Distribution Of Oceans And Continents

Abraham Ortelius was a Dutch map maker who first proposed the possibility of Europe, Africa and America having been located side by side.

The polar fleeing force elates to rotation of the Earth. The Earth has a bulge at the equator, this is due to the rotation of the Earth.

Antarctica and the surrounding oceanic plate is a tectonic plate and therefore it is a massive plate

Volcanic activities, age of rocks from the ocean floor and other facts were discussed by those while discussing the concept of sea floor spreading. However there was no fact discussed related to fossils lying in the rocks.

The Indian plate contains Indian Peninsular regions as well as Australian continental portions. The type of boundary or subduction zone along the Himalaya Mountains was formed as continent-continent convergence.

(i) There were two types of forces as suggested by Wegener for the movements of the continents.

• Polar feeling force- It relates to the rotation of the earth. The Earth has a bulge at the equator due to his rotation of the Earth.

• Tidal force- It is the force developed due to the attractive pull by the Sun and the Moon which develop tides in ocean water.

Wegener believed that these two forces would continue for millions of years.

(ii) The conventional currents are generated due to presence of a radioactive element causing thermal differences in the mantle portion. That is the hot material rises up and the cold thing sinks down. Holmes said that these forces were present throughout the mantle.

(iii) Transform Boundary- When the crust is neither destroyed nor produced as the plates slide horizontally past each other. Then it is called transform boundary.

Convergent Boundary- When the crust is destroyed as one plate dived under another, then it is called convergent boundary

Divergent Boundary- When new crust is generated as the plates pull away from each other, then it is called divergent boundary.

(iv) When the Indian plate moved towards the Eurasian plate, the outpouring of lava and the formation of Deccan Traps took place. This started 60 million of years ago and continued for a long time and the subcontinent was still close towards the equator.

The evidences in support of the drift theory:-

• The matching of continents (Jig-Saw fit)- The shorelines of Africa and South America made a remarkable and unmistakeable picture perfect match.

• Rocks of same age across the oceans- The radiometric dating correlates the rock formation of different countries. The 2000 million year ago rocks of Brazil matches with that of Western Africa. The marine deposits of America and Africa were of the Jurassic age and prior to that no ocean was present.

• Tillite- It is the sedimentary rock formed out of glaciers. The Gondwana sediments from India had its counterparts in six different landmasses in the southern hemisphere. It now indicates extensive and prolonged glaciations. It delivers unambiguous evidence of palaeoclimates and drifting of continents.

• Placer Deposits- The vast occurrence of gold in the Ghana coast and no rock is amazing fact. The gold bearing veins were in Brazil and it was obvious that gold deposits of Ghana were derived from Brazil plateau as they were side by side.

• Distribution of Fossils- When identical species of plants and animals adapted to living on land or in fresh water are found on the side of the marine barriers, a problem arises regarding accounting for such distribution. The observation that Lemurs occur in India, Madagascar, Africa conveyed a continuous landmass Lemuria linking to three landmasses. Some skeleton were also found.

(ii)

(iii) The major post-drift discoveries that rejuvenated the interest of scientists in the study of distribution of oceans and continents:-

• Along the mid-oceanic ridges, volcanic eruptions were common and they bring lava on the surface of the earth.

• The rocks equidistant on either side of crest of mid-oceanic ridges show remarkable similarities in terms of period of formation, chemical composition and magnetic properties. The age of rocks increases as one move away from the crest.

• The ocean crust rocks are younger than the continental rocks.

• The sediments on the floor were unexpectedly very thin.

• The deep trenches have deep seated earthquakes while in the mid oceanic ridge areas, the quake foci have shallow depths.

The stripes of normal and reverse magnetic field that parallel the mid-oceanic ridges which enable to read the rate of plate movement. These rates vary considerably.