Plate Tectonics

Plate TectonicsThe 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


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.

MesosaurusAn 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..


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.


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!


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 TectonicsSEA 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


TRANSFORM BOUNDARY - where two plates slide past each other without creating or destroying crust.

Result - Earthquakes

EX: San Andreas Fault (California)


Plate Tectonics

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