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Physical Geography Continental Drift / Plate Tectonics Geologic History • The surface of the earth is a thin layer of moving plates that float on the mantle. • Each earthquake is an indication of the movement of the earth’s upper layer called the crust. • Seismologists (scientists who study earthquakes) have discovered that earthquakes occur more frequently in specific areas. • Earthquakes and volcanoes frequently occur where the edges of the earth’s plates are spreading, colliding, or sliding from one another. Types of Plate Behaviour Spreading / Divergent Colliding / Convergent Sliding / Transform The Earth’s Interior A. Crust B. Upper Mantle C. Asthenosphere D. Lower Mantle E. Outer Core F. Inner Core Moho Discontinuity – The dividing line between the asthenosphere and the earth’s crust. Gutenberg Discontinuity – The dividing line between the solid mantle and the liquid core of the earth. Alfred Wegener’s Theory of Continental Drift ① He saw the jigsaw fit between South America and Africa. ② He found fossils of the same plants and animals on different continents. ③ There are mountains similar in age and structure on both sides of the Atlantic Ocean ! the Appalachian Mountains in North America were similar to the Caledonian Mountains in Europe. ④ Glaciers once covered southern Africa, India, Australia and South America. Why did most scientists disagree with Wegener? " Wegener could not explain what mechanism was powerful enough to move huge continents. Alfred Wegener’s Theory of Continental Drift Plate Tectonics • In the 1960’s the idea of continental drift was revived by John Tuzo Wilson (Canadian geophysicist and geologist). • He conducted a detailed analysis of glaciers, mountains and sea beds. " He expanded on Wegener’s ideas by establishing the concept that the continents moved on plates • About 300 million years ago all the earth’s land masses were joined together into one supercontinent called Pangaea • About 200 million years ago Pangaea began to break up, with each tectonic plate moving in a different direction. Plate Behaviour Pangaea Given the currently estimated drift rates and directions of the plates, we can trace their movements back into the past. About 200 million years ago, they would have been at the approximate positions shown in (a). The continents’ current positions are shown in (d) Theory of Plate Tectonics • The earth’s crust is made up of about 20 plates. • These plates are moving over a layer of molten rock known as the mantle. • It is believed that the unequal distribution of heat within the earth causes convection currents to move the plates. Mount Kilauea, Hawaii / Kobe, Japan [A] An active volcano on Mount Kilauea in Hawaii. Kilauea seems to be a virtually ongoing eruption. [B] The aftermath of the earthquake that claimed more than 5000 lives and caused billions of dollars' worth of damage in Kobe, Japan in January 1995. San Andreas Fault The San Andreas and associated faults in California result from the North American and Pacific plates sliding past one another. (a) A small part of the fault line separating the two plates. (b) A satellite photo of the San Francisco Bay area, showing the location of two fault lines. (c) A larger-scale view of the fault system. Evidence of Plate Tectonics ① Coastline Fit – Continents fit together like a jigsaw puzzle. ② Geologic Fit – similar mountains in North America and Europe. ③ Glacial Evidence – Evidence that glacier existed on Africa, Australia, India and South America. ④ Fossil Correlation – Similar fossils of plants and animals found on adjacent continents. Evidence of Plate Tectonics (continued) ⑤ Paleomagnetism – As volcanic rock cools magnetic elements align themselves with the earth’s magnetic field. ⑥ Mid-oceanic Ridge – Rocks are younger closer to the ridge and older as you move further away from it. ⑦ Satellite Measurements – Satellites have detected that the plates are moving 1-2 cm per year. Major Earthquakes and Volcanoes Red dots represent active sites where major volcanoes or earthquakes have occurred in the twentieth century. The sites outline vast "plates" that drift around on the surface of our planet. Earthquakes in Canada Significant Earthquakes in Canada