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 of the world Before separation After 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 German meterologist 1912 Published 2 articles The Origin of Continents and Oceans Theory of continental drift 1915 proposed hypothesis of continental drift, Supercontinent - Pangea (next slide)

Continental drift hypothesis Figure 15.2 Supercontinent called Pangaea began breaking apart about 200 million years ago Continents "drifted" to present positions Continents "broke" through the ocean crust

Continental drift hypothesis Evidence used by Wegener Wegener 1st scientist look for evidence of continental separation using the Scientific method!

Continental drift hypothesis Evidence used by Wegener Wegener - Observation 1: He 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. - His opponents argued that erosion continually changes shorelines over time.

Continental drift hypothesis Evidence used by Wegener Observation 2: Fossil evidence Several fossil organisms are found on different landmasses in matching locations. Organisms could not have crossed the vast oceans presently separating the continents Example: Mesosaurus Aquatic reptile Fossils limited to eastern South America and southern Africa If the mesosaurs could swim the vast South Atlantic Ocean, the fossils should be more widely distributed

Continental drift hypothesis Evidence used by Wegener Observation 3: Rock types and structures match Appalachian Mountains eastern side of North America continues into Newfoundland Rocks are similar in age and structure in the British Isles and Scandinavia. Landmasses form a nearly continuous belt of matching rock types.

Continental drift hypothesis Evidence used by Wegener Observation 4: 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 More Paleoclimatic evidence Glacial deposits mya Shows ice sheets covered large areas of the Southern Hemisphere 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.

Satellite photo of parallel lakes and mountain ridges

Greenland Glacier