Continental drift theory of A. Wegener
- 1. Chapter 3 The Origin of Ocean Basins ©2003 Jones and Bartlett Publishers 2 The Origin of Ocean Basins Mr. Toradmal Agastirishi B. Asst. Professor . Department of Geography Dada Patil Mahavidyalaya, karjat, Dist- Ahmednagar
- 6. All previous hypotheses and theory dealing with the origin of ocean basins have rejected after the postulation of Continental Drift Theory Sea Floor - Spreading Plate Tectonic theory
- 8. INTRODUCTION Prof. Alfred Wegener was German meteorologist. He propounded his continent drift in 1912 but it could not come in light till 1922 when he elaborated his concept in book entitled “ Die Entstehung der Kontinente and Ozeane “ ( The origin of continents and Oceans ) which was translated in English in 1924.
- 9. Basic Premise of Theory Wegener believed in Three Layers System of earth . 1. Sial – Outer layer 2. Sima – Intermediate layer 3. Nife – Lower layer
- 10. According to Wegener sial was represented the continental masses whereas the ocean crust was represented by sima. Continents or sial were floating on sima. Basic Premise of Theory
- 11. Basic Premise of Theory PANGAEA ( SUPERCONTINENT ) Wegener assumed , on the basis of evidences of Palaeo-climatology, Paleontology, palaeobotany, Geology and Geophysics, that all the landmasses were united together in the form of one landmass which he named Pangaea which was surround by a huge water body, known as Panthalasa.
- 13. Super-Continent PANGAEA = Gondwanaland + Laurasia Super- continent Pangaea was broken into two parts in Triassic period (200 million years ago ) LAURASIA – The northern part of Pangaea comprised N. America, Greenland, Europe and N . Asia. GONDWANALAND – The southern part of Pangaea comprised S. America, Africa Antarctica, Australia, and Peninsular of India. TETHYS- These two parts were separated by a long shallow sea called the Tethys
- 37. Force Responsible for the Continent Drift According to Wegener after breaking Pangaea drift in two directions Equator ward movement – The equator ward movement was caused by gravitational differential of force and force of buoyancy. West ward movement – The west ward movement of continents was caused by the Tidal force of the Sun and the Moon
- 38. Evidences in Support of the Theory 1. GEOGRAPHICAL SIMILARITY ( Jig-Saw-Fit ) 2. GEOLOGICAL EVIDENCES 3. PALAEONTOLOGICAL EVIDENCES 4. GEODETIC EVIDENCES 5. BIOLOGICAL EVIDENCES 6. PALAEOCLIMATIC EVIDENCES
- 39. GEOGRAPHICAL SIMILARITY ( Jig-Saw-Fit ) South America Africa According to Wegener there is geographical similarity along both the coasts of Atlantic Ocean. The eastern coast of S. America can be fitted into the western coast of Gulf of Africa Wegener called it “ Jig=saw-Fit “
- 41. GEOLOGICAL SIMILARITY Geological evidences denote that the Caledonian and Hercynian mountain systems of the western and eastern costal area of the Atlantic are similar. The Appalachians Mt. System of N. America are same with the Mt. systems of Ireland, Wales and NW Europe.
- 42. PALAEONTOLOGICAL EVIDENCES Distribution of Fossils There is marked similarity in the fossils and vegetation remains found on the eastern coasts of S. America and western coasts of Africa.
- 43. GEODETIC EVIDENCES It has been reported form geodetic evidences that Greenland is drifting westward at the rate of 20 cm /year, after 1960s Sea-floor spreading have confirmed the movement of Greenland.
- 44. BIOLOGICAL EVIDENCES The Lemmings (small size animal) of the northern part of Scandinavia have a tendency to run westward , when their population is increased but they were fall in the sea water due to absence of any land This behavior of lemmings proved the fact that the landmasses were united in the ancient time. The distribution of Glossopteris flora in India, S. Africa, Australia, Antarctica, Falkland islands etc. proves the fact that all the landmasses were previously united in the form of Pangaea .
- 46. PALAEOCLIMATIC EVIDENCES Ancient Glaciations The evidences of Carboniferous Glaciations of Brazil, Falkland, S. Africa, peninsular India, Australia, and Antarctica further prove the unification of all landmasses in one landmass (Pangaea) during Carboniferous period.
- 47. Criticism of the Theory 1. The force applied by Wegener ( Differential Gravitational force and Buoyancy and Tidal force of the Sun and Moon ) are not sufficient to drift the continents so apart, and continents would need Tidal force to be 10,000 million times as powerful as it is at present , if it had it would stop the earth’s rotation within year. 2. Both the coasts of the Atlantic Ocean can’t be completely refitted. Thus ,the concept of “ Jig-Saw-Fit “ can’t be validated.
- 48. Criticism of the Theory 3. Wegener has not the elaborated the directions and chronology sequence of the displacement of the continents. 4. He did not described the situation of pre – Carboniferous time. Thought most points of Wegener ‘s Theory was rejected but its central theme ( Displacement of continents ) was retrained .
- 49. Continental Drifting and Origin of Ocean Basins The disruption, rifting and displacement (Drifting) of continents began from Carboniferous Period to Pliocene Period. According to Wegener that all the landmasses were united together in the form of one landmass which he named Pangaea (About 200 million years) which was surround by a huge water body, known as Panthalasa. Formation of Tethys Sea Super- continent Pangaea was broken into two parts in Triassic period (200 million years ago ). LAURASIA – The northern part of Pangaea comprised N. America, Greenland, Europe and N . Asia and GONDWANALAND – The southern part of Pangaea comprised S. America, Africa Antarctica, Australia, and Peninsular of India. These two parts were separated and space was filled up with water body was called Tethys Sea.
- 50. Formation of Atlantic Ocean During Cretaceous period Gondwanaland broke up and Indian peninsula, Madagascar, Australia and Antarctica away from each other due to the impact of tidal force of the Sun and Moon. Similarly , North away from Europe and South America away from Africa and moved westward at different rate while Africa moved toward east and ‘S’ shape of Atlantic Ocean could be possible. Formation of Indian Ocean In Cretaceous period Gondwanaland broke up and Indian peninsula, Madagascar, Australia and Antarctica away from each other due to the impact of tidal force of the Sun and Moon. Due to the northward movement of Indian peninsula , eastward movement of Australia and southward movement of Antarctica Indian Ocean was formed.
- 51. Formation of Pacific Ocean The size and shape of the Panthalasa was reduced due to the movement of continent from all sides toward Panthalasa. Thus the reaming portion of Panthalasa became the Pacific Ocean. Formation of Arctic Ocean Arctic Ocean was formed due to the outward movement of continental blocks from north pole. According to continental Drift theory it may be point out that Ocean basin were formed because of drifting of continents from Carboniferous period to Pliocene period when present pattern of ocean basin was attained.