Ch 17 Section 1 Drifting Continents Essential Questions

Ch. 17. Section 1 – Drifting Continents 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? Copyright © Mc. Graw-Hill Education Drifting Continents

Vocabulary Review New • • • hypothesis Copyright © Mc. Graw-Hill Education continental drift Pangaea Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

Early Observations • In the late 1500 s, 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. Copyright © Mc. Graw-Hill Education Drifting Continents

Early Observations • The first time that the idea of moving continents was proposed as a scientific hypothesis was in the early 1900 s. • In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community. Copyright © Mc. Graw-Hill Education Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

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 Europe. • These similar groups of rocks, older than 200 million years, supported Wegener’s idea that the continents had once been joined. Copyright © Mc. Graw-Hill Education Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

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 © Mc. Graw-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. Copyright © Mc. Graw-Hill Education Drifting Continents

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. Copyright © Mc. Graw-Hill Education Drifting Continents

A Rejected Notion • It was not until the early 1960 s, when new technology revealed more evidence about how continents move, that scientists began to reconsider Wegener’s ideas. Copyright © Mc. Graw-Hill Education Drifting Continents

Review 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? Vocabulary • continental drift Copyright © Mc. Graw-Hill Education • Pangaea Drifting Continents