EARTH’S FORMATION

Dominion, Volume 28, Issue 92, 12 January 1935, Page 21

EARTH’S FORMATION

Modern Theory Explained By Sir James Jeans

MOVEMENT OF CONTINENTS

Every year for more than a century the Royal Institution has invited a scientist to lecture at Christmas time in a style “adapted to a juvenile auditory.” This does not necessarily signify that the lecturer addresses children: actually his audience usually ranges from infants, of eight to savants of eighty, all of whom he is expected .to interest.

When, as last year, the chosen speaker is an astronomer, no less distinguished than Sir James Jeans, the well-known author of “The Universe Around Us” and “The Mysterious Universe,” his observations are certain to be of sufficient interest to merit preservation in, book form, and this has been done by the Cambridge Press, under the title of “Through Time and Space.” In this work an exceedingly interesting modern theory known as isostasy has been advanced to explain the formation of mountains, islands, continents, and other such large exeresences on the earth’s surface. This new theory asserts, in short, thdt mountains float upon the surface of the earth just as ships float upon the sea. Sir James Jeans explains that this earth, which seems so solid under foot, is actually a plastic lump. much as ordinary pitch is plastic, or ice. Pitch is sufficiently plastic to yield to longcontinued pressure just, as water yields to instant pressure. Pitch will yield in the course of a few hours, or days; ice will yield in the course of months or of years, as the flow of glaciers reveals; glass will yield in the course of decades or centuries. A Liquid Cone. It will serve the purpose of the isostasy theory if'the substance of which the earth is made will yield to tremendous pressure, such as the vast weight of a mountain range must exercise, in the course of millions of years. This is so highly probable as to be almost certain, when it is recalled that seismologists have ascertained the earth’s inner core, some 22,000 miles in radius, to be liquid. Earthquake waves of the type known- as “transverse” do not pass through the central core, and such waves are transmitted by solid matter, but not by gas or liquid. Moreover, just as pitch is more pliable as it becomes hotter, it is probable that the deeper, and consequently hotter, parts of the earth are more pliable. Just as a ship’s height above the sea. is dependent on the weight of water she displaces, so the height of a mountain depends upon its total weight. “The most refined and careful observations of which science is capable indicate that this theory gives an accurate account of the observed heights of mountains,” says Sir James Jeans. The Old and New Worlds. Ho advances also a still more recent theory, that of a German scientist called Wegener, who maintains that not only do the continents and large islands float upon the earth, but they can recede from or approach one another, although, of course, at an incredibly slow speed. The new and old .worlds are supposed by exponents of this belief to have been once united, and to have broken apart, and geologicalsimilarities between the Brazilian coast and the Bay of the Cameroons On the west of Africa are claimed as evidence. The theory of isostasy inaintains also that the general levelling of the hills by wind and weather, a process’which is continually going on at a comparatively rapid rate, is gradually compensated .by the ’ country’s floating higher in proportion as it loses weight, and so regaining height’. This would explain the way large tracts of country, obviously once part of the sea-bottom, are now situated far inland and high above sea-level. False Comparison. . Sir James Jeans points out also, while discussing the irregularity of the earth’s surface, that the oldfashioned comparison of the globe with an orange is wholly false and exaggerated..; a billiard ball would be a far apter simile. In the first place, the earth is commonly thought to be a sphere much flattened at the poles, but this flattening is actually comparatively slight; the longest diameter is only 27 miles longer than- the shortest, a difference of 1 in 3.00. Secondly, the earth has not really a rough skin like an orapge: the highest mountain, Everest, is not 54 miles high, and on a twelve-inch geographical globe the overlap of the paper represents a precipice about seven miles high. Even in an aeroplane, then, we cannot mount very far above the earth’s surface, but we can go quite high enough to see the little hills flattening out. Sir James does not limit himself in these lectures to the earth alone. He speaks also, a_nd with the same vitality, of the sun, the moon, and the sky. As he says, he takes his students on a voyage through space and time until the earth looks less than the tiniest mote in a sunbeam, the, whole of history shrinks to the tick of a clock, man’s life to less than the twinkling of an eye, and the universe appears a vast desolate desert of unthinkable extent and almost utter emptiness, containing only small particles of cold, life.less matter at rare intervals, and still rarer balls of flaming gas, which we call stars.