There are many relief features on Earth, which can be classified into three categories. The first-order relief features include continents and oceans. The second-order relief features include mountains, plains, and plateaus, which are formed by internal movements of the earth and exogenous waters. The third-order relief features include valleys, hills, deltas, and glaciers, which are formed by the forces of erosion, such as flowing water, wind, and waves.
- Explain the meaning of Physical Geography. Explain its Scope and Importance.
- Discuss the nature and Scope of Geomorphology.
Continents and oceans are considered the two main forms of the Earth’s surface. The distribution of these two forms of crust can provide insights into their origin, which is a complex and controversial subject. Many scholars have expressed their views on when and how the continents and oceans originated. The following characteristics of the distribution of continents and oceans can be observed from the study of the globe:
- Most of the continents are in the Northern Hemisphere, and most of the oceans are in the Southern Hemisphere. However, the opposite is true near the pole regions. Oceans are located near the North Pole, and continents are located near the South Pole.
- The Land Hemisphere covers 81 percent of the land, with its pole located in Brittany, which includes parts of North America, Europe, Asia, Africa, and South America. On the other hand, the Water Hemisphere is dominated by water, with its pole located around New Zealand. The shape of continents widens towards the north and narrows towards the south, except for Australia. Similarly, oceans narrow towards the north and widen towards the south.
- The anti-diameter relationship between water and land on the surface is also a characteristic of their distribution. Seas cover 46.6 percent of the surface area, but only 1.4 percent of the land area is surrounded by land. Around 5 percent of land is surrounded by the sea.
The interior of the Earth is still warm and slowly cooling down. Based on this assumption, the British mathematician Lothian Green presented his tetrahedral hypothesis. Green considered the distribution of continents and oceans as a tetrahedron, around which flows occur in three directions, surrounded by four figures of equal sides. The shape of the tetrahedron is clear from the picture, which shows three flattened parts in the shape of an isosceles triangle, giving the impression of the North Atlantic Ocean and the Indian Ocean. The fourth flat part is not visible in the figure, from which the Pacific Ocean is displayed. However, the raised parts of this figure indicate the sides of the triangular flattened parts, describing the position of the continents.
According to Lothian Green, the effect of pressure on any round, soft object changes its shape to that of a tetrahedron. He assumed that with the cooling of the Earth, the inner part of the Earth contracted faster than the outer part, i.e., the volume of the inner part decreased. The upper surface was already solid and hard, so it could not shrink, causing a difference between the inner and outer layers of the Earth. In such a state, the Earth has to come in the shape of a tetrahedron whose volume is small even though the surface is large. In the opinion of scholars, such a shape can only be quadrilateral.
If the area of the sphere and the tetrahedron are equal, then the volume of the tetrahedron will be less than the volume of the sphere. According to this belief, the Earth has not yet reached the shape of a perfect tetrahedron, but as it is getting colder, the shape of the tetrahedron is becoming complete. Due to the effect of the force of attraction, the upper crust settled in the shape of the inner tetrahedron, which gave rise to the oceans and continents. Due to the shrinking of the inner parts, the troughs formed by the uneven inward sinking of the outer layers formed the sea parts, which corresponded to the flat surface of the tetrahedron, and the corners and sides corresponded to the continents.
Combining this idea with the above figure, it is known to be correct because if the tetrahedron is immersed in a globe of water, then the water will come on the sticky part soon, but the raised part will remain outside the water, which respectively points to the sea and land. Even if the Earth is considered the base of the tetrahedron, part of its edges and corners will force them to sit down and rise, and an attractive revolving Earth will be formed.
Criticism of the Tetrahedral Hypothesis
The following are criticisms made by various scholars. Although this idea was recognized for a long time, it started receiving criticism in the last century. Scientists argue that the shape of the rotating Earth cannot remain as a tetrahedron because it is an unbalanced shape. At the same time, it is also unlikely for the Earth to assume the form of a tetrahedron due to the high speed of the moving Earth. According to the principle of the tetrahedron, the most terrestrial part should be at 300 N latitude, but in reality, the terrestrial portion is 80.1 percent at 600 30 latitudes and only 43.6 percent at 300 30 latitudes. The southern part of the continents should be at a distance of 1200, but in reality, this is not the case.
British scientist Gregory presented some geographical conditions of the surface in confirmation of this hypothesis. In the northern hemisphere, there is more land, and the shape of most geographical objects is triangular. The parts of the land protrude towards the south, and the seas become narrower towards the north. The anti-diameter relationship between the sea and land parts is described by the tetrahedron by the said scholar. Additionally, the continents of Asia and North America meet each other by making an angle of 1200, and an external angle is formed on the sides of the tetrahedron.
The German geologist Suess proposed that the Earth’s surface is composed of two types of rocks: resistant and non-resistant. The resistant rocks are old and hard and do not deform easily.
In the Northern Hemisphere, these resistant rocks are found in three areas. The first area is in Laurasia, which includes eastern Canada and the western islands of Scotland. The second area is the Baltic Shield, which includes the regions around the Baltic Sea. The third area is Angaraland, which includes eastern Siberia and China. In the Southern Hemisphere, the resistant rocks are found in Gondwanaland, which includes Brazil, Africa, Arabia, India, China, and the western plateau of Australia.
The weaker intermediate surface between these resistant rocks could not bear the heavy load, and thus bending occurred. This occurred at different times, with periods of stability between each bending event. Cracks developed in the upper parts of the resistant rocks, causing large portions of the crust to sink and form oceans.
The Atlantic Ocean was formed due to the breakup of Laurasia and Gondwanaland. Between the resistant parts of Asia, Europe, and Africa, there were areas of non-resistant rocks. Before the third folding event, a sea called Tethys existed in this area, remnants of which can still be seen in the Mediterranean Sea. The pressure exerted by the resistant parts on both sides of Asia and Europe led to the formation of new fold mountains. Continents were formed from the raised portions of both resistant and non-resistant rocks during bending events, while submerged portions formed oceans due to cracking.