Continental drift theory
Continent drift: from when, how and until when will the clods dance?
We arrived at 500 million years ago, covering 4 billion years in one fell swoop, it took to build the substratum bearing the earth's crust, characterized by a complex of mainly metamorphic formations crossed or interspersed with eruptive rocks, testifying to the intense tectonic movements suffered by the sediments deposited during that long period.
The intense tectonization of the soils, both due to thermal and dynamic metamorphism, does not allow, on the basis of the lithological characteristics alone and in the absence of indicative traces of fossils, a correlation of the Pre-Paleozoic formations emerging at distances of thousands of kilometers
Despite the limitations indicated above, the study of the most ancient formations of the earth has led geologists to ascertain fundamental events for a paleogeographic reconstruction of the globe, in particular:
- the presence of repeated moraine deposits demonstrates that the hypothesis that for the first billions of years the planet Earth was affected by higher temperatures than the current ones is not sustainable, but that vice versa on several occasions large areas of the globe were affected by glacialisms, especially in Australia, India and southern Africa;
- the whole of the currently extremely rigid lithoid complex, after having undergone several orogenetic cycles no longer distinguishable from each other, constitutes extensive cratonic units at the base of the various continents. They can be divided into the various Shields found in North America, Scotland, Asia, Australia, etc, that is, the set of various tectonic units making up the mountain ranges of the Prepaleozoic.
From the earliest geological studies, the hypothesis that the prepaleozoic substrate had formed on a global surface embracing the whole Earth was questioned, also because for some centuries it had been found that many coasts of the continents could fit together, despite the fact that they were thousands of kilometers apart. between them. Furthermore, with the continuation of the geological studies it was found that various geological formations, also on the basis of the content of the fossils, could be correlated on both sides of the oceanic areas. There were various hypotheses to explain what was found in the research, but to arrive at an explanation on the mechanism of the phenomenon it was necessary to wait until 1915 by Alfred Wegener, meteorologist, father of Continental drift theory who argued that continents move mainly due to centrifugal forces due to the rotation of the Earth. Wegener's theory, although it represented a significant step forward in the explanation of the phenomenon, did not meet the favor of scholars as it was objected that the earth's crust was too rigid to allow a continental drift and also the centrifugal force was too weak to win. the resistance offered by the base to the movement of enormous masses such as continents.
However, the studies led to a first conclusion: the current continents, or perhaps more precisely the current large terrestrial plates, once had to be part of a single continent that stretched from one polar end to the other, not necessarily coinciding with the current ones. poly.
It remained only to demonstrate how the separation of the plates had occurred. The explanation came only a few decades ago and, unexpectedly, not as a result of research on land, but on the bottom of the oceans.
In fact, before such research it was logical to believe that the ocean floor must have been the place of accumulation of enormous quantities of sediments coming from the washout of the emerged lands, distributed and leveled by the ocean currents known for some time. The oceanographic surveys instead highlighted deep incisions separated by more pronounced reliefs than those of the emerged lands, affected by complex systems of fractures, as can be easily observed in any recent terrestrial atlas.
Another unexpected information is that relating to the intense volcanic activity of the ocean floor, characterized by the outflow of basalts along the oceanic ridges with consequent growth of the ocean floor whose expansion actually generates lateral thrusts towards the terrestrial plates, moving away from each other.
In summary, Wegener's theory of the Drift of the Continents after 50 years finds its rehabilitation if it is specified that the displacement of the Continents does not occur by movements between them and the underlying rigid substrate of the earth's crust, but between the whole lithosphere complex and the mantle, where the high temperatures make the material fluid and therefore with a low coefficient of friction with respect to rigid moving masses above.
For a clearer graphic representation of the phenomenon of the Drift of the Plaques we used the maps published in the Study " Continental drift and plate tectonics "made by Città dei Ragazzi.
As schematically indicated in the table on the side, the distribution of the plates embraces the whole globe and the distribution of the volcanoes along the fracture lines and the edges of the plates is very clear.
The outflow of basalt along the longitudinal ridges of the ocean trenches, in exerting pressure against the walls of the plates that delimit the trenches, causes the oceans to widen more and more at the rate of a few centimeters a year. On the basis of this finding that it is calculated that the formation of the current oceans took place 200 million years ago, that is, when the current continents were a single block called Pangea.
However, it is believed that the process of the Zolle drift has always existed and that it has affected the entire stratigraphic complex of the Prepaleozoic. However, what concerns us a little more closely is the current cycle that began at the end of the Paleozoic. Geological studies are increasingly confirming the gradual process of separation of the various continents, which, dragged by the rigid substrate, have assumed the current reciprocal position
The geological study is increasingly confirming the dismemberment of the continents and the topicality of the mechanism of the Zolle Drift. As we will see in continuing the journey we have undertaken, we will see that all the tectonic phenomena are linked to it, so much so that we will see Africa disappear under Europe and many other events considered exceptional in many ways.
Dr. Pio Petrocchi