essential questions what are the lines of evidence that led wegener to suggest that earth’s...
TRANSCRIPT
Essential Questions• What are the lines of evidence that led Wegener to suggest that
Earth’s continents have moved?
• How does evidence of ancient climates support continental drift?
• Why was continental drift not accepted when it was first proposed?
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Ch. 17. Section 1 – Drifting Continents
Review• hypothesis
New• continental drift• Pangaea
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Vocabulary
Drifting Continents
Drifting ContinentsCopyright © McGraw-Hill Education
Early Observations
• With the exception of events such as earthquakes, volcanic eruptions, and landslides, most of Earth’s surface appears to remain relatively unchanged during the course of a human lifetime.
• On the geologic time scale, however, Earth’s surface has changed dramatically.
Drifting ContinentsCopyright © McGraw-Hill Education
Early Observations
• In the late 1500s, Abraham Ortelius, a Dutch cartographer, noticed the apparent fit of continents on either side of the Atlantic Ocean.
• He proposed that North America and South America had been separated from Europe and Africa by earthquakes and floods.
Drifting ContinentsCopyright © McGraw-Hill Education
Early Observations
• The first time that the idea of moving continents was proposed as a scientific hypothesis was in the early 1900s.
• In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community.
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Continental Drift
• Wegener developed a hypothesis that he called continental drift.
• He proposed that Earth’s continents had once been joined in a single landmass, a supercontinent called Pangaea, that broke apart about 200 mya and sent the continents adrift.
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Continental Drift
Evidence from rock formations• Wegener observed that many layers of rocks in the Appalachian
Mountains in the United States were identical to layers of rocks in similar mountains in Greenland and Europe.
• These similar groups of rocks, older than 200 million years, supported Wegener’s idea that the continents had once been joined.
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Continental Drift
Evidence from fossils• Wegener gathered evidence of the existence of Pangaea from
fossils. Similar fossils of animals and plants that once lived on or near land had been found on widely separated continents.
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Continental Drift
Climatic evidence• Fossils of the plant Glossopteris had been found on many parts of
Earth, including South America, Antarctica, and India.
• Wegener reasoned that the area separating these fossils was too large to have had a single climate.
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Continental Drift
Climatic evidence• Wegener argued that because Glossopteris grew in temperate
climates, the places where the fossils had been found had been closer to the equator. This led him to conclude that the rocks containing these fossil ferns had once been joined.
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Continental Drift
Climatic evidence• Coal forms from the compaction
and decomposition of accumulations of ancient swamp plants. Wegener used the existence of coal beds in Antarctica to conclude that Antarctica must have been much closer to the equator sometime in the geologic past.
Copyright © McGraw-Hill Education Drifting Continents
Continental Drift
Climatic evidence• Glacial deposits nearly 300
million years old on several continents led Wegener to propose that these landmasses might have once been joined and covered with ice. The extent of the ice is shown in white.
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A Rejected Notion
• Although Wegener had compiled an impressive collection of data, the hypothesis of continental drift was not accepted by the scientific community.
• Two unanswered questions—what forces could cause the movement and how continents could move through solids—were the main reasons that continental drift was rejected.
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A Rejected Notion
• It was not until the early 1960s, when new technology revealed more evidence about how continents move, that scientists began to reconsider Wegener’s ideas.
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ReviewEssential Questions• What are the lines of evidence that led Wegener to suggest that
Earth’s continents have moved?
• How does evidence of ancient climates support continental drift?
• Why was continental drift not accepted when it was first proposed?
Vocabulary• continental drift • Pangaea
Drifting Continents