Science. Lunar Lessons.

Waikato Times, Volume XXII, Issue 1809, 9 February 1884, Page 2 (Supplement)

Science. Lunar Lessons.

I>y Bicnutn A. Pkoctor. This more the moon i 3 studied, the clearer seems to be the evidence that she gives respecting the life history of a planet. Sho tells us more, perhaps, of the future of our earth than of the past; but she tells us of the pant too. That the moon is waterless and practically airless too, now, is certain, and, therefore, there is probably no life now on her surface, though for those who like such fancies the belief h always open that there may be creatures on the moon utterly unlike any with which we arc acquainted on earth. Yet the moon's face tella us of a remote youth — a time of fiery activity, when volcanic action even more effective (though not probably more energetic) than any which ha 3 ever taken place on this globa, upheaved the moon's Crust. But so soon as we consider carefully the features of her surface we see that there must have been three well marked eras of vulcanian activity. Look at the multitudinous craters, for example, around the Metropolitan Crater (as Webb has happily named it) Tycho. They tell U 3 of century after century of volcanic disturbance— but they tell us more. They mark a surface which varies in texture, and therefore in light-reflecting power in such a way as to show that the variations were produced long before the volcanic action began by which the craters were formal. For the variations of texture arc such as to mark a series of streaks — some of them two or three thousand miles in length, and many miles in breadth, extending radially fromTyoho. Craters lie indifferently on these brighter streaks and on the intervening darker spaces, and some craters can be seen which lie right across a bright streak with parts of their ring on the darker regions on both sides of the streak. Of course, this proves that the crater? were formed long after the great streaks. When the streaked surface wa3 formed, it must have been tolerably smooth ; for tho streaks best under a full illumination, and there is no sign of any difforenco of elevation between them and the darker ground all around; they are neither long ridegs nor long valleys, bur mere surface markings. Yet must ihey have been formed by mighty vuloanian disturbance, such, indeed, as we may he certain went on at the early stage of the moon's history, to which these radiating streaks must be referred. It scorns clear that, as Nasmith has illustrated by experiment, they belong to that stage of the moon's history when her still hot and plastic crust parted with its heat more rapidly than the nucleus of the planet, and so, contracting more quickly, was rent by the resistance of the internal matter, which, still hot and molten, flowed into the rents, and spreading formed the long broad atreaks of brighter surface. It seem 3 as clear that the next Btage of the moon's history (after many thousands, perhaps millions, of years had passed) was one in which the cooled cruat, atill plastic, contracted little, while the still hot nucleus contracted steadily, so shrinking from the crust, which, under the action of gravity, closed in upon the nucleus in such sort as to form a wrinkled or corrugated surface. This was the second era of lunar vulcanian disturbance. Tho third was the era of great volcanic eruptions, dv ing which the mighty craters were formed which are so numerous on the lighter tinted higher regions of the moon's surface. Were there no seas or oceans on the moon at this time ? It is strange if there were none, when we consider the connection which exists on the earth between the activity of the great volcanic vents and the proximity of water. It is stranger still if we consider that those regions where, if water had ever existed on the moon, it would have formed seas, are without exception characterised by a different tint, and a different surface contour, from what we find in the regions which would in that case have formed the lunar continents. All the lower levels are dark, are much more uniform, and are maked by few cratera, and those small. This is no mere accident or coincidence. It is a feature which we are justified in regarding as characteristic ; and, so regarded, it seems to force upon us the conclusion that those lower levels are in reality old sea-floors, formed in a different way from the higher levels, and therefore presenting a different tint and reflecting a different amount of light. When we thus recognise in the moon the three stages of past vulcanian energy which Mallet and Dana have recognised (though the evidence has not been quite so obvious) on the earth, and the signs also of a past fitness for the support of life, seeing that the presence of seaa implies also the presence of an atmosphere dense enough to make the boiling-point of water not too low, we tecognise the significance of the evidence which the moon gives respecting the earth's future. What has happened to her will happen also to our earth, though doubtless with variations in details corresponding to different conditions. Yet ssience has good reason for regarding as exceedingly remote the time when the earth will be at the stage of planetary development which the moon has reached. If the earth's crust, God's work, whose teachings, therefore, if we can but read them aright, are God's words, speaks truly, it is certain that tens of millions of years have passed since even that stage of the earth's life through which she is now passing began. But suppose, for the sake of argument, wo put twelve million years only as the time which has elapsed since the earth and moon were at the same (necessarily much carliei) stage of planetary life. The earth's mass exceech the moon's 81 times, ami therefore at that time she had 81 times as much heat to part with as the moon. But her surface is now (and the proportion cannot have been very different then) only some 13 J times greater than the moon's. Thus, since 81 contains 13 J six timea, the earth has parted with her heat at only one-sixth of the rate which would have made the supply last just as long as the moon's. Each stage of the earth's cooling, or of the earth's life, has been six times as long as the corresponding stage of the moon's, and the 12 million years of earth history oorrespaud to about two million years of moon life. Ten million years ago, then, the moon was in the s&me stage of planetary life that the earth is now passing through. But those ten millions of years of moon-life correspond to sixty millions of years of earth-life. Wheref ore, on the very moderate assumption I have made as to the time which has elapsed since earth and moon were both youn^, sixty millions of yeara would have to elapse before the earth would have reached the stage of life through which the moon is now passing. — NeiocastU Weekly Chronicle.

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