CONTINENTAL DRIFT THEORY BY ALFRED WEGNER
HISTORICAL BACKGROUND
The Unification of the continents and oceans are not a new concept. The Scientists and Scholars wondered about the shape of the south america and Africa More than 400 million years ago, many scientist started to think about the earth's positions. If South America and Africa come to together ,it fits perfectly.
ABRAHAM ORTELIUS in 1596 first talked about the positions of the continents and oceans.
Following by him sir FRANCIS BACON in 1620 and ANTONIO SNIDER in 1858 gave the idea of unity of the earth,
However it was in 1908, F.B.TAYLOR, postulated his concept of "HORIZONTAL DRIFTING OF CONTINENTS". In 1912 ALFRED WEGENER gave his theory on drifting of continents.
ALFRED WEGENER'S CONTINENTAL DRIFT THEORY
Wegener's theory was mainly based on the problem solving theory. Before Wegener, there are numbers of concepts ,works and findings. Wegener assumed that the climatic change might be related to it because there are various evidences that related to the climate change. In fact ,"The continental drift theory grew out the need of explanation the major variation in climate in past"
ROLE OF CLIMATE
1. Continents remains stationary at their place and climate shifts from one place to other.
2. The climatic zone remains stationary and the continents moves.
MAIN CONCEPT:
Wegener said that all continents could be united together in a form of super continents.He believed that earth crust made of SIAL and SIMA continents are floating into ocean.He said that the continents are together in united form called as PANGEA which means " all land".and the ocean around pangea called PANTHALASSA.WEGENER stated that all the continents could be United together in a form of supercontinent.He believed that the earth's crust was made of sima and sial .The ocean crust was being made of heavier than Continental crust and situated below the Sial or Continental crust.about 300millons years ago the continents were together in form called as Pangea ,the ocean around it called panthalassa.In different geological era,the continents were drifted and formed present condition of earth.Drifting of continents according to geological era as following.
DRIFTING OF CONTINENTS ACCORDING TO GEOLOGICAL
TIME SCALES
- In Carboniferous era the south
pole was near the south Africa coast and the pacific ocean in
north pole.
- In Mesozoic era Pangea started
to split into two proto continents i.e LAURASIA and GONDWANA. Laurasia
consisted of North america,Europe,Greenland,and Asia excluding India.
Gondwana in southern continents consisted of India,South america ,Africa
and Australia.
- By the end of Cretaceous
era,the continents were seperated into landmasses and form present
day continents.
- wegener assumed the continents were moved horizontally on seafloor .due to movement of the continents ,the folded mountain formed.
WHY CONTINENTS WERE MOVED?
Wegener started that
there must be some mechanisms that drifted the continents. He stated that the
ocean is being lesser materials situated below the heavier materials. Therefore two mechanisms that moved to help the continents was
- Centrifugal Force : Wegener believed that the centrifugal forces which creates the spinning of
the earth on its own axis.the breaking of continents in past was caused of
centrifugal force and pushed continents towards the pole
- Tidal Force: tidal forces are
causing of the movement of continents towards westward.
EVIDENCES SUPPORT TO THE THEORY
WEGENER had proved that the unification of the continents in a form of a single masses during Carboniferous age.
Jig Saw Fit
According to WEGENER,
the west part of the Africa and the eastern part of South America are fitted
together and both parts of the coast are similar Geographically.
Similarity of Physical Features
Caledonian mountain and Hercynian mountain in Europe and Appalachian mountain in USA seems to be one continents in the past.On the other side,Greenland and Ellesmere and Baffin island fits in well
Distribution of fossils of Plants and Animals:-
There are similarities of plants and animals found in
the past history.According to WEGENER ,The Unification of Landmass helped
animals to travel from one region to another.
Following are examples
of fossils
CYNOGNATHUS,a Triassic land reptile found in South America and Africa
LYSTROSAURUS,a Triassic land reptile found in Africa,India and Antarctica.
MESOSAURUS, a freshwater reptile found in southern part of South America and South Africa
LEMURS found in India, Madagascar and Africa
GLOSSOPTERIS,a fossil plant found in South America, Africa, Antarctica, India and Australia.
Contemporary
Stratigraphy:-
There is marked that
similar Rocks found in South America and Africa,the similar sequence of
Appalachian mountain and Caledonian mountain in North America and Europe
respectively.
ICE MATCH
The evidence of
Carboniferous glaciation, Brazil, India, Australia and Antarctica was one
landmass. On the other side Glacier stratification shows that radiated outward
from the glacier Centre over the South Pole in Africa toward the Atlantic Ocean
and from the Atlantic ocean onto South America. Therefore, the continents must
be joined so that the ice moved across a single land Mass Pangea. The glacier
evidences Support the polar wandering.
DRAWBACKS
Some drawbacks of
WEGENER'S theory of Continental drift
1. Concept of Jigsaw Fit:- WEGENER stated that Eastern part of South America and Western part of Africa fits perfectly.but there was difference of 16° angle between them,
2. Fail to explain the mechanism of drifting:- WEGENER explained that continents moved due to tidal forces and centrifugal forces.But the forces would not be strong that continents could be moved.
3. Distribution of fossils:- According to WEGENER , GLOSSOPTERIS found in South America, Africa,Antarctica, India and Australia. But fossils of glossopteris also found in Siberia, North West Afghanistan,NorthEast Punjab etc.
4.WEGENER failed to explain why continents started to move in Mesozoic era,He didn't explain about the movement of continents before.
CONCLUSION: There is some drawbacks of continental drift theory but it is considered as most compact theory of continental drift.thats why it is so important concept.
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