Transcript Continental Drift: The Beginning of Plate Tectonics

Continental Drift:
The Beginning of Plate
Tectonics
Theory of Continental Drift
Continental Drift
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Theory that the continents are drifting
apart and towards each other
Alfred Wegener
Idea that all continents were all pieced
together 245 million years ago
Pangaea = “All Earth”
Continental Drift
Argument for and against
Continental Drift
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Same fossils on
different Continents
Rock formations
Climate conditions
evidence
Glacial grooves on
separated continents
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Species could travel
over “bridges”
Rock cycle occurs
Climate has cycles
Glaciers covered
majority of Earth
Ultimate Question
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How could gigantic continents move?
What natural force could move entire
continents?
An Answer: Sea Floor
Spreading
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Process in which new oceanic
lithosphere is created as older material
is pulled away
Process forces tectonic plates away
from each other
Creates mid-ocean ridges which are
underwater mountain chains
Sea-Floor Spreading
Evidence for Sea-Floor Spreading
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Eruptions of molten material
Magnetic strips in the rock of the ocean
floor
Ages of rock from drill samples
Magnetic Reversals
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Earth’s magnetic poles change place
Mineral grains of molten rock align to
the poles of Earth
Rocks freeze trapping history of
magnetic reversals
Question: ????
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If new crust is being made at mid ocean
ridges and the sea floor is spreading,
then why isn’t the Earth’s surface
getting larger?
Subduction at Plate Boundaries
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Subduction is a process in which the
dense ocean floor sinks back into the
mantle
Occurs at deep-ocean trenches
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Convergent boundaries
Quiz:
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What are the three layers of the Earth
Based on Composition?
What are the 5 layers based on
Structure?
What is Pangaea?
What process showed Continental Drift
is correct?