continental drift. note the shapes south america & africa: they match! what about any others?...
TRANSCRIPT
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Continental Drift
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Note the Shapes South America & Africa: They Match!What about any others? North America?
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Continental Drift:
The Idea that the continents move around and change locations on Earth.
Alfred Wegener proposed the idea of Continental Drift
The globe before and after continental separationBy Antonio Snider-Pellegrini, 1858
(pre-Wegener)
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“Continental Drift” Evidence: Fossils
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“Continental Drift” Evidence: Fossils
• Animal and plant fossils are located on continents that a currently do not touch
• These continents must have touched at some time for matching fossils to be found in the in the areas shown on the continents
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“Continental Drift” Evidence: Glacial Markings
• Marks where glaciers used to scrape along the surface are found on continents that must have once touched
• Some of these continents are in areas currently too warm to support glacier devlopment
• These continents must once have been in colder regions
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“Continental Drift” Evidence: Glacial Markings
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“Continental Drift” Evidence: Mountain Belts
• Mountain belts and rock types connect across continents
• Some matching mountain belts and rock types are found on continents that no longer touch
• These continents must have touched at some time
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“Continental Drift” Evidence: Mountain Belts
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MovingContinents
…Back in time…
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Pangaea
250 million years ago, the continents fit together like a jigsaw puzzle!
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●The Continents Move Around on Earth●Evidence for Continental Drift:
Shape of the ContinentsFossils
Glacial MarkingsMountain Belts
●Pangaea existed when all the continents were together
Conclusions
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Part 1: The Creation of New Oceanic Crust
Seafloor Spreading
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Seafloor Spreading
• Oceanic plates move apart at mid-ocean ridges.
• Magma moves into the rift.• The magma cools and
becomes new ocean floor.• The new material
magnetizes based on the Earth’s magnetic field at the time.
• The new material moves away from the ridge.
• More magma moves into the rift and the cycle continues
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Age and Magnetic Field recorded in the seafloor and spread to each side of the ridge
Each side of the
ridge is the same!!
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Determining Seafloor Age
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●Continents > 4 Billion Years Old●Seafloor < 200 Million Years Old
AGE
continent
ocean
Seafloor Age
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AGE
Age distribution• The colors
represent different ages
• The youngest crust is nearest the ridge
• The pattern is symmetric
• The pattern is more obvious in the Atlantic ocean, where spreading has been very even
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●The ocean is much younger than the continents.
Continents: 4 Billion yearsOceans: <200 Million years
●Seafloor ages make a mirror image (symmetric) pattern.
Conclusions