Download Continental Drift

Continental Drift
• Alfred Wegener thought of the theory of continental drift-that
the continents move.
• 250 million years ago all the continents were connected as
only one continent called Pangaea.
• His reasons were:
– The same types of rock were on different continents
– The shapes of the continents “fit together”
– The same types of fossils were on different continents
• 180 million years ago Pangaea broke in two pieces,
Gondwanaland and Laurasia
• Geologists think that convection currents in the mantle move
large sections of the Earth’s crust, called plates.
• The plates are still moving!
The Plates of the Earth
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North American Plate
South American Plate
African Plate
Eurasian Plate
Pacific Plate
Indo-Australian Plate
Antarctic Plate
Nazca Plate
Boundaries
• Plates move ___________________________ at transform boundaries.
• Plates move ___________________________ at divergent boundaries.
• Plates move ___________________________ at convergent boundaries.
• Transform Boundaries
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frequently cause ___________
no new crust formed, __________ old crust recycled
moves about 2 in (5 cm) per year on average
example: ________________
• Divergent Boundaries
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plates move _______________each other
examples: the Mid-___________ Ridge, Iceland, the African Rift Valley
lava forms new crust and __________ the older crust away.
underwater this is called sea-floor _____________
the newest crust is _____________________
most ______________ are at divergent boundaries
Boundaries p.2
• Convergent Boundaries
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Plates move towards each other and ________
Examples: Ring of Fire, Andes Mtns., Aleutian Islands, Himalayan Mtns.
many mountains, volcanoes and ___________ happen at convergent boundaries
old crust is ________ and recycled
Could be continent vs. continent
• pushes up tall __________________ parallel to boundary, like Himalayan
Mountains with Mt. Everest
– Could be oceanic vs. (continent or oceanic)
• oceanic plates are ___________ and heavier than continental plates
• subduction occurs when the oceanic plate slides _______________ the other
plate and melts in mantle.
• forms a deep trench, example: _____________ Trench in Pacific Ocean or arcs of
____________________ that are parallel to boundary
• makes lots of cracks in upper plate, which fill with ______________ making
___________________
Earthquakes
• happen at faults (cracks in the crust), not just at transform boundaries
• Faults are in tension (being pulled), until they move and vibrate
• Seismic waves carry those energy from those vibrations in 3 directions
– P waves go front to back, fastest speed
– S waves go side to side
– Surface waves go up and down, slowest speed
• The focus is where the earthquake starts underground.
• The epicenter is directly above the focus on the surface.
• A seismometer is a device that prints a picture of the vibrations called a
seismograph.
• The magnitude (strength) of an earthquake is measured on the Richter
scale.
• NO ONE CAN PREDICT AN EARTHQUAKE!