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Essay Question Outline
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1. Plate Tectonics
2. Continental Drift
3. Subduction
4. Isostasy
5. Sea Floor Spreading
6. Paleomagnetism
Alfred Wegener: The Theory of Plate
Tectonics
a. Continental Drift
• Started: All land was joined into 1 supercontinent called “Pangaea:
• Over Time: Continents drifted apart creating Gondwanaland and Laurasia,
then Laurasia broke apart into North America, Europe and Asia. Then
Gondwanaland broke into Africa, South America, Antarctica and Australia.
Then India collided with Eurasia. Continents continue to drift apart due to
the convection currents in the Earth to where the continents are today.
• Future: The plates will continue to move based on if they are divergent
(away), convergent (towards) or transform (slide) boundaries until the all
come back together with an inland sea in the middle creating Pangaea
Ultima
Alfred Wegener: Evidence
• Animal and Plant Fossil
• Mesosaurus – S. Am and Africa both had
fossils but couldn’t swim in fresh water
so the continents had to be connected
• Landforms Created:
• Himalayan Mountains when India and Eurasia collided
• Fit together like a puzzle
• Coast of South America and Africa
Alfred Wegener: Evidence continued
• Features common to southern continents:
• rock types and ages (Geochronology Map)
• Glaciation of late Paleozoic age
• Convection Currents
• Hot spots don’t move but the islands due
• Subduction Zones
• Seafloor spreading
• Paleomagnetism
• Earth’s Magnetic Field switched
Subduction Zone = Isostasy Happens
• Subduction: Two plates “converge” together. One
plate is forced UNDER the other and into the Mantle.
• Oceanic Plate more Dense so slips under Continent
Plate less dense creating a trench, volcanoes, island
arc
• Trench: An underwater canyon indicating a
subduction zone and convergent plate boundaries.
Isostasy
• The earth’s crust can move up and down as
a result of the interaction of the downward
force of the crust and the upward force of
the mantle. The balance between these
two forces is called isostasy.
• Examples: Boats, rubber ducks, log float in
the water, glaciers/icebergs, Earth’s crust
on the mantle, subduction zones.
Seafloor Spreading
• Sea-floor spreading is the process in which
the ocean floor is extended when two
plates move apart (divergent boundaries)
• Mid Atlantic Ridge
• Tectonic plates move away from each other
making a crack along the ocean floor.
• Molten Rock rushes upward through the
crack and is solidified by the cooler water.
• This process creates new rock and fills in
the crack. (oceanic ridges)
• The ocean floor spreads as a result.
Seafloor Spreading and Subduction Zone
Paleomagnetism- Over time the magnetic poles of
the Earth have reversed.
By studying the minerals within oceanic ridges
geologist have supported the idea of sea-floor
spreading.
Hot Spots
Mantle plumes are areas of hot, upwelling
mantle. A hot spot develops above the
plume. Magma generated by the hot
spot rises through the rigid plates of
the lithosphere and produces active
volcanoes at the Earth's surface. As
oceanic volcanoes move away from the
hot spot, they cool and subside, producing
older islands, atolls, and seamounts. As
continental volcanoes move away from the
hot spot, they cool, subside, and
become extinct.
Hawaii Hot Spots
• Hawaii is the youngest island and it is still being formed today; thus,
Hawaii is currently at the hot spot location.