INTERPLANETARY EQUILIBRIUM: Throughout the history of civilized man people have often posed the question 'Why is there life on earth?' and endeavoured to answer it in a variety of ways, some religious, others scientific. The different viewpoints appertaining to the reasons for life on this planet, and man's relationship to whichever of the heavenly bodies he has hitherto been aware of, have ensured that, with each succeeding generation, the question is posed and answered in a different way or, at any rate, in a manner considered most suitable to the understanding of the people of the time.
At present it is the scientific viewpoint which prevails over the religious one where the interpretation of this perennial mystery is concerned, and so it is to science, in its manifold guises, that a majority of people look for a solution to those problems which have vexed the greatest minds of the past. True, unlike religion, science does not and cannot lay claim to omniscience in these matters. But with its largely empirical if not hypothetical basis, it does at least suffice to draw one's attention to possibilities which religion, grounded on a 'rock of faith', would categorically deny, and thus facilitate the way for further and more detailed inquiry. And so the question 'Why is there life on earth?', considered scientifically, demands an answer that will appeal to the contemporary mind in terms it will understand rather than in any previous or outdated terms. Admittedly, I am not a scientist. But, as a philosophical writer, I can at least draw conclusions and formulate hypotheses roughly compatible with a scientific outlook. Hence the most obvious answer to the difficult question we have posed is: 'Simply because life on earth was made possible.'
Of the major planets currently known to man in the Solar System, it is a general assumption that the earth is the only one with any form of intelligent life and, in all probability, any life at all. We no longer believe in Martians or the possibility of autonomous life on Mars, and with our growing interest in the more distant planets we are fast coming to the conclusion that life of whatever kind would be even less likely to exist on them. And so if the earth is the only life-sustaining planet, it may well puzzle some people what the other planets are for, why, in fact, they exist at all.
My own theory of this is, I think, a fairly plausible one - plausible, that is, for those who suffer from a need to justify the prevailing cosmic order-of-things in this part of the Galaxy. Whether or not the other planets exist primarily to serve the earth, it seems that their existence, willy-nilly, guarantees the life-sustaining power of the earth simply by keeping it in a position, relative to themselves, where life is made possible, but where the absence of one or more planets from the prevailing order of things would so alter its orbital distance from the sun as to render life on it utterly impossible or, at the very least, extremely improbable. Therefore we must assume that there exists an interplanetary equilibrium which renders no planet superfluous, but keeps them interdependent in the interests of a given planetary system. Life is made possible on the earth because its distance from the sun - in part established by the gravitational pull of each individual planet - gives rise to the formation of a life-sustaining atmosphere, an atmosphere which could not exist on any planet positioned either closer to or farther away from the sun. Thus life could only be made impossible on the earth by something which destroyed the prevailing interplanetary equilibrium, removing one or more of the planets and thereby necessitating the establishment of a different equilibrium - one which would so alter the earth's position vis-à-vis the sun as possibly to transform it into the rough equivalent of Venus or Mars.
Now if, in consequence of the destruction of Mercury, Venus was 'pulled in' to a much closer position to the sun, it is highly probable that the earth would also be 'pulled in' to a much closer position to it, and that Mars, which would also be drawn-in closer to the sun, might duly find itself in a position where life was made possible there in consequence of the formation, over a long period of time, of a different atmosphere from what it now possesses. Thus Mars would become the rough equivalent of the earth and, willy-nilly, the earth the rough equivalent of Venus, where the maximum surface temperature is believed to be somewhere in excess of 800°F, which is to say about 3¾ times that of boiling point. However, the difference of mass, volume, density, etc., between the various planets would undoubtedly affect their relative positions in the Solar System if such a change were to occur, so we cannot be certain that Mars would necessarily take up a position exactly corresponding to the one currently held by the earth. But an approximation there could well be, and if this approximation of Mars to the earth was such that the formation of a life-sustaining atmosphere became possible, then there would almost certainly be life-forms on Mars after a number of millennia.
But in returning from such 'far out' speculation to the Solar System as it now stands, we cannot be sure to what extent the prevailing interplanetary equilibrium is governed by the sun and to what extent it is also governed by the nearest foreign stars in the Galaxy (as indeed the Galaxy and perhaps even the Universe as a whole). It is, at any rate, unlikely that the Solar System is a self-contained and totally-isolated unit which exists independently of the rest of the Galaxy, of which the sun is but a comparatively minor star. My own theory is that the equilibrium of the Solar System is predominantly governed by the sun but not exclusively so. Likewise, if the core of this planet is molten hot and becomes progressively cooler and harder towards the surface, my own theory as to the mechanism underlining this equilibrium is that there are other planets that also possess a molten core which exists, like the earth's, in an antithetically magnetic relationship to the sun, but which is prevented from being sucked-in to it by the magnetic influences being gravitated by certain other stars in the Galaxy which to a certain extent counteract the sun's magnetic influence and thus produce the tension necessary to maintaining the orbital variations of the individual planets. Of course, I have to admit that all this is purely speculative. For as far as a comprehensive knowledge of the Galaxy and the workings thereof are concerned, we are still in our infancy, not even having acquired a comprehensive knowledge of the Solar System!
However, as to the question 'Why is there life on earth?', I think the fact of its position vis-à-vis the sun must be taken as the most credible answer, so that our attitude towards the other planets should encompass an awareness of their function as a means, effectively, to keeping a life-sustaining atmosphere in existence.