Although the theory of continental drift has been widely discussed and accepted, serious doubts have been raised about the period during which the forces causing the drift had operated and also about the direction and amount of force. Some of the objections are also as follows:
1. The fit suggested is hardly perfect and cannot be expected to be real since erosion along the coast lines through long geological ages must have modified them considerably.
2. Fossil plants could have been spread from one continent to another by winds or ocean currents. Similarity of fossils occurring in more than one continent need not signify that the continents were all joined as one, sometimes in the past.
3. Some authorities on geo-tectonics feel it mechanically impossible for such large scale drifting of the continents.
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4. R.T. Chamberlin has pointed out that the petiographic analysis of the rocks on either side of the Atlantic shows that their resemblance is only superficial.
Bailey Willis (1928) has pointed out that the forces which were great enough to have built the Andes-mountains, would almost certainly have deformed South America to such an extent that any similarity of its eastern coastlines facing Africa would have been destroyed and the drifting is quite unlikely.
6. Polar-wandering might have been caused by moving poles rather than by moving continents.
7. The mechanism suggested by Wegener for the displacement of continental blocks did not withstand criticism. According to him, tidal forces due to lunar-solar attraction and the forces of the earth’s rotation were responsible for the drifting of the continents.
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But it was difficult for geologists to conceive of a driving force that could move continents. Sir Harold Jeffreys demonstrated that the forces suggested by Wegener to have caused the drift were either ineffective or inadequate for such movements.
In 1937, Wegener’s views were developed by the South African geologist Alexander Du Toit in his publication Our Wandering Continents’.
Taking into account new palaeoclimatic and palaeontological data, Du Toit advocated that instead of a single Pangea, there had been two major continental masses originally-Laurasia in the northern hemisphere and Gondwanaland in the south-separated by an oceanic area called Tethys\ a sort of proto-Mediterranean. The Alpine-Himalayan mountain chain developed in the place of Tethys by the convergence of the two continental masses.
To explain the horizontal displacement of continental masses Du Toit proposed a different mechanism. According to him, the splitting of the marginal sectors of Gondwanaland was associated with epeirogen- etic oscilations of the crust during the sinking and formation of geosynclines.
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The drifting of the broken-off blocks was associated with an injection of magma and opening of continental blocks. But this mechanism, however, has no quantitative basis and was overwhelmingly opposed
Inspite of vehement opposition from a great number of authorities, the concept of ‘Continental drift* was kept alive with enormous efforts in the 1940s and early 1950s, by Arthur Holmes in England, L.C. King in South Africa, S. Warren Carey in Tasmania, etc.
With the advent of new palaeo-magnetic studies, sufficient interests were regenerated about continental-drift and this set the stage for modem concepts like ocean-floor spreading and plate-tectonics which began to emerge in 1960, which lend support to the theory of Continental-drift.