RHYTHMS OF THE EARTH

Dominion, Volume 18, Issue 191, 8 May 1924, Page 7

RHYTHMS OF THE EARTH

4 CHANGING SEA DEPTHS There is reason to believe that the earth undergoes a recurring series of slow pulsations, changing its contour from age to ago. Unless some wiknown cause of acceleration is at work, the friction of the tides must have the effect of slowing down the earth’s rotation on its axis at a rate which, although extremely slow, has had significance in tho long stretches of geological time and has produced changes iof contour. Nearly ten years ago, Professor A. E. H. Love worked out the theory of the clituijxo in the rate of rotatzioii its influence on the earth’s contour. His results are now being applied towards explanations of tho recurring changes of climate in. the. geological past, evidences of which is. found in the relics of extensive glaciation at many times in the past history of the globe and of the former presence of abundant vegetation in regions which could not at present support more than the scantiest and simplest forms of life. , We know that even the solid part of the globe is not rigid, and the great oceans cover a large part of its surface. If a sphere of plastic but coherent matte- be spun rapidly on its axis, centrifugal force will cause it to become oblate —that is to say, flatter at the poles than round the equator. The amount of deformation will vary with the speed,of rotation and the physical properties of the rotating mass. These changes take place in the case of the earth, but the effects are different on the mooile oceans, and the less plastic solid porProfessor Love asked us 1° , I ' ra l n .cj n * a particular moment at which the lithosphere (tho solid part of the earth) had reached equilibrium with the speed of rotation and had in consequence acquired a definite configuration. Clearly the more mobile oceans, if not in equilibrium at the same moment, would rapidly attain a distribution suitable to the centrifugal forces actmg on them. Land and water, seas, continents, and islands, would thus become arranged according to a plan which was the result of the previous, corrugation of the earth and the centrifugal forces now at work. But the rotation is slowing down gradually because of tidal friction. The surface of the ocean would rapidly conform with a less dilate condition, the tendency to heap up tho water in equatorial zone diminishing. The lithosphere will also change in the same fashion, but much less quickly because of its much higher coherence. The result of this differential action will be that as the land areas are losing their equatorial bulge less quickly than the oceans, the seas will become more shallow towards tie equator and the water will seek the P °But, although the lithosphere offers resistance to change of shape, the stresses produced, will ultimately increase bevond the breaking point. Local fractures will take place, and will continue until there ,is again an approach to a conformation in. i>io general trend of the change will be towards reduction of the equator.:! I bulge. In other words, by relatively sudden and spasmodic movements the equatorial seas will again deepen and the Polar seas decrease. The rhythm of the e rth. due to the secular slowing down of rotation, will thus consist periods of relative quiescence with a tendency for accumulation of water towards the poles, alternating with shorter periods of marked activity during which the water will tend to accumulate in the equatorial belt. If the lithosphere had a uniform suifaee, and if no other factors wete nt work, the rhythm would consist of alterations of Polar continents and equatorial seas with Polar seas and equatorial land masses. —“Tinies.”