Transcript Continental Drift & Seafloor Spreading

Continental Drift &
Seafloor Spreading
APES
Chapter 4
Marine Science Style ;)
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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Alfred Wegener
Maps- “puzzle pieces” could make
Super-continent
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Wegener called it Pangaea
Ocean called Panthalassa
Animation
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 (Continental Drift)
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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
Theory of Seafloor
Spreading
Part 2
Meteor- German expedition
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Patterns revealed thru soundings ocean floor
Mid-Ocean Ridges
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Rift Valleys
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Mountain ridges on bottom of ocean
Deep valleys running through mid-ocean ridges
Trenches
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Ravines in seafloor
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-
Marianna’s Trench
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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Type 1: 2 ocean plates; 1 subducts under the other
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Island arcs result
 Japan, Aleutian Islands
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Type 2: 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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Type 3: 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!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
Animation
Lab Day: Computer Time
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Type the websites listed on the lab sheets
Answer the questions
Continue until lab is complete