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Earth Science Plate Tectonics: A Scientific Theory Unfolds from Continental Drift Objectives Review the historical background leading to the Theory of Plate Tectonics Discuss the Continental Drift hypothesis Review evidence supporting the Continental Drift hypothesis Historical Background on the theory of plate tectonics Abraham Ortelius • Dutch map maker, 1596 • Suggested that the Americas were “torn away from Europe and Africa by great floods and earthquakes” • 1st time suggested in written form Historical Background on the theory of plate tectonics Catastrophism • Until the 1700’s most Europeans thought that a biblical flood played a role in shaping the earth’s surface. • Geology was based on the belief that all changes were sudden and caused by a series of catastrophes Historical Background on the theory of plate tectonics James Hutton • Father of modern Geology, 1785 • Doctrine of uniformitarianism • The present is the key to the past • Geologic forces and processes - both gradual and catastrophic Historical Background on the theory of plate tectonics Antonio Pellegrini • Geographer, 1858 • Made two maps • Before (avant la separation) • After (apats la separation) Historical Background on the theory of plate tectonics Eduard Suess • Viennese Geologist, 1880 • Recognized an Atlantic type of margin • Identified by abrupt truncation of former mountain belts • Recognized a pacific type of margin • Identified by parallel mountain ranges, lines of volcanic areas and frequent earthquakes Historical Background on the theory of plate tectonics Alfred Wegener • 32 year old german meterologist, 1912 • Published 2 articles • The Origin of Continents and Oceans • Theory of continental drift • First proposed hypothesis of continental drift, 1915 • Supercontinent - Pangea (next slide) Continental drift hypothesis •Supercontinent called Pangaea began breaking apart about 200 million years ago •Continents "drifted" to present positions •Continents "broke" through the ocean crust Figure 15.2 Continental drift hypothesis Evidence used by Wegener • Wegener •1st scientist to go out an look for evidence of continental separation •Use of the Scientific method Continental drift hypothesis Evidence used by Wegener • Evidence: The Continental Puzzle • Wegener • Noticed the similarity between the coastlines on opposite sides of the South Atlantic Ocean • Thought that the continents might have been joined • He used present-day shorelines to show how the continents fit together. • However, his opponents correctly argued that erosion continually changes shorelines over time. Continental drift hypothesis Evidence used by Wegener • Fossil evidence •Several fossil organisms found on different landmasses •Organisms could not have crossed the vast oceans presently separating the continents Continental drift hypothesis Evidence used by Wegener • Fossil Evidence continued •Example: •Mesosaurus •Aquatic reptile •Fossils limited to eastern South America and southern Africa • If could swim the vast South Atlantic Ocean •Fossils should be more widely distributed •Land bridges? Continental drift hypothesis Evidence used by Wegener Rock types and structures match • • • Appalachian Mountains eastern side of North America into Newfoundland Similar in age and structure in the British Isles and Scandinavia. Landmasses form a nearly continuous belt. Continental drift hypothesis Evidence used by Wegener Ancient climates • The Northern Hemisphere was once tropical • Evidence: •Coal deposits that were formed from tropical plants. •Assumption: •Large change in climate could not have taken place without continental drift •Instead, N. Hempishere nearer equator Continental drift hypothesis Evidence used by Wegener •Paleoclimatic evidence •Glacial deposits 220-300 mya •Ice sheets covered large areas of the Southern Hemisphere. Continental drift hypothesis Evidence used by Wegener •Paleoclimatic evidence •Layers of glacial till •Southern Africa •South America •India •Australia. •Below beds of glacial debris •Scratched and grooved bedrock carved by the ice. •Looked like ice moved from sea onto land. Summary
