CONTINENTAL DRIFT AND PLATE TECTONICS.pdf

ELEMENTARY KNOWLEDGE ON Greek, meaning “all lands” or “all the CONTINENTAL DRIFT AND PLATE Earth”). TECTONICS Panthalassa In the early 20th century, a - The ocean that surro...

ELEMENTARY KNOWLEDGE ON Greek, meaning “all lands” or “all the CONTINENTAL DRIFT AND PLATE Earth”). TECTONICS Panthalassa In the early 20th century, a - The ocean that surrounded the scientific theory called continental drift was supercontinent Pangea. (from ancient proposed about this migration of Greek, meaning “all waters”). the continents. That theory was initially ridiculed, but it paved the way for He said around 200 million years ago, the another theory called plate tectonics that Pangaea broke into two, one is Laurasia scientists have now accepted to explain (northern component of the split) and how Earth’s continents move. Gondwana (southern component of the split). The story begins with Alfred Wegener (1880–1930), a German meteorologist and geophysicist who noticed something curious when he looked at a map of the world. Wegener observed that the continents of South America and Africa looked like they would fit together remarkably well—take away the Atlantic Ocean and these two massive landforms would lock neatly together. He also noted that similar fossils were found on continents separated by oceans, additional evidence that perhaps the ALFRED WEGENER COLLECTED landforms had once been joined. He DIVERSE PIECES OF EVIDENCE TO hypothesized that all of the SUPPORT HIS THEORY. modern-day continents had previously been 1. Continents appear to fit together clumped together in a supercontinent he - It has been noted that the coastlines of called Pangaea/Pangea (from ancient South America and West Africa seem to Greek, meaning “all lands” or “all the match up. Earth”). 2. Fossil correlation Over millions of years, Wegener suggested, - The Mesosaurus is known to have been a the continents had drifted apart. He did not type of reptile, similar to the modern know what drove this movement, however. crocodile, which propelled itself through Wegener first presented his idea water with its long hind legs and limber tail. of continental drift in 1912, but it was widely It lived during the early Permian period and ridiculed and soon, mostly, forgotten. its remains are found solely in South Africa Wegener never lived to see and Eastern South America. Now if the his theory accepted—he died at the age of continents were in still their present 50 while on an expedition in Greenland. positions, there is no possibility that the Modern science recognizes this ancient Mesosaurus would have the capability to supercontinent called Pangaea/Pangea did swim across such a large body of ocean as exist before breaking up about 200 million the Atlantic because it was a coastal animal. years ago, as Wegener theorized. This idea also applies to other extinct species such as the Cynognathus, Pangaea/Pangea Lystrosaurus and a tree called Glossopteris. - a supercontinent that incorporated almost all the landmasses on Earth. (from ancient 3. Rocks and geologic structures - Identical rocks and mountain structures Minor tectonic plates are: have been found on either side of the ocean 1. Cocos plate: Between Central which suggests the continents were once America and Pacific plate connected. 2. Nazca plate: Between South America and Pacific plate 4. Past climate data 3. Arabian plate: Mostly the Saudi - Coal deposits have been found in cold Arabian landmass regions and glacial evidence has been 4. Philippine plate: Between the Asiatic found in warm regions. and Pacific plate 5. Caroline plate: Between the The main reason that Wegener's hypothesis Philippine and Indian plate (North of was not accepted was because he New Guinea) suggested no mechanism for moving the 6. Fuji plate: North-east of Australia continents. He thought the force of Earth's 7. Turkish plate spin was sufficient to cause continents to 8. Aegean plate (Mediterranean region) move, but geologists knew that rocks are 9. Caribbean plate too strong for this to be true. So scientists 10. Juan de Fuca plate (between Pacific came up with a new theory called plate and North American plates) tectonics. 11. Iranian plate. Plate Tectonics Tectonic plates - In 1967, McKenzie and Parker suggested - are the different pieces of the Earth's crust the theory of plate tectonics. Morgan later that move around as they float on top of the outlined the theory in 1968. It was from the mantle. continental drift theory, convection current theory and the theory of seafloor spreading, Plate tectonics the theory of Plate Tectonics was - is how those pieces move and interact with formulated. each other. - According to the theory of plate tectonics, the earth’s lithosphere is broken into distinct The part where the plates meet with one plates which are floating on a ductile layer another is called boundaries, there are called asthenosphere (upper part of three types of boundaries: the mantle). 1. Convergent boundary Crustal plates - also called “destructive boundaries” or - The entire earth’s surface is composed of “subduction zones". Occurs when two plates several rigid but relatively thin plates. These are moving towards each other. plates are between 100 and 150 km thick and carry both continental and oceanic crust a. Oceanic – continental convergence with them. They are continuously in motion - The heavier plate usually goes below the with respect to each other. other and may result to building of more pressure and heat making the crust melt The plates vary in size. There are about 20 forming magma. The magma presses up to crustal plates on the earth’s surface, out the surface thus creating volcanoes. An of which seven are very large, these major example of this is the Ring of fire. plates are: (i) the North American plate, (ii) the South American plate, (iii) the Eurasian b. Continental – continental convergence plate, (iv) the African plate, (v) the - occurs when two plates with the same Indian-Australian plate, (vi) the Pacific plate density collide resulting to both of its and (vii) the Antarctic plate. boundaries going upward thus mountain ranges are formed. - An example of this is the Himalayan Mountain Range. 2. Divergent boundary - also called “constructive zones” occurs when two plates are moving away from one another. The space between the two plates widens turning into a huge craft or rift. Example is the east African great rift valley(Continental crust) and Mid-Atlantic ridge(Oceanic crust). 3. Transform boundary - occurs when two plates are sliding pass one another in opposite direction which create cracks or faults. As the plates rub against one another, it builds up pressure. And if the plates are stock for a long period of time, the pressure may build up until it cannot hold any longer then releases it causing earthquakes. Example is the San Andreas fault. Convection Current Hypothesis - Was first suggested by the British geologist A. Holmes in 1927 when he tried to explain the driving mechanism for the continental drift. The high heat flow associated with the oceanic ridges suggests that convention currents exist within the earth. These currents are believed to be responsible for the movement of the crustal plates.