Why do we assume that extra-terrestrial life requires water or carbon?

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Offline Fluid_thinker

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Why do we look for Carbon based life and water dependent life?

It seems awfully arrogant that we assume that it is the only form of life that would exist.
« Last Edit: 12/03/2009 09:43:40 by chris »


Offline Vern

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Maybe it is just that carbon-based life is the only life form that we know about. I have seen speculation that silicon might be a candidate.


Offline Don_1

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As Vern has said, it is the only form of life we know of, so it is easier to look for something you stand some chance of being able to identify, rather than something you don't know if you will be able to identify as life.

But you are right, we should try to keep an open mind.
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Offline Kryptid

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Polymers with an all-silicon backbone tend to be much more unstable than carbon polymers. Some do exist though, such as polydimethylsilane.

I find it somewhat annoying that silicon-based life is often depicted as being crystalline in appearance. What is that based on? The fact that silicon often takes crystalline form in nature such as quartz? That's hardly a good analogy. Afterall, if we were aliens and we wanted to predict what carbon-based life would look like, would we say that they would be gaseous or liquid because carbon often takes such forms in nature (such as carbon dioxide, methane, and benzene)?

Silicones are much more stable than pure silicon polymers, as they contain oxygen atoms in the backbone. Some are resistant to high temperatures and some are flexible. There are some limitations of silicones relative to carbon polymers. For example, you can have stable double bonds with carbon polymers, but not with silicone backbones. This increases the ability of carbon polymers to form either flexible or rigid structures, whereas silicones are more limited.

Yet other systems besides silicon and silicones might work. Polyphosphazines are composed of phosphorus-nitrogen backbones. These polymers are flexible and make good elastomers.

You might also have a carbon-based life form that uses another solvent to mediate its chemical reactions in place of water. On planets that are cold or have high atmospheric pressure, you might have ammonia, methane, or hydrogen fluoride-drinking aliens. Dimethylsulfoxide might work on temperate worlds.
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Do you think an intelligent designer could cope with more than one form of life chemistry?