Transcript Continental Drift & Seafloor Spreading

Continental Drift &
Seafloor Spreading
Marine Science
Chapter 11
Continental Drift: What is it?
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Idea that all the continents were once
joined together.
Who came up with the idea?
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Was he the 1st to think of this?
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Alfred Wegener
No
Why did they come up with this idea?
Pangaea
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Theory of Continental Drift
Maps- “puzzle pieces” could make
Super-continent
Wegener called it Pangaea
Ocean called Panthalassa
He thought it might have taken 200 million years
for the continents to split and drift apart to
today’s position
Is there Evidence?
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Maps available in 1600’s pretty accurate
1855 Edward Suess of Germany found
fossils of Glossopteris (ancient fern)
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South America
Africa
Australia
India
Antarctica
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How did they get there?
Too heavy to travel w/wind,
Too fragile to survive sea voyage
Is there more?
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Critters too !!!
Animal fossils found on opposite continents
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Ocean too far for ocean travel
Today we also look to Biogeography
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Like species living on separate continents, but
adaptations have changed do to environmental
conditions
Still more?
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Coal
1908, Ernest Shackleton discovered coal in
Antarctica.
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How is coal formed?
Antarctica MUST have moved
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Coal formed from vegetation being buried in
warm, swampy climates faster than it could
decompose
What is the temperature like in Antarctica today?
Evidences: 3
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Jigsaw puzzle
Fossil remains (both plant and animal)
Coal found in Antarctica
Wegener’s Flaw
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No mechanism for the drift
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Wegener’s theory did not include a strong enough
account for how the continents could move
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No credibility
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He suggested Earth’s rotation & tides moved them
Calculations would prove otherwise
He was a meteorologist, not a geologist
Jigsaw puzzle theory had gaps
He died B-4 theory was accepted
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Disappeared in 1930 in Greenland
Lab
“Dance of the Continents”
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Read as a class
Work in pairs
Turn in when complete
Theory of Seafloor
Spreading
Chapter 11
Meteor- German expedition
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Mid-Ocean Ridges
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Rift Valleys
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Deep valleys running through mid-ocean ridges
Trenches
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Mountain ridges on bottom of ocean
Ravines in seafloor
Patterns were revealed……….
Hess and Deitz- 1960 SFS
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Seafloor is constant state of creation and
destruction
New crust emerges at the mid-ocean ridges
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Magma pushes up through rift and solidifies into
new crust
New sea floor forms at the ridges, and is
then subducted at the trenches (goes back
into the rock cycle)
What are the evidences?
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If this is true, where would you find older
rock; trenches or ridges? Radiometric dating
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If this is true, where is the more dense rock?
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Older is farther away from ridges- trenches
Newer rock will have less deposits on it- more
dense, more layers, older rock is at the trenches
If this is true, magnetism should be
symmetrical
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Huh?
Plate Tectonics combines Continental
Drift and Seafloor Spreading
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P.T. state that Earth has over 12 plates that float
on top of the Asthenosphere
2 different types of plates
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Oceanic; more dense
Continental; less dense
These plates interact in 3 different ways:
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Divergent BoundariesConvergent BoundariesTransform Faults-
So what happens?
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Divergent boundaries- Plates move away
from one another- Constructive Boundaries
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Ridges, valleys, new seafloor; much activity here
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Mtns can form higher than sea level
 Iceland
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Transform (fault) boundaries- Plates slide
past each other- Earthquakes prevalent
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San Andreas Fault in Ca; Pacific/N. American
Plates
Divergent Boundary- Constructive
Transform Fault/Boundary
Cntd Convergent Boundary
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Convergent boundary- 2 plates meet; collisionsDestructive Boundaries
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2 ocean plates; 1 subducts under the other
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Island arcs result
 Japan, Aleutian Islands
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Ocean and continental: more dense oceanic subducts
under less dense continental
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Subduction occurs in trenches
 Range of vocanic mtns: Benioff’s Ring of Fire, Andes Mtns,
Cascades (Mt St Helens)
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2 continental plates: equal densities push mass together
and up
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Himalayans
2 Oceanic Plates
Oceanic meets Continental
Continental meets Continental
Plate Movement
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What is the mechanism behind continental drift?
Convection!
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Warm air rises, then falls as it cools, rises at it warms, etc.
etc.
Convection currents exist w/in mantle; moves plates
away from each other at divergent boundaries, towards
each other at convergent boundaries, past each other at
transform boundaries
Second mechanism is seafloor spreading- plates slide
away from ridges
Lab:
“Dance of the Plates”
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Read as a Class
Work in Pairs
Turn in When Complete
Hot Spots? Activity:
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Grab a Text; w/partner (no more than 2)
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How did volcanoes arise away from plate
boundaries?
Diagram the creation of the Hawaiian Islands
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Explain how it works
 Why is it not one large continent but many islands
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Look at Earth at the following: 225 MYA, 135
MYA, 100 MYA, 65 MYA, and today. Compare
them, and be able to recognize each for test
purposes
Activity:
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Using ONLY your notes, complete the W/S
in class. Due before class is over
Wrap it Up!!
Continental Drift to Plate Tectonics Video
Study Guide Tomorrow
Video Clip
Activity:
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Go over W/S
Create a brochure explaining the way in
which plates move (divergent, convergent,
transform). Be sure to include: Mid ocean
ridge, trench, continental plate, oceanic
plate, rift valley, mid ocean ridge mountain
range.
Exam Tuesday!!! Use W/S as Study Guide
Ring of Fire
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Class Discussions
Research Time
Be sure to complete W/S today
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I will check it off today, we will discuss tomorrow