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PPT03 - Drifting Continents

PPT03 - Drifting Continents - Drifting Continents Grand...

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Drifting Continents - Grand Unifying Theories in Earth Science Early Views - The Unchanging Earth “The vast depressions have been ocean basins throughout know history. We may state this unequivocally.” -Baily Willis 1907 Abraham Ortelius: 1596 • Flemish Geographer / Cartographer • “Jig Saw Fit” S-America and Africa Shaking The Tree Leonardo Davinci 1508 • Sea Shells on top of mountains Charles Darwin: 1830’s • Given sediment produced, Why Andes not eroded away? Witness to Earthquake in S-America “Putird muscle shells still adhering to rocks 10feet above high water mark” PROBLEM: Still no mechanism - what caused the earthquakes? The Geosynclinal Theory • First attempt at a “grand unifying theory” Early 1900’s -> 1960’s • Earth cools and wrinkles like an apple • Wrinkles = Mountain Ranges. Essentially a static model - movement in a vertical plane. Problems with the theory: 1. No Mechanism 2. Fails to explain… – A. Jig Saw Fit of continents – B. “lines” of mountains along coast lines – C. Deep ocean troughs off shore – D. distribution of volcanoes and earthquakes – E. Fossil and current biological distribution of life Continental Drift Alfred Wegner , German meteorologist • “Doesn’t the east coast of South America fit exactly the west coast Of Africa as if they had once been joined?…..This is an idea I will have to pursue.” • 1915 “The Origins of Continents and Oceans” proposes continental “drift” Wegner’s Evidence 1. Apparent fit of the continents
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– Ortelius 1596: Americas…... “torn away from Europe and Africa” – 1858 Antonio Snider-Pellegrini, geographer – Today: Fit even better 200m below Sea level 2. “Split Units” • Divide a continent then you divide units that straddle that divide • A. Mountain Belts. Example: Appalachian Mountains - End at NF - “Reappear” in UK and Scandinavia • B. Shield Areas - Example: Saharan Shield Precambrian Rocks
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