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20_Continental Drift - Chapter 22 Continental Drift and...

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Evidence for continental drift Shapes of landmasses Distribution of ancient fossils Isotopic ages; rock types and structures Apparent polar wander paths Sea-floor spreading magnetic anomalies sea-floor spreading hypothesis sediment thickness and age present-day motions from GPS heat flow and topography Plates boundaries: side and bottom interactions between adjacent plates Divergent boundaries (plates coming apart) East African Rift Chapter 22: Continental Drift and Plate Tectonics Next lecture: Finish chapter 22
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Evidence for continental drift Shapes of landmasses Distribution of ancient fossils Isotopic ages; rock types and structures Apparent polar wander paths Sea-floor spreading magnetic anomalies sea-floor spreading hypothesis sediment thickness and age present-day motions from GPS heat flow and topography Plates boundaries: side and bottom interactions between adjacent plates Divergent boundaries (plates coming apart) East African Rift Chapter 22: Continental Drift and Plate Tectonics Next lecture: Finish chapter 22
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http://pubs.usgs.gov/gip/dynamic/continents.html Ever since navigators started mapping out the Earth’s oceans some have speculated on the oddly good fit between Africa and South America. However, they often went a little overboard in trying to make the fit as close as possible. Here’s an 1858 attempt by geographer Antonio Snider-Pellegrini.
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Alfred Lothar Wegner http://pubs.usgs.gov/gip/dynamic/continents.html Starting in 1912, German meteorologist Alfred Wegener put a lot more intellectual force behind the idea of “continental drift” by considering many types of data beyond just the fit of coastlines.
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www.photolib.noaa.gov One of Wegener’s ideas was to stop fixating on coastlines and instead look at the continental shelves. Good bathymetric data for the seafloor were just beginning to be compiled, as shown in this map from 1915 (where we can already start to see the outlines of the ridge system and the Ring of Fire).
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South America Africa Europe North America When you use the outline of the continental shelf rather than a coastline, the continents on either side of the Atlantic start fitting together much better. There are still a few overlaps, but most of these are “new land” formed by large delta systems dumping sediment into the sea.
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Evidence for continental drift Shapes of landmasses Distribution of ancient fossils Isotopic ages; rock types and structures Apparent polar wander paths Sea-floor spreading magnetic anomalies sea-floor spreading hypothesis sediment thickness and age present-day motions from GPS heat flow and topography Plates boundaries: side and bottom interactions between adjacent plates Divergent boundaries (plates coming apart) East African Rift Chapter 22: Continental Drift and Plate Tectonics Next lecture: Finish chapter 22
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http://www.nhm.ac.uk/nature-online/life/ Lystrosaurus Another of Wegener’s lines of evidence for continental drift arises from fossils of animals and plants that we have good reason to believe would have had a limited geographic range.
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