CONTINENTAL DRIFT

·     According to Alfred Wegener, the entire landmass of the globe was together about 280 million years ago.

·     It was termed as Pangea, a super continent.

·     The huge water body surrounding the Pangea was known as Panthalasa.

·     From 280 to 150 million years ago, Pangea was broken latitudinally into northern and southern parts known as Laurasia (Angaraland) and Gondwanaland, respectively.

·     Both of them drifted away and in between a shallow sea emerged by filling up the water from Panthalasa. It was known as Tethys sea.

·     Later on Laurasia and Gondwanaland rifted and finally drifted to form the present day distribution of land and water on the earth.

Evidences of Drift  :

·     Wegener gave a number of evidences in support of the unification of landmass in geologic past.

·     They are such which cannot be negated even today.

a. Jig-saw-fit:-

·     Eastern coast of South America is identical to Western coast of Africa which fits to a certain depth in the ocean.

·     To a certain extent coastal areas and continental shelves have been modified by oceanic waves through denudation.

b. Geological similarities:-

·     The mountain systems of Southern Atalantic coast in South America and Africa show the similarity of the extension in both continents.

c. Coal and Vegetation evidences:-

·     The distribution of coal and vegetation over South America, Africa, India and Australia proves that they were together in geological past.

·     The classical glacial deposits during carboniferous period over these landmasses resemble each other which tells the story of togetherness.

·     Today they lie in different climatic zones. Apart from above evidences put forward by Wegener, other evidences (known later) are also there which support the idea of continental drift.

d. Evidences from paleomagnetism :–

·     Paleomagnetism is the study of the direction of pole through ages.

·     Magnetically susceptible minerals like haematite, pyrhotite magnetite etc. get aligned with the magnetic pole of the earth and recorded in the solidification of magma during that time.

·     It is found that periodic changes have occurred and poles have wandered which is not possible for the entire earth.

·     Hence, it is the twist and turn of the landblock and not for the entire earth which has again explained that the continents have shifted their positions.

e. Sea floor spreading :–

·     Along the mid Atlantic ridge, magma comes out at the sea bed and gets solidified.

·     A new zone is formed and this process is continuing since millions of years.

·     It is leading for diversion of continental block, and hence the size of the Atlantic ocean is increasing which is termed as sea floor spreading.

·     It is the classical example of the shifting of continents.

·     The explanation of continental drift through sea floor spreading and the study of paleomagnetism is commonly known as Plate Tectonics.