Not hard for me to imagine. I’ve always believed that life is varied in the universe. Varied, but abundant. Too many chances for life to spring up. The kind of life we would recognize and I’m sure scores that we wouldn’t know were living things.

Unlikely. Complexity requires a lot of energy. Over a long period of time. So helium is not helpful. Unless our sentient ET is a big star with a brain.

@mattbrowne Complexity requires a lot of energy. As we know it, but some other entity on some other planet might trive off an atmosphere of xenon, neon, methane, etc. Because our lungs work best in high oxygen doesn’t mean another being on some other planet has to. ;-)

@Hypocrisy_Central – Most astrobiologists have a lot of doubt about this hypothesis. The studies of terrestrial extremophile species give us a lot of clues why this is so. Xenon and neon can’t be a source of energy. Anaerobic organisms do not depend on oxygen, though. But the question is about sentient beings, not primitive extremophiles. See

http://en.wikipedia.org/wiki/Astrobiology

I have always thought this myself. Just because life on this planet needs certain things survive doesn’t necessarily mean that life on another planet does and they may thrive off things that we have no use for.

However, I respect the fact that @mattbrowne is far more qualified than I am to answer questions like this.

No; it isn’t a stretch for me to imagine! lol I think of them as humanoids.

@mattbrowne OK, but the main question still exist, the theory and ideal behind these extremophile species is based off Earth, how they survive or maybe thrive here under the conditions that exist here. We don’t really have a template out there to use because we have never gotten out there. It would be as if we flew over a jungle but could never reach it by foot to explore we could only imagine what was there by where we have been. Some of what is there might be totally different from what we could have imagined. Because here on Earth harsh conditions like thermo vents, etc. could only sustain extremophile species, somewhere out there maybe these primative species could be the ones depended on oxygen and the main species depended on something that here would bo considered harsh.

@Hypocrisy_Central – I think the debate is about what “totally different” can mean. Star Trek was very creative and there were even intelligent floating white nebula. Most astrobiologists today reject these forms of life and even point out totally different could still mean not so different from the extremophile species we know. Why is this so? Well, first of all astronomers now have a pretty good idea about the abundance of elements in the universe and our galaxy. They also know which complex molecules exist in space. Chemists have a pretty good idea about exothermic and endothermic chemical reactions and these reactions pose certain limits. Even totally different life cannot use helium or neon. As for energy sources in general there are only three options: sunlight, residual heat of forming planets and radioactive decay on planets. A stable energy source is required for complexity to evolve (because of the second law of thermodynamics) and therefore there’s some limit how harsh an environment can be. Astrobiologists think it can’t be extremely harsher than Earth’s harsh conditions. Plus any extrasolar planet hosting life needs protection from x-rays and gamma rays and other forms of cosmic radiation because they destroy complex molecules.

But the issue is controversial, no doubt. Here are some interesting links

http://www.daviddarling.info/encyclopedia/E/evoltheo.html

http://www.daviddarling.info/encyclopedia/E/etlifevar.html

http://www.daviddarling.info/encyclopedia/E/etintelchar.html

http://www.daviddarling.info/encyclopedia/A/alternative_forms_of_life.html

“There was also, and continues to be, disagreement over how different extraterrestrial life is likely to be from the varieties found on Earth (see extraterrestrial life, variety). Again, the dispute centers on the relative importance attributed to factors of chance and “contingency” on the one hand, and necessity and determinism on the other. How far up the ladder of life do significant differences begin to appear between the life-forms that have evolved on one world and those that have evolved elsewhere? The commonality in space of basic organic chemicals such as amino acids suggests that they and the larger units into which they polymerize, including proteins, may be general ingredients of life throughout the Universe. The phenomenon of convergence also argues in favor of cosmic similarities between life-forms. Set against this, however, is the vast morphological diversity of organisms on Earth and the major, unpredictable effects that random cosmic events such as asteroid impacts can have on the course of evolution (see cosmic collisions, biological effects). These factors suggest that, over all of space and time, life must be almost unimaginably diverse.”