A few scientists have attempted to solve the problems of the origin of the continents and ocean basins on the basis of fundamental principles of geometry. The pantagonal dodecahedral hypothesis (dodeca is a Greek word which means twelve) of Elie de Beaumont is considered to be the first attempt in this field but the tetrahedral hypothesis of Lowthian Green is most significant of all the hypotheses based on geometrical principles.
‘An attractive hypothesis which has enjoyed a considerable vogue was initiated by Lowthian Green in 1875’. His hypothesis is based on the characteristics of a tetrahedron which is a solid body having four equal plane surfaces, each of which is an equilateral triangle (fig. 5.1).
Lowthian Green postulated his hypothesis after considering the characteristics of the distributional pattern of land and water over the globe.
Barring a few drawbacks and defects the tetrahedral hypothesis successfully explains the following characteristics of the continents and ocean basins:
(1) Dominance of land areas in the northern hemisphere and water areas in the southern hemisphere;
(2) Triangular shape of the continents and oceans;
(3) Situation of continuous ring of land around north polar sea and location of South Pole in land area (Antarctica) surrounded by water from all sides;
(4) Antipodal arrangement of the continents and oceans;
(5) Largest extent of the Pacific Ocean covering one third area of the globe and
(6) Location of chain of folded mountains around the Pacific Ocean.
The hypothesis of Lowthian Green propounded in the year 1875 is based on the common characteristics of a tetrahedron.
He based his hypothesis on the following two basic principles of geometry:
(1) A sphere is that body which contains the largest volume with respect to its surface area;
(2) ‘A tetrahedron is that body which contains the least volume with respect to its surface area’.
After many experiments Lowthian Green opined that a sphere if subjected to uniform pressure on all its sides would be transformed into the shape of a tetrahedron. He applied this principle in the case of the earth. According to him when the earth was originated it was in the form of a sphere. In the beginning the earth was very hot but it gradually began to cool down due to loss of heat.
First, the outer part of the earth cooled down and thus was formed the crust but inner part of the earth continued to cool down. Consequently, the inner part of the earth was subjected to more contraction due to continued cooling and thus there was marked reduction in the volume of the inner part of the earth. Since the upper part, the crust, was already cooled and solidified and hence it could not be subjected to further contraction.
This resulted into possible gap between the upper and inner parts of the earth. Consequently, the upper part collapsed on the inner part and ultimately the earth began to assume the shape of a tetrahedron. Lowthian Green has further maintained that the earth has not been as yet changed into a complete tetrahedron rather as it is being cooled; it is proceeding towards attaining the true shape of a tetrahedron.
He has further opined that the earth cannot be in the shape of a real tetrahedron because of its structural variations and thus it is natural that there may be some deviations from a true tetrahedron.
In a tetrahedron a plane face remains always opposite to an apex or coign. The apex or coign is more sharpened in the case of a real tetrahedron. In the case of the earth oceans represent the plane faces of the tetrahedron and land masses represent the apices or coigns but in the case of the earth the coigns are not much sharpened, rather they are flat and convex. According to Lowthian Green oceans were created on the plane faces of the terrestrial tetrahedron whereas the coigns became continental masses.
Four oceans (e.g., the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic ocean) were created on the four plane faces of the terrestrial tetrahedron. These plane faces could retain water because of the fact that these were lower than the level of the apices or coigns of the terrestrial tetrahedron.
Continents were formed along the apices or coigns of the tetrahedron. This fact may also be proved on the basis of an experiment. If we submerge a tetrahedron in a hemisphere of water, the flat surfaces of the tetrahedron would retain water while the edges or apices or coigns will project above the water.
Lowthian Green claimed to see a tetrahedral arrangement in the distribution of the continents and oceans in such a way that the earth was linked to a tetrahedron having four flat faces and standing on one point (fig. 5.2). The upper flat face represents the Arctic Ocean while the remaining three faces represent the Pacific Ocean, the Atlantic Ocean and the Indian Ocean.
Similarly, three vertical meridional edges represent North and South America, Europe and Africa and Asia while the lower point is represented by Antarctica. Thus, the presence of water around North Pole and the location of South Pole in land area (Antarctic continent) are very well explained on the basis of tetrahedral hypothesis.
Three coigns out of four coigns of four equilateral triangles are located in the northern hemisphere. Only the fourth coign is located in the southern hemisphere. These three coigns present the oldest rigid masses around which the present continents have grown. These three ancient shields are the Laurentian or Canadian shield, Baltic shield and Siberian shield.
The fourth coign or the pivot of the tetrahedron represents the Antarctic shield. The present continents have grown out of these four ancient shields represented by four coigns of the tetrahedron. All the continents developed along the edges of the tetrahedron taper southward and thus triangular shape of the continents is proved. The location of the oceans along four plane faces and the continents along the edges or coigns of the plane faces of the tetrahedron proves antipodal position of land and water.
Though Gregory accepted the tetrahedral hypothesis of Lowthian Green but he suggested certain modifications. According to Gregory due to shrinkage of the earth because of contraction on cooling ‘the portion of the vertical tetrahedral edges should be fairly constant, but three edges around the polar depression might develop sometimes in the northern and at others in the southern hemisphere’.
Though the tetrahedral hypothesis throws light on the problems of the continents and ocean basins and to major extent it successfully explains the characteristic features of the distributional pattern of the present- day continents and ocean basins but because of certain basic defects and errors the hypothesis is not acceptable to the modern scientific community.
It is argued that the balance of the earth in the form of a tetrahedron while rotating on an apex cannot be maintained. Secondly, the earth is rotating so rapidly on its axis that the spherical earth cannot be converted into a tetrahedron while contracting on cooling. Thirdly, this hypothesis believes more or less in the permanency of continents and ocean basins while the plate tectonic theory has validated the concept of continental drift.