Important geographical phenomenon
- In order to understand important geographical phenomenon of geography, as per the syllabus of GS it is necessary to understand the origin of continents and ocean basins.
- Continent and ocean basins are fundamental relief feature of the globe.
- They are considered as relief features of the first order, and different theories regarding the origin of the continents and oceans are being put forth by the scientists.
- About 70.8 percent of the total surface area of the globe is represented by the oceans and 29.2 are represented by the continents.
Distributional pattern of the continents and ocean basins
- There is overwhelming dominance of land areas in the northern hemisphere; more than 75% of total globe is situated to the north of the equator.
- Continents are arranged in roughly triangular shape; most have their bases (of triangle) in the north while their apices are pointed towards south.
- The oceans are also triangular in shape, contrary to the continents the base of oceans is in the south while their apices are in the north.
- The North Pole is surrounded by oceanic water, while South Pole is surrounded by land area (of the Antarctic Ocean).
- There is antipodal situation of continents and oceans, only 44.6 percent oceans are situated opposite to oceans.
- 4 percent of the total land area of the globe is opposite to land area; more than 95% of the total land area is situated opposite to water bodies.
- The great Pacific Ocean basin occupies almost one – third of the entire surface area of the globe.
The above mentioned characteristic would help us to validate the authenticity of any hypothesis or theory dealing with the origin and evolution of the continents and ocean basins.
There are various hypotheses regarding the origin of the earth, but we would discuss the following one, they are considered to be much more scientific.
- Tetrahedral hypothesis postulated by Lowthian Green
- Continental drift theory of Taylor
- Plate tectonic theory
- Sea floor spreading
- It is based on the fundamental principles of geometry
- Elie de Beaumont is considered to be first the attempted in this field
- But the theory of Lowthain (in 1875) is most significant of all hypotheses based on gromatric principles.
- He based his hypothesis on the two basic principle of geometry
(i) A sphere is that which contains the largest volume with respect to its surface area
(ii) A tetrahedron is that body which contains the largest volume with respect to its surface area.
- It 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. He postulated it after considering the characteristics of the distributional pattern of the land and water over the globe.
- There is dominance of land area in the northern hemisphere and water areas in the southern hemisphere
- Triangular shape of continent and oceans,
- 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
- Antipodal arrangement of continent and oceans
- Largest extent of Pacific Ocean covering one third area of the globe
- Location of chain folded mountains around Pacific Ocean.
- According to him when earth was originated it was in sphere form
- In the beginning earth was very hot but it gradually began to cool down due to loss of heat.
- First the quarter part of the earth cooled down and thus was formed the crust but the inner part was continued to cool down
- Consequently the inner part of the earth was subjected to much more contraction, thus there was marked reduction in the inner part of the earth.
- Upper part of the earth (crust) was already cooled down, and 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.
- He also clarified that due to structural variations; there may be some deviations from a true tetrahedron.
- Four oceans (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 retain water because of the fact that these were lower than the level of the apices or coigns of the terrestrial tetrahedron.
Fig- Distribution of land and water on a tetrahedron
- To major extent it successfully explains the characteristics feature of the distributional pattern of the present day continents and ocean basin.
- But because of certain basic defects and errors the theory is not acceptable to the modern scientific community.
- It is argued that balance of the earth in the form of a tetrahedron while rotating on an apex cannot be maintained.
- The earth rotating so rapidly on its axis that the spherical earth cannot be converted into a tetrahedron while contracting on cooling.
- This hypothesis believes more or less in the permanency of continents and ocean basins, while plate tectonic theory has validated the concept of continental drift.