[Fyron]

Originally posted by Taera:
you're speaking of earth's chemistry and physics. You cannot claim that next solar system's physics arent different and that there are no other kinds of particles/elements there. there is a little too much "cannot" here because humans had not explored much outside the Earth. If realy, how can you know we wont find some unique element even deep in mars, in the asteroid belt or on Pluton?

Because matter is fundamentally ordered. It can not exist in bizarre new combinations, for all stable combinations exist on earth (naturally or in labs). Except, of course, those theorized stable 180 proton elements (anything past 118 or so (or is it 124?) is highly unstable and collapses within fractions of a second when produced in a lab), which are very unlikely to exist anywhere in nature.

Originally posted by Jack Simth:

quote:

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Originally posted by Imperator Fyron:
Complex alien organisms that do not rely on oxygen could not rely on a single gas; they would have to use several things to fulfill all of the roles of oxygen.

And the problem with relying on multiple things is what, exactly?

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The more things that have to be relied on when life is evolving, the less likely it is that it will evolve in that manner. I did not say it was impossible for such a thing to happen, just less likely.

Henk:

If not oxygen but another molecule, that can generate sufficient amounts of energy in biological processes, was used in evolution, then life would have adapted to this situation, and proteins and other processes would have developed that would exploit this resource, making this molecule look "just perfect". Maybe then we would have laughed at the thought of oxygen-dependent life.

Yes, but what molecule would that be? It is all fine and well to make statements like that, but without any examples, it is meaningless.

DS:

By the time you eliminate the ones that can only exist in a proton accelerator/ the centre of a star/ supernova/ black hole etc, you find that there are only about 100 or so elements actually available to Mother Nature for making life. We know the properties of all of those elements, and so we can make some pretty good assumptions about what aliens will be made of.

Exactly.

Oleg:

It is mostly CO2 with some water vapor. N2 is not important for us to breath, Appolo astronauts used pure oxygen. Proved to be very dangerous though - Appolo 1.

I forget exactly how it benefits us, but nitrogen is used by some bacteria that live in our lungs to produce some proteins or somesuch that are vital to us. These substances can of course be ingested artificially.