Verschiebung der Kontinente, eine kritische Betrachtung
published: Jan 1, 1955
Results of geological, geodetic and geophysical investigations indicate that at least in several areas surrounding the Pacific Ocean displacements of parts of continents relative to each other at a speed of roughly 1 mile in 100,000 years have occurred during recent geological periods and that such movements still continue. The continents surrounding the Pacific seem to have moved prevailingly towards the Pacific for long periods during the past, but at present motions tangential to the Pacific prevail in many sectors. There is no agreement yet whether or not continental blocks have drifted thousands of kilometers relative to the earth's poles of rotation or similarly relative to the average position of the magnetic poles. Nearly all of those who believe that such large movements have occurred came to the conclusion that the north pole of rotation as well as the magnetic north pole have moved during the past several hundred million years from somewhere in the central Pacific, perhaps roughly 2000 km north of the present equator, to their present position. This could have been the result of a movement of the earth's axis relative to the whole mantle. On the other hand, the viscosity (corresponding to a time of relaxation of roughly 10,000 years) is not too great to permit large blocks with a thickness of roughly 100 km to move relative to the main portion of the earth's mantle as a result of (viscous) flow and thus cause apparent large polar movements. The present structure of the earth's crust could well be a consequence of a drifting apart of continental blocks forming originally a single continental block. In discussions of this and other tectonic problems the possibility must be considered that the MOHOROVICIC discontinuity, which is taken as the lower boundary of the crust, is the result of a phase change. In this case, appreciable changes in the depth of the discontinuity could be produced under favorable circumstances in regions where the temperature of the crust is changing even by a small amount. The history of the earth's crust is much more complicated than it is usually assumed. Many more observations of various kinds are needed before hypotheses concerning the development of the earth's crust can be considered trustworthy.