Go through these RBSE Class 11 Geography Notes Chapter 5 Origin of Continents and Oceans contain important concepts so that students can score better marks in the exam.
Rajasthan Board RBSE Class 11 Geography Notes Chapter 5 Origin of Continents and Oceans
→ Continents and oceans are the first class relief present on the earth’s surface. The Continental Drift and Plate Tectonic theories have been accepted for their origin.
→ The continents represent the terrestrial part while the oceans represent the aquatic part.
Continental Drift Theory
- The German scholar Alfred Wegener, introduced the Continental Drift Theory in 1912.
- Wegener considered two alternatives to be the main ones for the purpose of rendering his theory. First, if the climatic condition is variable, then the terrestrial part is stable. Second, if the terrestrial part is variable then the climatic condition is stable. Based on the second option, he had set the theory of the displacement of the continents.
- According to Wegener’s Continental Drift Theory, there existed one big landmass which he called Pangaea which was surrounded by one big ocean called Panthalassa.
- He considered Pangaea to be a Sial floating on a high density layer.
- According to Wegner, the land flows towards the equator and towards the west.
- For this flow of continents: (i) Gravity / Flotation force (ii) Tidal force were considered responsible.
- The gravity or flotation force causes the flow of land towards the equator, while the tidal force causes the flow of land towards the west.
- With the separation of North and South America the Atlantic ocean was formed. Being separated from, Australia and Antarctica, the Indian ocean was formed. The remaining part of the Panthalassa was called the Pacific Ocean.
Evidences in Support of the Continental Drift
- Proof of geographical, geological, Geodesical and biological evidences and Paleoclimateogical are found in favour of the continent drift theory.
- In the geographical proofs, the formation of equilibrium in the Atlantic shores, the alignment of mountains and the new folded mountains are the main source.
- The geological evidence included the similarity in structural and stratigraphical similarities. The geodesical evidence included the geo-morphology of Greenland and Canada. The biological evidence included the fossils evidence and bio-diversity.
- The process of mutual matching of the continents is called jig-saw-fit.
Criticism of Continental Drift Theory
- The continental drift theory has been criticized on the basis of geographical, geological, geometric, biological and paleoclimatological discrepancies.
- Non-matching of the Brazilian coast and the, Gulf of Guinea, only the partial similarities in structural and topographical configuration on the Atlantic shores, the effects of gravitational force and the diversity of the organisms have been criticized.
- The word plate was first used by Tuzo Wilson. In this theory, 6 large and 20 minor plates are considered to make up the earth’s crust.
- The main plates include Indian, Eurasian, African, American, Pacific and Antarctic plates.
- There are three types of plates: (i) Continental plate, (ii) Oceanic plate and (iii) Continental-oceanic plate
- The plates have three margins: the constructive plate margins, the destructive plate margins and the protective plate margins.
- The space formed by the divergence of the two plates form a new one. It is called the constructive plate margins.
- The convergence of the plates leads to the disperal/erosion of plates. This is called the destructive plate margins.
- When the plates create neither the erosion nor the formation of new substances, this is called the protective plate margins.
- The motion of the plates is due to radioactivity, convection currents and geothermal energy.
Evidenced of Plate Tectonics
- Sea floor spreading, continental drift, widening of the river valleys, etc. are considered to be the evidences of plate tectonics.
- Expansion of the ocean bottom proves the concept of plate tectonics.
- Paleomagnetism and sea-bottom transmission have proven mobility in the land.
- The width of valleys, seismic events, volcanic activity and mountain formation process also certify plate tectonics.
Origin of Continents and Oceans Notes Important Terms
→ Continent: The extensive stretch of land extent formed by the rocks is called the continent.
→ Plate: Fixed crustal components are called plates.
→ Zone: A zone is an area that has particular features or characteristics.
→ Carboniferous Period: A part of the paleozoic era which was characterized by the process of coal formation. This period was 35 million years ago.
→ Pangaea: In early geologic time, a supercontinent that incorporated almost all the landmasses on the Earth.
→ Panthalassa: Panthalassa means, ‘water only water’. The name given by Wegener to the aquatic counterpart of Pangaea.
→ Geosyncline: A very large trough like depression in the earth’s surface containing masses of sedimentary and volcanic rocks.
→ Angaraland: The northern part of the Pangaea continent described by Wegener, which included Europe, Asia, and North America. It was also called Laurasia.
→ Gondwanaland: The southern part separated from Pangea, which is currently an isolated plot consisting of Africa, Madagascar, Australia, South America, Antarctica and the indigenous parts of Peninsular India, etc.
→ Laurasia: An ancient continental terrain, which was believed to be separated and later from this, Europe, North Asia, North America and Greenland were created. This northern part of Pangea is called Laurasia.
→ Eurasia: Europe and Asia were jointly called Eurasia which was a part of Angaraland.
→ Gravitation force: The attraction force of the earth due to which, all things are attracted to it.
→ Tidal force: The force associated with the attraction of the sun and the moon.
→ Equator: Latitudinal line of zero degree, dividing the earths into the Northern and the Southern Hemispheres.
→ Jig-saw-fit: Status of re-integrative profile of space segments divided by continent in continental drift theory by Wagener.
→ Gulf or Bay: A deep inlet of the sea almost surrounded by land with a narrow mouth or a very large area of sea surrounded on three sides by a coast.
→ Fold Mountain: Fold Mountains are formed as a result of the compression of tectonic plates, which leads to the formation of large fold like structures on the earth’s crust.
→ Sediments: Substances like gravel, sand, punk and lime deposited on the sea bottom, which are transported and deposited by wind, water, glacier or gravity.
→ Glaciation: A microclimatic process or activity under which the icebergs expand on the wide area of the land after the decreases in temperature due to climate change.
→ Fold: Curved twist or tilt in surface rocks caused by their movement due to geothermal force.
→ Reconstruction: The process of re-creation of continents on the crust.
→ Crust: The topmost layer of the Earth on which continents and oceans are formed.
→ Mantle: Around 2900 km thick layer, situated between Crust and Core, whose density is found from 3.1 to 4.75.
→ Lithosphere: Lithosphere is the outermost layer of the earth consisting of the crust and the upper mantle portion of the earth. Lithosphere is responsible for the hard and rigid surface of the earth on which humans exist.
→ Divergence: The process of moving (sliding) in the opposite directions of any two objects is called Divergence.
→ Deeps: The deepest part of the ocean bottom is found in certain areas of the sea bottom, along with the sharply-sloping shield.
→ Ridge: Long and narrow hill with steep slope. Ridge located in the ocean is called inter marine ridge.
→ Continental Plate: Plate associated with continent. The whole or most part of this plate is the land.
→ Ocean Plate: Ocean-related plate. The whole or most part of this plate comes under the ocean bottom.
→ Convergence: When two plates move towards each other from different directions, one of the plates climbs over the other. Such process is called convergence.
→ Transform faults: A special type of fault which determines the separating boundary of two moving plates.
→ Asthenosphere: Below the crust, there is a weak strip in which the rocks are in liquid plastic form. Its surface extends to the depth of 70 – 200 km.
→ Rift Valley: The deep part of the two parallel faults whose width is less but the length is greater.
→ Island festoon Arc: A long, curved chain of oceanic islands. There is often a long and narrow gap in the ocean from the insular arc to the ocean.
→ Geologist: A person who studies the interior of the earth.