TECTONIC OF PLATES THEORY

This was a very important step, for development of the understanding of the drift of continents theory. Many years ago in 1872 a British expedition discovered in the ocean floor a ridge  along of the center of the Atlantic Ocean,  later there where many other expeditions that discovered the same in Atlantic and Indian Ocean.

After the Second World War more intense expedition began, with more sophisticated equipment major economic resources; Richard Field geologist of Princeton University was one of the precursors, he convinced a group of important geologist to join to this research, wich revealed many details about oceanic ridges. At the geophysics year (1957-1958) the investigations took a new impetus, and revealed that all the ridges was connected passing by all the oceans conforming 65000km submarine ridge, also the investigation revealed the existence of a very wide crack in the middle.

At that time the seismic epicenter was located with more precision, and many coincided with the meso-oceanic ridges, indicating that those were instability zones.

Many interpreted the oceanic ridges as a product of the earth expansion,  however new data were obtained, in 1962 was established that both sides of the Atlantic Ocean were joined 200 million years ago, implying an expansion 300 times faster than calculated by Dicke (precursor of the theory of the Earth expansion), the idea of a growing world was abandoned soon. If the earth would be expanding so fast, that implies that the inertia moment would get higher, and to to preserve the energy the angular velocity of the planet would decrease; and that means today the days would last less than that time, and there was not registers supporting that fact was real.

At 1960 Harry Hess, who was a Richard Field’s student, had conceived a new hypothesis; the theory of Hess was that the convection currents in the mantle caused the magma to ascend in the oceanic ridges, which solidify and form a new crust. In 1962 this theory was called “the expansion of the oceanic floor”, and has been generally accepted, though there was an aspect that has not explanation. It was supposed the oceanic ridges had been formed originally as continuous lines and had acquired its discontinuous shape with the expansion process. In this model the sections of the oceanic ridges are separated by trans-current faults, but the problem was explain the absence of seismic activity at the frontier of these faults. The answer was: the ridges had always had a discontinuous shape and the faults that are separating the extension sections are transformation faults, out of the extension zone there is not differential motion between both faces of the fault.

image taken from Google Earth shows the oceanic ridges in the middle Atlantic Ocean