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Plate Tectonics
The Shifting Earth
Alfred Wegener (1880-1930)
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 1915 “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
Evidence for Plate Tectonics
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.
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.
Mechanism of Plate Tectonics
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)