Earth (Part-2)

1.3 DISTRIBUTION OF OCEANS AND CONTINENTS

The earth’s surface is covered with Continents and Oceans that are known as “first order relief features”. Continents cover 29% of the earth’s surface whereas oceans cover 71% of the earth’s surface. They are also not uniformly distributed among the northern and southern hemispheres. More than 75% of land dominates north of the equator. Thus, the northern hemisphere would be the ‘Land Hemisphere’. Contrary to this, water bodies dominate in the southern hemisphere. Thus, the southern hemisphere would be the ‘Water Hemisphere’. The north pole is surrounded by oceanic water whereas the south pole is surrounded by the land area of Antarctica. The area covered by the Pacific Ocean basin is one-third of the total area of the earth’s surface.

                

1.3.1        CONTINENTAL DRIFT THEORY

“The continental drift theory” was propounded by Alfred Wegener, a german meteorologist, in 1912.This theory was regarding the distribution of oceans and continents. According to Wegener, all the continents joined together and formed a supercontinent Pangaea which is all land surface of the earth. The land mass is surrounded by mega-ocean Panthalassa, referred to as all water surface of the earth. He further argued that, around 200 million years ago, the supercontinent (Pangaea) started splitting into two parts Laurasia and Gondwanaland forming northern and southern continents respectively. Eventually, these two major continents split into present-day continents.

NOTE-

Abraham Ortelius, a Dutch map maker, considered the possibility of Europe, Africa, South America, and North America have been located side by side. He proposed such a possibility as early as 1596.

Antonio Pellegrini drew a map showing four continents (two Americas, Europe, and Africa)  together.

Evidence in support of the Continental Drift

  • The Jig-Saw-Fitting

There is geographical similarity along both the shoreline of Africa and South America. Both continents can be fitted together as they were earlier. Geologically, the Caledonian and Hercynian mountain systems of the western and eastern coastal areas of the Atlantic oceans are identical. The Appalachians of the northeastern region of North America are compatible with the mountain systems of Ireland, Wales, and north-western Europe.

  • Distribution of Fossils

When identical species of plants and animal fossils were found on the eastern coast of South America and the western coast of Africa, a problem arises while accounting for such distribution because both the landmasses are divided by a great marine barrier.

  1. The remains of Lemurs found in the foothills of Shivalik are one of the fossil evidence because nowadays these primate animals are found in Madagascar and there is a marine barrier between India and Madagascar. Thus, some believe that there is a continuous landmass “Lemuria” that links India, Madagascar, and Australia. But in the present day, it is submerged underwater (Indian Ocean).