Continental Drift Theory by Alfred Wegener
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Continental Drift Theory by Alfred Wegener
The continental drift theory hypothesised the distribution of the oceans and continents on Earth surface.
The idea of lateral movement of continents or continental drift was put forward in 1912 by Alfred Wegener in a book The Origin of Continents and Oceans.
It is said that continents were gradually and slowly drifting apart or separate and moved towards their present day location is known as Continental Drift.
This theory claimed that the changes in the appearances of the Earth were, largely, due to the shifting of continents. It states that SIAL comprising the continents, is floating over SIMA, comprising the upper portion of the sea floor.
Pangea & Panthalasa:
About 250 million years, ago there was only one super-continent called Pangea and one super-ocean called Panthalasa.
Pangaea consisted of North America (with Greenland attached) and Eurasia (minus Arabia and India) in the extreme North and below it, South America and Africa (with Arabia attached and further down Antarctica, Australia and India.
Angaraland/Laurasia & Gondwanaland:
About 200 million years ago the Pangaea was broken into two parts. One of the parts started floating Northward whereas the other part Southwards. The Northern part was known as Angara land (Laurasia) and the Southern as Gondwana land.
Tethys Sea:
The intervening space between these two giant continental blocks was filled up with a narrow and shallow water body known as Tethys Sea.
Angaraland/Laurasia & Gondwanaland:
Laurasia consisted of present North America and Greenland and Eurasia (without India and Arabia), while Gondwanaland contained Africa with Arabia attached, South America, Australia and India represented the Southern part of Pangaea. South Pole was located near Durban, in South Africa.
Later on, the further disruption of the Gondwanaland occurred during Jurassic period.
According to Wegener, Forces responsible for this Continental Drift:
Gravitational Forces:
The Northward movement was caused by gravitational forces i.e, because of intense gravitational pull of the poles.
The Northward movement of India and Africa caused the sediments deposited in the Tethys to be crumpled and deformed and thus, the Alpine and Himalayan mountain ranges were formed.
Tidal Forces:
The Westward movement was caused by tidal forces. The Westward movement of Americans led to the formation of Andes and Rockies and the Caribbean island.
The forces responsible for drifting of continents that suggested by Wegener were polar-fleeing forces relates to the rotation of the Earth and tidal force caused by the attraction of the Moon and the Sun.
Most scholars considered these forces inadequate for continental drifting.
Evidence in Support of the Continental Drift Theory:
Wegener cited various evidences to show that the continents could have been close together in the past. They were as follow
- Juxta Fit of Continents (Jigsaw-fit).
- Structural and Stratigraphic Evidences.
- Fossil Evidences.
- Placer Deposits Evidences.
- Coal Deposits Evidences.
- Palaeoclimatic Evidence.
Jig-Saw Fit of Continents:
The coastlines of Africa and South America facing each other have a noticeable and accurate match. Both the opposing coasts of the Atlantic Ocean can be fitted together in the same way as two cut off pieces of wood.
Structural and Stratigraphic Evidences:
The radiometric dating methods developed in the recent period have helped in matching the rock formation from different continents across the vast ocean. In North-Western Africa and Eastern Brazil both 550 million years old rocks lie adjacent to rocks dated more than 2 billion years in such a manner that the line separating them is continous, when the continents are brought together.
Fossil Evidences:
Mesosaurus was an aquatic reptile adapted to shallow brackish water. The skeletons of these animals are found only in two places: the Southern Cape Province of South Africa and Iraver formations of Brazil. The two places presently are 4800 km apart with an ocean in between them.
The fossil fern, glossopteris, is widely distributed in Africa, Australia, India, South America and Antarctica. These fossil ferns, which graw only in subpolar climate, are today found in warm climate regions separated by wide oceans.
Thus, it can be inferred that they were associated with a super-continent where fairly cool climatic conditions existed.
Placer Deposits Evidences
Placer deposits. i.e. occurrence of rich placer deposits of gold in Ghana coast with absence of source rocks in the region which are abundance in Brazil evidented the fixing of continents in past
Coal Deposits Evidences
Similar coal deposits in either side of Atlantic Ocean and coal deposits in continental interior and evidences.
Palaeoclimatic Evidence:
Layers of glacial deposits i.e., tillites, striations and grooved marks are found in tropical regions of South America, South Africa, Australia and India (Talcher).
Later plate tectonics theory developed over the idea of continental drift hypothesis and found continents not floating over oceans, but plates containing both continent and ocean floor float over aesthenosphere.
Continental Drift Theory in Short/ Gist of the Continental Drift Theory
OR
Summary/Short notes on Continental Drift Theory by Alfred Wegener
Continental Drift theory by German meteorologist Alfred Wegener in 1912 in his book”origins of oceans and continents”.
Father of Continental Drift theory-Alfred Wegener.
Pangea- Super Continent
Panthalasa- Super Ocean
Tethys Sea- Between Gondwana and Laurasia
Laurasia:Nothern Parts/Continents of Present day Earth Surface (North America, Greenland & Eurasia (without India & Arabia),
Gondwanaland:Southern Parts/Continents of Present day Earth Surface (Africa, Arabia, South America, Australia, and India)
Forces responsible for this Continental Drift
Gravitational Forces: Northward Movement (Towards Equator)
B. Tidal Forces: Westward Movement
Evidence in Support of the Continental Drift Theory:
- Juxta Fit of Continents
- Structural and Stratigraphic Evidences
- Fossil Evidences
- Placer Deposits Evidences
- Coal Deposits Evidences
- Palaeoclimatic Evidence
PAPER 2 JULY 2018
Q.1 Which one of the following phenomena plays a vital role in the dispersion of majestic dinosaurs?
(1) Volcanic eruption
(2) Zonal faulting
(3) Global cooling
(4) Continental drift
Q.2 Which of the following are evidences in favour of the continental drift theory?
(a) Zig-saw fit
(b) Trans – current faults
(c) Fossils in different areas
(d) Convection in mantle
Codes:
(1) (a) and (c)
(2) (a) and (d)
(3) (a) and (b)
(4) (a), (c) and (d)
Q.3 Which among the following is one of the forces responsible for continental drift according to Wegner ?
(A) Tidal force
(B) Convection currents
(C) Tensional force
(D) Compressional force
Q.4. Match List – I with List – II and select the correct answer from the codes given below :
List – I
(Theories)
(a) Continental Drift theory
(b) Sea floor spreading theory
(c) Convection Current Theory
(d) Elastic Rebound Theory
List – II
(Propounders)
(i) Harry Hess
(ii) Reid
(iii) Wegener
(iv) Holmes
Codes :
(a) (b) (c) (d)
(A) (iii) (i) (iv) (ii)
(B) (i) (ii) (iv) (iii)
(C) (iv) (i) (iii) (ii)
(D) (i) (iii) (iv) (ii)
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