Chapter 4, Lesson 1, Continental Drift

Chapter 4, Lesson 1, Continental Drift Slide 1 *What is the main idea? ______________ -What are drifting continents? *Despite the evidence that supported continental drift, it was rejected by most scientists. ____________________________________________________ -People who studied maps, about 500 years ago, observed something strange. -They found that the edges of the American continents look as if they might fit into the edges of Europe and Africa.

Chapter 4, Lesson 1, Continental Drift Slide 2 *Who is Alfred Wegener? *Alfred Wegener was a scientist who researched the maps of the continents. *He thought that the edges of the continents might fit together. *In the early 1900s, Wegener proposed a hypothesis(idea) to explain that the continents had once been attached as one huge landmass. *His hypothesis is called continental drift, which is the idea that the continents move very slowly, over millions of years, parallel to the Earth.

Chapter 4, Lesson 1, Continental Drift Slide 3 -What is Pangaea? -Wegener proposed that millions of years ago, the continents formed one huge landmass. -He named this huge supercontinent Pangaea. -According to Wegener, Pangaea started to break apart 200 million years ago. -About 152 million years ago, the Atlantic ocean began to open up between North America and Africa. -About 66 million years ago, India moved toward the Asian continent.

Chapter 4, Lesson 1, Continental Drift Slide 4 *What was Wegener’s evidence for continental drift? *In order to support his continental drift hypothesis Wegener collected data from different scientific fields. *In his book, The Origin of Continents and Oceans, Wegener presented four types of evidence for his hypothesis: Fit of the continents-The most obvious one based on how each of the continents fit together like pieces of a puzzle. Fossil evidence-Wegener collected the fossil evidence of a plant called Glossopteris. He found its seed fossils in South America, Africa, India, and Australia supporting the idea that these continents must have been connected.

Chapter 4, Lesson 1, Continental Drift Slide 5 *What was Wegener’s evidence for continental drift? (continued) 3. Rock types and mountain ranges-Wegener showed that certain types of rocks on the continents would match up if the continents were arranged to form Pangaea. Also, some mountain ranges like the Appalachian Mountains in eastern North America are similar to the mountains in Great Britain and Scandinavia. 4. Ancient climate evidence-Wegener was a meteorologist (a scientist who studies weather). He knew that when sedimentary rocks form, clues about the climate are preserved in the rock. Wegener found that the island of Spitsbergen, east of Greenland had rocks that formed in a tropical (warm or hot) climate.

Chapter 4, Lesson 1, Continental Drift Slide 6 *What was Wegener’s evidence for continental drift? (continued) 4. Wegener suggested that the island drifted from the warm tropics to its current location. He, also, found ancient rocks made by glaciers across Africa, India, and Australia.

Chapter 4, Lesson 1, Continental Drift Slide 7 *What did scientists think of Wegener’s hypothesis? *Wegener presented his evidence for continental drift to other scientists. *He had difficulty explaining how, when, or why the continents slowly drifted across Earth’s surface. *He proposed that the same forces of gravity that produced ocean tides had moved the continents over millions of years. *Most other scientists did not accept this explanation because they could not think of any forces strong enough to make continents drift. *Wegener’s hypothesis was rejected.

Chapter 4, Lesson 1, Continental Drift Slide 8 -What eventually happened to Alfred Wegener? -Alfred Wegener did not give up when his hypothesis was rejected. -However, in 1930, he disappeared and died in a storm while on an expedition studying the weather in Greenland. -He did not live to see the new evidence that made scientists reconsider his hypothesis decades after his death. -Scientists reconsidered Wegener’s hypothesis because of advances in technology, such as sonar and deep sea drilling.

Chapter 4, Lesson 1, Continental Drift Slide 9 *Summary *Alfred Wegener’s continental drift hypothesis is the idea that continents move very slowly across Earth’s surface. *Wegener’s evidence included the geographic fit of the continents, fossils, rocks, and mountain ranges, and ancient climate records. *Wegener presented his hypothesis to scientists who could not think of forces strong enough to make continental drift. *Wegener’s hypothesis was rejected.

Questions??? In the early 1900s, who proposed a hypothesis that explained that the continents were once one huge landmass? What is the idea that the continents move very slowly, over millions of years, parallel to the Earth? What is the name of the huge supercontinent or landmass? What are the names of two pieces of evidence for Wegener’s hypothesis of continental drift? What were the results of Wegener’s hypothesis when he presented it to other scientists?