LIFE ELSEWHERE IN THE UNIVERSE ?
(Extracted from e-mail correspondence with friends):
We can do no more than speculate about possible contacts with alien life, although we can nevertheless bring a certain amount of logic into a discussion of that nature, for example by citing analogies with events and circumstances here on Earth.
Various alternative scenarios can be suggested. The aliens could well be so far ahead of us, technologically and otherwise, that they would completely dominate our planet, and we would be eliminated - or at best marginalized; that might be comparable with the fate suffered by the Tasmanian and Australian aboriginals, who effectively lost their continent to European invaders.
Or perhaps the aliens will have the advantage of superior technology but we might still be capable of learning at least something from them, such that we would perhaps be able to adapt and try to come to terms with the new situation; that could be similar to what happened in Africa during the first half of the 20th century?
Or maybe the aliens will find that conditions here do not suit their own metabolisms - e.g., the proportion of oxygen and the air pressure in our atmosphere might be markedly different from what they are used to breathing (assuming of course that they derive their energy from oxygen), or our gravity might be significantly higher than what they are comfortable with ... never mind all the viruses and bacteria which we have floating around > (remember how the Mexican Indians died like flies when exposed to ordinary European diseases? - except that aliens could obviously bring their viruses with them - but there is a good chance that our viruses will be more of a threat because our standards of hygiene could well be lower than theirs?) ... Anyway, just as tropical West Africa was not particularly hospitable for European settlement, we can perhaps hope that incoming aliens will find Earth even less suitable ... unless they can get round the problem by building and sending down robots!
Regarding differences in atmosphere, incidentally, if we were to stumble upon a planet which was similar to what ours was like several hundred million years ago - then we might well find it difficult to stay alive in its atmosphere - even if we managed to keep all the dinosaurs at bay! (But can you imagine the smell ?) ... Before the Angiosperms (flowering plants) appeared on the scene, did our atmosphere contain less oxygen and more carbon dioxide than it does now?
(A few brief notes which helped to answer questions following a talk):
There might just be microbes on Mars - but not insects or animals. Or perhaps there used to be microbes and bacteria there - when there was water.
Jupiter's moon Europa is another possibility for very primitive life; there may be water there too - not on the surface, but deep underground where temperatures are high enough. Saturn's moon Titan is also intriguing - but any life-forms there would need to use ethane as its carrier-liquid, instead of water.
Establishing bases on Mars should be feasible within a few decades. Oxygen could be extracted from (the very oxygen-rich) compounds in the soil. There is water in the Martian ice-caps.
If we are prepared to look millions of light-years away, then eventually we would probably find a star system and planets similar to ours, with advanced life. Alien monsters cannot be ruled out, but life-forms need to be reasonably efficient in order to thrive. For example, a head (with brain) which is fairly high above the ground is safer from attack than one which is low down. Eyes, ears and even the nose and mouth should preferably not be too far from the brain, because long lines of communication (through the nerve-fibres) would mean that failure or malfunction would become more likely (for example through amputation). Too many limbs would probably be clumsy; (admittedly insects have six; the octopus is not really among the highest forms of life).
So I would not be surprised to find creatures elsewhere in the universe which look almost human. Also, warm-blooded organisms like mammals tend to be more vigorous and more versatile than cold-blooded ones like reptiles.
We will probably need to go an enormous distance away to find intelligent life, because our equitable climate and ecosystem seem so heavily dependent on favourable physical properties of our Earth and Solar System - which could easily have turned out differently. Several critical factors would make all the difference between a hospitable star system - and one where higher life-forms might find it difficult to develop.
We just happen to be lucky:
(ii) with the presence of quite a large Moon - which stabilises our angle of spin. In contrast, Mars's spin axis has fluctuated quite markedly during the last few million years. In addition, the large tidal range produced by our Moon could well be important.
(iii) with the existence of a large Jupiter to sweep up most of the stray comets and asteroids. (However, it is interesting that we did need just one rogue asteroid 65 million years ago - to remove the dinosaurs and make way for the rise of the mammals).
(iv) with the almost circular planetary orbits in the Solar System. These are therefore more likely to remain stable for thousands of millions of years. Earth's near-circular orbit also means that our summer to winter temperature-change is not as great as it would otherwise be.
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