GEOL 101 1nd Edition Lecture 24 Outline of Last Lecture I. Secondary HazardsII. Predicting EarthquakesIII. Preparing EarthquakesIV. Earth’s Interior V. Physical LayersVI. Discovering Earth’s InteriorOutline of Current Lecture I. Continental DrifII. Seafloor SpreadingIII. Plate Tectonics Current LectureContinental Drif-Prior to the 20th century, most of geologists believed the position of the Earth’s continents were fixed. -Several scientists however began to notice that continents, particularly Africa and South America appeared as though they “fit” together, like puzzle pieces-In 1915, Alfred Wegener, a German meteorologist proposed his theory of Continental Drif.-Wegener suggested that single super continent called Pangaea during Mesozoic (200 Ma)- Pangaea began to break apart into smaller continents which gradually “drifed” through the oceans to their modern positions- The idea behind Pangaea was well supported by many forms of evidence, but as we will see, the mechanism behind the movement of the continents was very different-Evidences for Pangaea:- Fit of the continents- Fossil materials across continents- Mountain ranges across continents- Paleo-climates (coal bed and glaciers)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Seafloor Spreading Centers -Wegener’s theory of continental drif lacked a definite mechanism for the movement of the continents - Beginning in the late 1940s, a series of discoveries would provide this mechanism-Following WWII, the US Navy invested millions of dollars for oceanographers to explore the seafloor, in order to locate mines and to build a better defense against enemy submarines- Using sonar techniques, researchers were able to get the first images of the ocean floor- It was then that researchers discovered the ocean ridge systems– extensive chains of underwater mountain rangeso Mid-Atlantic ridge-Within the ocean ridge systems it was observed that tensional forces are pulling the ocean crust apart creating rifs- It was also discovered that at the center of the ridges were underwater volcanoes- Collectively, these observations became known as the seafloor spreading hypothesis-Seafloor spreading centers- The ocean ridges are located above zones of upwelling mantle material, which generatesvolcanism (basaltic lava) and new ocean crust.- The new ocean crust, made of basalt, is pushed away from the center of the ridge like a conveyor belt- The older crust gets pushed away as newer and newer crust continues to form at the ridgePlate Tectonics-By the late 1960s, the concepts of continental drif and seafloor spreading had evolved into a much more encompassing theory known as plate tectonics - Plate tectonics involves the lithosphere (crust and uppermost mantel) which behaves as a strong ridged layers- The lithosphere is broken up into pieces called plates.-Notice that most of the plates include an entire continent, plus significant amounts of oceanic crust, as opposed to Wegener’s idea that the continents moved independently-The tectonic plates are in a constant state of motion which is driven by unequal heat distribution within the Earth- Process known as
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