Q. 35.0( 3 Votes )

Answer the follow

Answer :

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.


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