[henk brouwer]

Originally posted by Imperator Fyron:
The problem is that there are no other substances that can perform all of the roles of oxygen in complex organisms. All organisms on Earth that are more than a simple cell rely on oxygen for all parts of energy generation (not necessarily storage, as for plants, but the molecules they store it in still rely on oxygen). This is because oxygen is a very unique substance that has just the right combination of electronegativity, molecular mass, size, charge, ionization, etc. to work as it does in organisms. 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 yes, they all need to be fulfilled, because they are too fundamental to be ignored (all relating to energy transmission within the organism and releasing the energy to be used).

Earth life is so dependant on oxygen that some scientists say, as Fyron mentions, that oxygen is the only substance with just the right characteristics for (complex) life. The question is whether this is realy the case or caused by the fact that life has adapted during millions of years of evolution in such a way that it perfectly exploits the characteristics of oxygen, which may make it seem perfect.

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.

[ July 16, 2003, 11:33: Message edited by: henk brouwer ]