theory of continental drift continental drift â€¢ the theory of continental drift was proposed...
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Unit Essential Question: How does the Earth recycle and renew its surface?
Presentation Objectives: § Define the theory of continental drift. § Explain the different evidence that supports the theory of continental drift.
What A Dynamic Place! • Even though the Earth seems relatively unchanging,
scientists have evidence that the Earth’s surface actually is changing.
• The continents are moving!
• The Theory of Continental Drift is the theory which proposes that the Earth’s continents had once been joined as one single landmass.
• Known as Pangaea
• Pangaea broke apart about 200 million years ago.
• The continents drifted to their present positions.
• They Fit Together! • Early mapmakers noticed that the continents
looked like they fit together like puzzle pieces.
• Not a perfect fit! • The continents as we see
them do not fit well. • You get a perfect fit when you
consider the continental margins.
• Continental margins are the edges of the continents that are underwater.
Observation 2 • Rock Formations
• Different continents showed the same rock types in exactly the same order.
• These rocks and minerals were not found on the ocean floor between the continents.
Diamonds found indicate areas of high pressure!
• Mountain Ranges • When continents where
connected, the mountain ranges lined up to form one continuous range.
• Ex: Appalachian Mountains
Observation 2 Continued...
When Pangaea broke apart, large geologic formations broke apart.
• Fossils • The remains of different species were found on
widely separated continents.
Mesosaurus Lystrosaurus Glossopteris
If many of the fossils were of land-dwelling animals and plants, then they were unable to swim across the oceans!
• Ancient Climate • Sandstone and coal forms
in warm, rainy climates typical of the equator.
• Found in Canada, Europe, and Antarctica.
• Glaciers form in the cold tundra.
• Glacial rocks are found in India, Africa, Australia, and South America
Observation 4 What A Crazy Idea! • The Theory of Continental Drift was proposed
by a meteorologist named Alfred Wegener.
• Despite the evidence that Wegener collected, the scientific community rejected his hypothesis.
• Wegener could not provide a mechanism that would cause the continents to move in this way.
Wegener died in 1930, still trying to gather evidence to support his theory. The Theory of Continental Drift was accepted as correct in the 1960s.