Transcript Life on an Ocean Planet

Alfred Wegener and Pangaea
 Pangaea is the name given to the single giant
continent in a proposal by Wegener (1912).
 The theory of continental drift states that the
continents were once a single landmass that drifted
apart and are still doing so.
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Evidence for Continental Drift
Wegener tried to support his theory
with evidence:
Maps - continents apparently fit together
like a jigsaw-puzzle
Plant and animal fossils - coal in Antarctica
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Evidence for Continental Drift
 Why was his theory not accepted?
No explanation for how drift occurs
He was a meteorologist, not a geologist!
 Plate tectonics theory - explanation for how
continents move, making Wegener’s theory
widely accepted.
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New Technology and Seafloor Knowledge
 Sonar – 1925 first seafloor map of ocean ridges
 New features discovered
 Mid-ocean ridges – mountain ridges on ocean
floor
 Rift valleys – valley in center of MOR
 Trenches
 Scientists observed patterns in features
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Ridges and Trenches
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Seafloor Spreading
 Seafloor constantly being created and destroyed
 New crust at rift valley
 Crust destroyed at trenches
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Evidence for Seafloor Spreading
 Thin sediment in ridges
 Age of rock at ridges much younger than
continents
 Patterns of magnetic polarity reversal
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Seafloor Age
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Types of Movement
 Divergent – plates moving apart (rift valleys in
MOR)
 Convergent – plates coming together
 Transform – plates slide past each other
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Island Arcs
 Convergent ocean plates
 Subduction of denser plate
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Subduction Zones
 Ocean plate into continent
 Trench, mountains, volcanoes formed
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Convergent Continents
 Mountains form
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Hot Spots
 Magma chambers in mantle push through
surface of crust
 Crust moves over mantle forming island
chain
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Plate Movement
 Convection currents form as hot material rises and cold material sinks. This occurs in
the mantle.
 This creates a current that moves the plates away from each other at the divergent
boundaries, toward each other at the convergent boundaries, and past each other at
the transform boundaries.
 A second driving force comes from seafloor spreading.
Chapter 11 Pages 11-26 & 11-27
The Unifying Theory: Plate Tectonics
 Convection is the primary force driving seafloor spreading and
continental drift.
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 As new seafloor forms, the plates
tend to slide away from
the elevated mid-ocean ridges.
Plate Movement (continued)
Chapter 11 Pages 11-28 & 11-29
The Unifying Theory: Plate Tectonics
 Predicted changes over the next 50 million years:
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 The Baja Peninsula will have moved past and apart
from the North American Plate.
 Southern California will pass San Francisco as it
moves to the northwest.
 A new sea will form in eastern Africa.
 Australia will move toward Eurasia/the Equator.
 The Mediterranean Sea will close as Africa pushes
towards Europe.
 The Atlantic and Indian Oceans will continue to grow
while the Pacific will become smaller.