Transcript Continental Drift

T.S.W.B.A.T. understand the dynamic
processes involved in the theory of
plate tectonics.
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2.
What are the layers of the earth
(C.L.A.M.O.I.C) and their state of
matter?
How many cm/year do you think your
fingernails grow?
Continents are moving as we
speak!!!
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South America and Africa are moving
away from each other at a rate of
approximately 2-3 cm/year.
(This is about how fast your fingernails grow)
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The Hawaiian Islands are moving to the
Northwest at a rate of 8-9 cm/year.
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The Earth’s crust is divided into 12 major
plates which are moved in various directions.
This plate motion causes them to collide, pull
apart, or scrape against each other.
Each type of interaction causes a characteristic
set of Earth structures or “tectonic” features.
The word, tectonic, refers to the deformation
of the crust as a consequence of plate
interaction.
World Plates
Continental Drift
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Wegener proposed that
the continents floated
somewhat like icebergs
in water
And that the continents
had drifted apart
He did not know what
caused the continents
to drift apart
His theories were not
widely accepted
Wegener’s Continental Drift
Hypothesis
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Wegener suggested that
225 mya all of the land
masses were connected
in a supercontinent
called Pangaea, a Greek
word meaning ‘all lands’
Continents “Drifted” to
present positions
Continents “Broke” through
Continental Drift
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Alfred Wegener:
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First to Proposed Hypothesis, 1915
Published “The Origin of Continents and
Oceans”
 WHAT
EVIDENCE DID HE USE TO
PROPOSE HIS HYPOTHESIS!!!
Evidence Used by Wegener
1. Fit of South America
and Africa
2. Fossils
3. Ancient Climates
4. Rock Structures
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Alfred Wegener noted that Africa and South America
appear to fit together neatly, like the pieces of a
jigsaw puzzle
He proposed that the continents had been joined and
had since drifted apart
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Fossil remains in continuous bands across
continents
Cynognathus - a land reptile from the Triassic
period
Paleoclimatic
evidence for
Continental Drift
Wegener’s matching of
mountain ranges on
different continents
Main Objection to Continental
Drift Theory
 Its
inability to provide a
mechanism for the
movement of continents.
 How
did the continents
move?
Harry Hess’ Discovery
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During WWII, Harry Hess was a
captain in the Navy on a transport
ship.
His vessel was equipped with an echo
sounder (SONAR or sound waves bounced off
ocean floor). Showed the topography of
ocean floor was NOT flat. which Hess used to
map the ocean floor to aid the war effort
In the postwar period the Atlantic was
extensively mapped and the Mid-Atlantic
Ridge was discovered
Plate Tectonics – Initially
proposed in 1960’s
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More encompassing than continental drift.
Theory that replaced the Continental drift
theory.
Provided a mechanism for movement
Evidence for Plate Tectonics
1. Earthquake and Volcano “Belts”
 Pacific Ring of Fire
2. Ocean Floor Topography
3. Mid Atlantic Ridge
4. Convection Currents
5. Seafloor Spreading
6. Paleomagnetism
Ring of Fire-All around the
Pacific Ocean
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Geologists discovered
that many of the Earth’s
volcanoes and
earthquakes occurred in
a pattern, or set location
Called the Ring of Fire
 Temperature around
the “ring” higher than
in other places
Ocean Floor Has Mountain Ranges larger than
those found on the surface
Mid-Atlantic Ridge
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A giant undersea mountain
range extending north to
south in the center of the
Atlantic Ocean
Ocean sediments were
discovered to be youngest
near the ridge and oldest
near the continental margins
Plate Movement
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“Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
Convection
Sea-Floor Spreading
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Hess’s theory
that new ocean
crust is formed
at mid-ocean
ridges and
destroyed at
subduction zones.
PALEOMAGNETISM – another
piece of evidence supporting
Plate Tectonics
Earths magnetic field will
REVERSE over time. When this
occurs…IRON-BEARING minerals
will arrange themselves parallel to
the Earth’s magnetic bearing.
Essentially, rocks with metal
minerals in them…act like little
compasses…they point to
North…Wherever North is at that
time!!
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Magnetometer – detects small changes in
magnetic fields. Used to construct
“magnetic maps”
The Theory of Plate Tectonics
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a combination of two earlier ideas,
continental drift and sea-floor spreading.
According to the theory, the surface of the
Earth is broken into large plates.
The size and position of these plates change
over time.
The edges of these plates, where they move
against each other, are sites of intense
geologic activity, such as earthquakes,
volcanoes, and mountain building
Map Of The Plate Boundaries