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Lecture 2

Lecture 2 Historic geology – continental drift & plate tectonics.docx

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University of Toronto Scarborough
Environmental Science
Lisa Tutty

Part of Lecture 2 covered in Lecture 3 Maurice Ewing  Investigated continental shelves and seabed. A continental shelf is the edge of a continent that lies under the ocean. Continents are the seven main divisions of land on Earth. A continental shelf extends from the coastline of a continent to a drop-off point called the shelf break. From the break, the shelf descends toward the deep ocean floor in what is called the continental slope.  explosion seismology, he reflected sound wave to the bottom of the ocean and wanted to know the bottom of the ocean, deposition of sediments, was it tapering off etc  continental shelves have many layers of sediments  the continental shelf is not a permanent feature, but is composed of sedimentary deposits, piled high (up to 3500 m) above the sloping basement of the ocean floor  -the continental shelf is not a permanent feature, but is composed of sedimentary deposits, piled high (up to 3500 m) above the sloping basement of the ocean floor  The deeper the ocean the finer the particles deposited, the reason why continental shelf is not permanent because of the movement of the ocean, the tide and ebb.  In the deeper oceans the clay settles down slowly and gets deposited slowly at the continental shelves.  -if the continental shelf is shallow, larger parts of the continental shelve is exposed.  -think of a river, full of energy and can carry particles of larger size  -he found that the oceanic crust was only 3km thick.  -Continental crust 70-80 km thick  -they did not know about MOR. They did not find any sediment near the MOR. The reason for this is brand new rock, did not have the time for the sediment to settle in.  The further you get away from the MOR the thicker the sediment because with the increase of distance from the MOR the age of crust also increases. The older crust had the time to let the crust settle down. Arthur Holmes:  Famous for geochronology (U-Pb) radiometric dating-gives actual age of rocks. o Many chemical elements in rock exist in a number of slightly different forms, known as isotopes. Certain isotopes are unstable and undergo a process of radioactive decay, slowly and steadily transforming, molecule by molecule, into a different isotope. This rate of decay is constant for a given isotope, and the time it takes for one-half of a particular isotope to decay is its radioactive half-life. For example, about 1.5 percent of a quantity of Uranium 238 will decay to lead every 100 million years. By measuring the ratio of lead to uranium in a rock sample, its age can be determined. Using this technique, called radiometric dating, scientists are able to "see" back in time(just for understanding)  British geologist, supporter of Wegener.  Movement of the continents: result of convection currents driven by the heath of the interior of the Earth, rather than the continents floating on the mantle. Germany had the largest submarine fleet in World War II, since the Treaty of Versailles had limited the surface navy of Germany to six battleships (of less [13] than 10,000 tons each), six cruisers and 12 destroyersPrime Minister Winston Churchill wrote "The only thing that really frightened me during the war was the U-boat peril. After boats designed to look for WWII German U boats or submarines (= undersea boat) mapped the deep sea with new echo sounding tool (German navy boats were banned from harbours) and after the war found continuous mountain like ridge in Atlantic. They also looked for mines that would blow up in the middle of the ocean. -after the war they had all these equipment, so the scientists used them for find the data of the ocean bottom, from one end to the other. -they are mapping bathymetry, the topography under water. First there is the continental shelf then the continental slope, ocean bottom and finally the MOR. The crust at the MOR is buoyant because they are molten and light, and they float. The volcanoes are 2-3km high. They are large volcanoes. Then after the MOR the ocean bottom ends in continental margin of Africa (star*)Marie Thorpe, Cartographer in 1950s (cartographer is someone who can draw maps)  Worked with Maurice Ewing  Echo sounding of ocean floor- detailed map
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