EARTH ON THE MOVE

Wairarapa Times-Age, 17 October 1938, Page 3

EARTH ON THE MOVE

< 60,000 EARTHQUAKES EVERY YEAR COLLAPSES BELOW THE CRUST LONDON’S RECENT TREMOR London’s recent “earthquake” awak-' ened Londoners who felt it, and others convinced of it against their will, to the realisation that the earth is always on the move, writes E. S. Grew, in the London “Observer.” Few of the 60,000 shivers passing over its skin every year come our way. But the crust below our feet is no more immune from collapse in the long run than that of any other Empire. The underground arches which support the crust never sleep. Their restlessness is easily accounted for by the geologists. Even after thousands of millions of years of spinning the earth has not come to terms with the frozen liquid core of its interier or the imperfectly compacted shells of rock enclosing it.

This scarcely needs explanation. But what is still doubtful is whether the collapses below the crust, and the shrinkage and heapings at its surface, are wholly due to the shifting weights of its land masses.

It is admited that the continents are not the same in shape or size as they were when, many millions of years ago, the earth began to settle down to a domestic life. Even the Age of Reptiles looked on a differently shaped and ordered world.

But in a general way the changes are laid to the work of the wind and the rain. The rivers carry away the dust of ages from continent to ocean, where the sea bed grows heavier while the land becomes lighter. The scale plans rise or fall. The continents sink, the ocean bed rises. Even today we may see the North American continent taking a tilt in the west. In the opinion of Dr Harold Jeffreys, the leading authority on the architecture of the earth, this up and down motion of the continents is enough to account for all the changes of the face of the earth; for the deserts that once, were seas, for mountain ranges uplifted from the ocean bed, for the Himalayan chains crumpled into folds by the creep of Asia, the most constant of the land masses in a changing world. Round and about it the oceans ebbed and flowed through geologic time, producing periods of unending rain, and the Ice Ages. It has been surmised that we now live amid the lingering traces of the last of these. The four or five Ice Ages in the earth’s history, and the changes of climate that have stationed icecaps where tropic jungle was before, are among the chief problems of the structural geologist. . Sir George Sijnpson, our official meteorologist, follows Dr Jeffreys in funding their explanation in the inconstancy of oceans which flood land masses and displace the ice of the poles. . Nevertheless, there is another explantation which, after being roundly condemned, has been revived—Wegener’s hypothesis of drifting continents. Mr A. L. du Toit has lately summed up again the Ayes and Noes of the idea that continents may move sideways as well as up and down. Briefly, Wegener and his followers declare that on a pulsating, restless earth all parts are in movement in respect of the axis of rotation, and always have • been. In the oldest Palaeozoic age which can be traced there were two parent masses, Gonawana in th.e eastern and Laurentia in the western hemisphere. The spin of the earth did not leave these masses merely moving UP and down, like soldiers on parade, but impelled fragments to move radially away from them by tangential forces. In a way roughly analogous, the winds and ocean currents take deflnite paths about the earth’s rocky sphere. Against this idea we must at once put the formidable objection of Dr Jeffreys that we have no evidence that the continents do drift, and none that there is a sufficient force existing to make them. - Such movement is opposed by the rigid tenacity of the crust, which is strong enough to ’ hold up Mount Everest, or to hold down the Tuscarora Deep on the ocean bottom. Can we suppose that a very small tangential force supplied by the earth’s rotation would push these foundations from their bases, hoWever long it acted, and, if so, would it have deposited them in the places they now occupy?

Having stated the objections, we may none the less permit ourselves to admire the elegance with which Wegener’s wandering continents contribute responses to many unanswered questions of the earth’s history and about the life, on it. . They afford a ready explanation ol mountain building by the supposition that a continental block in its travel, after being detached from the parent mass, would develop folds along its leading edge if unopposed; and if one of such travelling land masses came into contact with a second there would be mutual folding along the line of impact. , . „ Secondly, the differential creeping would alter the position of the land masses with regard to the Poles, and sweeping changes of. climate must follow. This is a simple explanation, if not the right one, of the Ice Ages. No

one, whether a Wegenerite or not, can maintain that former jungles, in the Arctic and ice caps in Africa arose from other causes than alterations in the distribution of continents and seas. Lastly, a fascinating feature of Wegener’s hypothesis is that it enables fragments of continents now wide apart to be fitted into one another as in a jig-saw puzzle. A glance at the map of the world between South America and Africa, for example will show what is meant. Incidentally, the supposed joining of these masses would give a plausible reason for the existence of identical forms of life in regions now widely separated by the unplumbed salt estranging sea. There would be no reason to invent land bridges to explain the migration of dinosaurs from the Gobi Desert to the valleys of Wyoming in the Age of Reptiles, or the trek of elephants from African forests to the swamps of the Thames Valley in the Age of Mammals. In other words, all would be simplified in a straightforward world if we could find a tangential pressure derived from the earth spin sufficient to start the continents on their journey and to keep them on the move today.