Intellectual activity both tumultuous and fertile agitated European and North American scientists in the early XX Century. They rediscovered the late XVIII Century works of geologists ahead of their time; they appreciated the ideas of forerunners from Lyell to Hutton and Suess; they came to reconsider from a geological standpoint not only Leonardo da Vinci but Niels Stenon as well. Today’s geologists are aware of the debt they owe to all the many scientists who preceded Alfred Wegener and his continental drift theory. Some have already received just recognition (Snider-Pellegrini, Taylor), at times beyond their merits, while the thinking and work of others still awaits proper placement in the broad intellectual panorama to free them at last from the undeserved bonds of alleged provincialism.
The idea that orogenesis was regulated by basic laws of mathematics and physics was rather widespread at the beginning of the XX Century. For decades then the theory that the shape of the Earth and its deformations originated in accordance with the laws of geometry and based on tetrahedral and octahedral symmetries was universally accepted, having received confirmation at the first meetings of the International Geographical Congress. Congress VII opened in August 1897 in St Petersburg, Russia, under the banner of these ideas, but of others, too. University of Turin geology professor Federico Sacco took as his point of departure considerations then difficult to disagree with, such as the differential torsion by Antonio Praturlon
involving the two hemispheres which was thought to have given rise to the deformations in the Earth’s crust. Further held in great consideration were the astronomical reasons providing an explanation for the planet’s characteristic ellipsoid shape. In view of the fact that the polar depression was just 21,000 metres and that the difference between the maximum elevation of the continents and the maximum depth of the oceans was approximately 18,000 metres, might not there be an identical physical cause underlying the phenomena? Sacco considered three main subdivisions in the Earth’s crust: the ancient massifs, the recent orogenetic areas and the ocean basins (ancient and recent). The ancient massifs have no tectonic activity, and in particular are devoid of vulcanism, which latter is instead concentrated in areas subject to orogenetic waves where fractures and seismic activity are likewise most frequent. The contraction of the Earth and the force of gravity are responsible for the orogenetic pulsations which, however, affect only those long, narrow areas leaning against ancient cratonic masses. As can be seen, these ideas are commonplace today, but back then they must have seemed in the vanguard --at times heretical -- above all due to the mechanism indicated as the cause of the phenomena – the same sort of criticism that in later times would be levelled at Wegener’s force of flight from the poles theory. Federico Sacco reached a surprising conclusion in embryonic form prior to 1895, which he expressed as a formal theory in 1906: if we carefully consider the southern hemisphere – oceanic for the most part – and the northern hemisphere – continental for the most part – we find that the fragments of scattered continents divided today by intermediate oceanic depressions can be theoretically joined together like the pieces of a puzzle to form a perfectly homogeneous super continent. A geographic point of departure such as that adopted by Snider-Pellegrini was not involved, nor the initial staring point of Wegener himself, but rather strictly geological considerations within a sophisticated theoretical framework, although not without ingenuousness and obviously bound to data then available: the great geological structures continuously pursue each other from one continent to the next. Sacco states in particular that, “If we draw together the ancient massifs, excluding the intermediate oceanic depressions,” we thus obtain a pattern of the continental hemisphere wherein the correlations between the massifs are very high. Once again, Sacco: “The impression and the idea that arise spontaneously from an examination of this raised or continental hemisphere is that it really did exist in the beginning and that it subsequently fissured and fractured irregularly so that the different parts (five main ones) detached, spreading out around the central Indo-African core. The result could have been an equal number of continental massifs (Eurasia, Australia, the Antarctic, North America, South America) detached from each other and separated from the great core massif by an Atlantico-Indo-Mediterranean ocean belt”.
Here we are in 1906. Six years later Wegener formulated his first intuitions pertaining to the coastlines of Africa and South America. Nine years later in his famous Die Entstehung der Kontinente und Oceane Wegener expounded continental drift in a revolutionary theory which day by day is being discovered to owe its birth to new fathers.