complex set of conditions - basically the proximity of the nearest star to the host planetary structure and the correct blend of elements and conditions and characteristics required to sustain and diversify life.
Although other elements do form a variety of molecular structures, carbon has a unique tendency to form a very wide variety of long molecular chains and rings that form the basis for organic compounds (with hydrogen and oxygen) that at some level of complexity begin to self-replicate. It is speculated that life can evolve without carbon (silicon is the most speculated because it has similar chemical properties to carbon - relatively light with a half full outer electron arrangement, but it can be argued that silicon based molecules are traditionally very brittle). However the overiding argument is probably down to one simple fact - carbon is statistically more abundant than any other element believed to be able to support life in the universe (according to analysis of research samples of interstellar material).
Therefore carbon is the most likely candidate for being the element that life is based upon throughout the universe - but then again the universe is vast and some anomolies will exist there.
Read on for more information from WikiAnswers contributors:
* It's very possible that non-carbon based life could exist. We tend to view science and what we believe is possible from the standpoint of our earth and what we see here. However, we haven't figured it all out yet (which is why scientific explainations for things change) and there may be life in the universe based on elements we haven't discovered yet.
* Everything is accurate except for the first remark, that a certain complex set of conditions is required for life to exist. Life itself is a self-repeating pattern which can hypothetically exist in a universe without chemical systems, and very different properties. Life might exist in the coldness between stars. A complex set of circumstances ise necessary to sustain say mammalian or amphibian life, but that is because those organisms adapted to their environment and therefore need roughly those conditions to survive. Half of the life on earth lives in conditions that would instantly kill the other half. Take a desert animal and put it in the arctic and it will die immediately, and visa versa. Take any land animal and put it at the bottom of the ocean and it will be a) instantly crushed to death, b) drowned to death, c) die of hypothermia or if near a volcanic heat vent boil to death and be poisoned by the toxic gasses it spits up - yet this environment is ideal for organisms which live under that pressure around those heat vents and need them to survive.
Life adapts to it's environment, and life of some sort could potentially exist in any solar system, planet or even universe which had some level of stability and potential for "work" or movement on any scale.
To say life was limited to only carbon based anatomy would be a huge underestimation of life by mankind. First you have to ask what is life. In many definitions fire can be called life. It breathes, eats organic material, and is not based of carbon but of oxygen and its byproduct being CO2. Many people believe for one reason or another that silicon based lifeforms would be a very possible branch of life. However life WAS ,as in past tense, believed to be only present under certain conditions. Reasons such as, needing a large Jupiter to clean out asteroids, or having a near by Ort cloud to hurl comets containing water, hydrogen, nitrogen, and many other precious life giving forces to Earth. However as we learn more about the workings of space we learn new things that kick aside our original theories and concepts. Take the Sun revolving around the Earth for instance.
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Carbon-based life can exist in all kinds of harsh conditions. The question really is whether or not life could have come about through some pathway other than a carbon system. While carbon is by far the most likely candidate for champion of life development, no one can seriously and definitively say that other kinds of life are impossible. If such life exists, it will probably be a very long time before we encounter it.
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Magyarul az a kérdés, egyesek miért hiszik azt, hogy mindent tudunk az életrõl és az univerzumról?