Aim : What is the Evidence that supports the idea of Continental Drift?
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Transcript of Aim : What is the Evidence that supports the idea of Continental Drift?
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An Idea Before Its Time
AIM: WHAT IS THE EVIDENCE THAT SUPPORTS THE IDEA OF CONTINENTAL DRIFT?
Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent.
• Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
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EVIDENCE IN SUPPORT OF CONTINENTAL DRIFT1. Continental Drift - continents fit
together like a puzzle2. Matching Fossils - Matching fossils
from different locations that were once together in the past
3. Matching Rock Types - Matching rocks from different locations that were once together in the past
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Zones on Present-Day Continents with Evidence of Glaciation from Pangaean Times
300 M years ago
Present
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BREAK UP OF PANGAEA
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An Idea Before Its Time
CONTINENTAL DRIFT
Evidence• The Continental Fit (Puzzle)• Matching Fossils
- Fossil evidence for continental drift includes several fossil organisms found on different landmasses.
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Fossils of now-extinct animal species in land areas now separated by oceans provide evidence of continental drift.
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An Idea Before Its Time
CONTINENTAL DRIFT
Evidence
• Ancient Climates
• Rock Types and Structures- Rock evidence for continental drift
exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean.
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MATCHING MOUNTAIN RANGES
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GLACIER EVIDENCE
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Rejecting the Hypothesis
CONTINENTAL DRIFT
A New Theory Emerges
Wegener could not provide an explanation of exactly what made the continents move. New technology lead to findings which then lead to a new theory called plate tectonics.
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ESSENTIAL QUESTION: WHAT EVIDENCE DO WE HAVE FOR THE THEORY OF PLATE TECTONICS?
According to the plate tectonics theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer. This layer is known as the lithosphere.
• A plate is one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere.
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Diagram of Lithospheric Plates and Their Interactions
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Evidence for Plate Tectonics
9.4 TESTING PLATE TECTONICS
Paleomagnetism is the natural remnant magnetism in rock bodies; this permanent magnetization acquired by rock can be used to determine the location of the magnetic poles at the time the rock became magnetized.
• Normal polarity—when rocks show the same magnetism as the present magnetism field
• Reverse polarity—when rocks show the opposite magnetism as the present magnetism field
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SPREADING CENTER
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EVIDENCE FOR PLATE TECTONICS4. Glacial Evidence - evidence of past
existence of glaciers in locations that are now warm.
5. Seafloor Spreading – Addition of new oceanic crust at the mid ocean ridges
6. Paleomagnetism – fossil evidence of magnetic pole reversals are evidence of sea floor movement
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EVIDENCE FOR PLATE TECTONICS7. Hot Spots – Hawaiian volcano chain
shows plates moving over hot spot (magma).
8. Earthquakes and Volcanoes – most active earthquakes and volcanoes are located at plate boundaries.
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PALEOMAGNETISM PRESERVED IN LAVA FLOWS
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EVIDENCE FOR PLATE TECTONICS
The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.
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POLARITY OF THE OCEAN CRUST
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Evidence for Plate Tectonics
TESTING PLATE TECTONICS
Ocean Drilling
• The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted.
• The youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.
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Evidence for Plate Tectonics
TESTING PLATE TECTONICS
Hot Spots
• A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands.
• Hot spot evidence supports that the plates move over the Earth’s surface.
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The Big Picture
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HOT SPOT
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Evidence for Plate Tectonics
TESTING PLATE TECTONICS
Earthquake Patterns• Scientists found a close link between
deep-focus earthquakes and ocean trenches.
• The absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.