G10 U1 Article on Continental Drift, Seafloor Spreading, and Plate Tectonics PDF

ASSUMPTION COLLEGE, SLV BASIC EDUCATION DIVISION SY 2024 – 2025 First Quarter...

ASSUMPTION COLLEGE, SLV BASIC EDUCATION DIVISION SY 2024 – 2025 First Quarter SCIENCE and TECHNOLOGY 10 Name: ______________________________________________ Date: __________________ Section: __________________ Theories explaining the distribution of Oceans and Continents: Continental drift, Sea floor spreading & Plate tectonics Lifted from Rau’s IAS Study Circle Earth is dynamic. Forces keep on changing the location of the continents and the oceans. There are various theories which explain the evolution of our planet. Continental Drift Theory Put forward by Alfred Wegner in 1912 Also called the ‘displacement hypothesis’ Wagner believed in a three-layer system; the outer layer of sial, an intermediate layer of sima, and the lower layer of nife. (sial is restricted to continent only and sialic masses float over) According to Wegener, all continents formed a single continental mass (PANGEA) & mega ocean (PANTHALASSA) surrounded the same. Around 200 million years ago, Pangaea first broke into two large continental masses: Laurasia (Present day- N. America, Europe, and Asia) and Gondwanaland (Present day S. America, Africa, Peninsular India, Australia and Antarctica). Subsequently, Laurasia and Gondwanaland continued to break into various smaller continents that exist today. Wegener suggested that the movement responsible for the drifting of the continents was caused by pole-fleeing force (a force that acts on a particle or object causing it to move in a circular pattern) and tidal force (force caused by the sun and moon’s attraction to Earth, which causes tides to form). Pangaea to modern-day continents. Image retrieved from https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ © Copyright August 2024 by Assumption College, Metro Manila, Philippines. All rights reserved. No part of this material/work can be reproduced, copied, and/or distributed without the express permission of the copyright owner. Evidence in Support of Continental Drift Theory Jig Saw Fit Theory: Shorelines of Africa & South America facing each other have a remarkable and unmistakable match and can be refitted together. Rocks of the Same Age Across the Oceans: The belt of ancient rocks from the Brazil coast matches with those in western Africa. The Appalachians of N. America is compatible with the mountain system of Ireland and North-western Europe. The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere. Placer Deposits: Brazil has gold-bearing veins but the gold is also found at the coast of Ghana which has an absolute absence of source rock. Distribution of Fossils: Observations that Lemurs occur in India, Madagascar, and Africa led some to consider a contiguous landmass ‘Lemuria’ linking these three landmasses. The carboniferous glaciation of Brazil, Falkland, South Africa & peninsular India further proves the unification of landmasses during the carboniferous period. Seafloor spreading & Plate tectonic theory also proved that lands and seas are not stationary and they keep on drifting. Evidence of Continental Drift. Image retrieved from https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ Seafloor Spreading Theory Theorized by Prof Harry Hess Mid-oceanic ridges are situated on the rising thermal convection currents coming up from the mantle. Constant eruptions at the crest of oceanic ridges cause the rupture of the oceanic crust and the new lava wedges into it, pushing the oceanic crust on either side. The ocean floor, thus spreads. Molten lava cools down and solidifies to form new crusts along the trailing ends of divergent oceanic crusts. The spreading of one ocean does not cause the shrinking of the other because of the consumption of the oceanic crust at the oceanic trenches. © Copyright August 2024 by Assumption College, Metro Manila, Philippines. All rights reserved. No part of this material/work can be reproduced, copied, and/or distributed without the express permission of the copyright owner.  Mantle convection happening on the earth’s mantle. Image retrieved from https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ Evidence in Support of Seafloor Spreading Rocks equidistant on either side of the crest of mid-oceanic ridges show remarkable similarities in terms of period of formation and chemical composition. Rocks on either side of the mid-oceanic ridge have similar magnetic properties in terms of magnetic anomaly and time sequence of magnetic epochs. The age of rocks increases as one moves away from the crust. Ocean crust rocks are much younger than continental rocks. The age of rocks in the oceanic crust is nowhere more than 200 million years old. Some of the continental rock formations are as old as 3,200 million years. Sediments on the ocean floor are unexpectedly very thin. Plate Tectonics Theory Suggested by McKenzie and Parker in 1967 and outlined by Morgan in 1968 A tectonic plate (also called a lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plates move horizontally over the asthenosphere as rigid units. Forces responsible for such movements - the heat beneath the earth is generated because of two factors: (i) radioactive decay and (ii) residual heat. The lithosphere includes the crust and top mantle with its thickness range varying between 5 and 100 km in oceanic parts and about 200 km in the continental areas. A plate may be referred to as the continental plate or oceanic plate depending on which of the two occupy a larger portion of the plate. Tectonic Plates. Image retrieved from https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ © Copyright August 2024 by Assumption College, Metro Manila, Philippines. All rights reserved. No part of this material/work can be reproduced, copied, and/or distributed without the express permission of the copyright owner. Three Types of Plate Boundaries Divergent: Where new crust is generated (Constructive margins) as plates pull away from each other and new crusts are formed because of solidification of upwelling molten material. These sites are called spreading sites. Ex. Mid-Atlantic Ridge (American Plate(s) being separated from Eurasian and African Plates). Convergent: Where the crust is destroyed (Destructive margins) as one plate dives under another. They are also known as consuming plate margins. The location where sinking of a plate occurs is called a subduction zone. There are three ways in which convergence can occur. (i) Ocean-Ocean convergence (ii) Ocean-Continent convergence (iii) Continent-Continent convergence Transform: Where the crust is neither produced nor destroyed as the plates slide horizontally past each other. They are generally perpendicular to the mid-oceanic ridges. They are formed due to differential movement. Also, the rotation of the earth has its effect on the separated blocks of the plate portions. Plate Motion. Image retrieved from https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ Evidence of Plate Tectonics Evidence of Continental drift, paleomagnetism, and sea floor spreading theory can be combined. Continental drift proves that there has been a motion i.e., ‘tectonics’. Paleomagnetism and seafloor spreading theory explains the process behind this movement. ----------------------------------------------------------------------------------------------------------------------------------------- Reference: Tripathi, G. (2023, May 18). Theories explaining the distribution of Oceans and Continents: Continental drift, Sea floor spreading & Compass by Rau’s IAS. https://compass.rauias.com/geography/oceans-continents-continental-drift-sea-floor-spreading-plate-tectonics/ © Copyright August 2024 by Assumption College, Metro Manila, Philippines. All rights reserved. No part of this material/work can be reproduced, copied, and/or distributed without the express permission of the copyright owner.