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Environmental Science
Nick Eyles

EESA06 READING #2 CHAPTER 2 – PLATE TECTONICS What are plate tectonics? Tectonics – the study of the origin and arrangement of the broad structural features of the earth’s surface including folds, faults, mountain belts, continents, and earthquake belts Plate Tectonics – the Earth’s surface is divided into a few large, think plates that move slowly and change in size Plate boundaries – plates move away from one another, past one another, or towards one another Eight large plates/smaller plates – makes up the outer shell of the Earth (the crust and upper part of the mantle) Plate tectonic theory developed by: Continental drift – continents move freely over the Earth’s surface, changing their positions relative to one another Sea floor spreading – A hypothesis that the sea floor forms at the crest of mid-oceanic ridges, then moves horizontally away from the ridge crest toward an oceanic trench. – Two sides of the ridge are moving in opposite directions How did plate tectonics theory evolve? The Early Case for Continental Drift Alfred Wegener • Meteorologist • Continental drift • Examined continents that have identical late Paleozoic rocks and fossils Pangea – continents form a giant supercontinent  Laurasia –northern supercontinent (North America)  Gondwanaland – southern supercontinent Paleoclimatology – study of ancient climate – Examined ancient sedimentary rocks he discovered that paleoclimatic reconstructions suggested polar positions very different to those at present Skepticism about Continental Drift – Believes that the less dense continents drifted through oceanic crust, crumpling up mountain ranges on their leading edges as they pushed against the oceanic crust (DIAGRAM PAGE 25) Renewed Interest in Continental Drift – Study of the Sea Floor o Samples of rocks and sediments can be taken from the sea floor by: 1. Rock Dredge – open steel container dragged over the ocean bottom at the end of a cable 2. Corer – a weighted steel pipe dropped vertically into the mud and sand of the ocean floor 3. Sea-floor drilling – drilling a hole in the deep sea floor o Submersibles – small research submarines for geologists o Single-bean echo sounder – measures water depth and draws profiles of submarine topography 1. A sound is sent downward from the ship and bounces off the sea floor and returns to the ship 2. Water depth = amount of time interval o Sidescan sonar – measures the intensity of sound reflected
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