Plate Tectonics The Shifting Earth

Alfred Wegener ( ) German meteorologist Introduced two important ideas PANGAEA - a supercontinent which began to break up 200 MYA CONTINENTAL DRIFT - as supercontinent broke up it formed smaller continents that drifted apart. Wrote a book about his ideas in “The Origin of Continents & Oceans”

Wegener’s ideas were not well-liked.

Evidence for Plate Tectonics The Fit of the Continents

Evidence for Plate Tectonics Fossils

Lystrosaurus “Shovel lizard” - a 200-lb, 3 ft. long mammal-like reptile that had two tusks and looked like a little hippo. Lived about 250 MYA - its remains have been found in Africa, India, Europe, Asia and Antarctica.

Mesosaurus An aquatic reptile which lived about 275 MYA. Fossil remains are found in Africa & South America. If it could swim across the ocean it should be found everywhere... IT ISN’T!

Glossopteris The dominant tree of the southern hemisphere during the early Triassic (250 MYA). Fossil ferns with seeds too big to blow across an ocean have been found in Africa, South America, India, Australia and Antarctica..

Evidence for Plate Tectonics MARSUPIALS - were once the dominant land animal. Were found on every continent. Marsupials are now found only on Australia, while their descendants - like the American Opossum - can be found on other continents.

Evidence for Plate Tectonics GEOLOGICAL EVIDENCE Rocks of different regions match. NW Africa & Brazil Appalachians/Newfoundland & Greenland/Northern Europe

PALEOCLIMATIC EVIDENCE The study of ancient climates (Wegener & his father-in-law were meteorologists) Fossil evidence of glacial deposits of the same age in South Africa, South America, India & Australia show these countries were once over the South Pole! Evidence for Plate Tectonics

PALEOMAGNETISM Rocks “remember” the location of magnetic poles at the time of their formation. They indicate the LATITUDE of the rock at the time of formation. Either the POLES WANDERED or PLATES DRIFTED. Evidence for Plate Tectonics

Wegener vs. the World Some scientists called his ideas “a fairy tale” or “utter damned rot”. Wegener was not a geologist. Scientists felt threatened by an “outsider”. Like Darwin, he had NO MECHANISM. He couldn’t explain what drove the whole system. He knew he was right, but he couldn’t show what made it work. It would be some 50 years before Wegener was proven correct.

Mechanism of Plate Tectonics SEA FLOOR SPREADING - mantle convection currents push magma up, which erupts at Mid-Ocean Ridges, spreading sea floor apart. As lava is formed (basalt)it records the magnetic orientation of the Earth.

DIVERGENT BOUNDARY - plates move apart, resulting in upwelling of material from mantle to create new sea floor. Result - volcanoes, volcanic activity Examples - Mid-Ocean Ridges, Red Sea, East African Rift Valley, Mt. Kilimanjaro Mechanism of Plate Tectonics

CONVERGENT BOUNDARY - where plates move together, causing one of the slabs to be subducted (pushed under) beneath an overriding plate. Three types: Ocean-Continental - Subduction Zone Volcanoes. EX: Cascades, Andes Ocean-Ocean - Volcanic Islands Continental-Continental - Folded Mountains EX: Himalayas Mechanism of Plate Tectonics

TRANSFORM BOUNDARY - where two plates slide past each other without creating or destroying crust. Result - Earthquakes EX: San Andreas Fault (California) Mechanism of Plate Tectonics