1. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Earth Systems 3209 Unit: 4 The Forces Within Earth Reference: Chapters 4, 15, 16, 19; Appendix A & B

2. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Theory of Continental Drift Unit 4: Topic 1.1 Focus on...  describing the theory of continental drift as proposed by Alfred Wegener.  discussing the ideas provided by both Alfred Wegener and Arthur Holmes explaining the mechanism behind continental movement.

3. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Theory of Continental Drift Some earlier ideas of continental drift include:  Rodinia is one of many different supercontinents that is believed to have existed before Pangaea.  An early theory believed that continents simply ‘drifted’ through the ocean floor pushing up material in front, forming mountain belts. However, this theory lacked a valid mechanism for driving the process behind continental movement.  Many of the earlier theories had trouble explaining the process of why the continents moved ….

4. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Theory of Continental Drift  A German scientist, named Alfred Wegener was one of the first scientist to propose that continents had once been closer together.  Wegener called this idea “Continental Drift.” His idea was not widely accepted because scientist believed that the continents and oceans were permanent features fixed in their position and did not move. Text Reference: Pages 514-515

5. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Wegener’s idea was:  Hundreds of millions of years ago, a supercontinent called, “Pangaea” once existed. At approximately 200 million years ago, this landmass split into smaller pieces and drifted apart reaching their present day positions. Theory of Continental Drift

6. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Wegener’s main criticism centered around why the continents move.  A weakness in Wegener’s theory was it could not satisfactorily answer the question asked by critics: Q: What kind of forces could be strong enough to move such large masses of solid rock over such great distances?  In 1915, Wegener suggested that the continents plow through the oceans as a snow plow would trough snow. He also believed that the Earth’s rotation and the moon’s gravitational forces were responsible for the drifting of continents. This reasoning for the movement of continents was not widely accepted since most scientists still believed the Earth was a solid, motionless body. Theory of Continental Drift

7. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Main Points of Continental Drift Theory Include: 1)225 Million years ago, supercontinent called Pangaea. 2)200 Million years ago, supercontinent split to form two main land masses. Laurasia in the north and Gondwanaland in the south. 3)Laurasia consisted of; Asia, Europe, and North America. 4)Gondwanaland consisted of; Africa, Australia, Antarctica, South America, and India. 5)Over the past 150 million years, these land masses split and drifted to their present positions. Theory of Continental Drift

8. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  After Wegener’s death in 1930, much evidence was discovered to support the Continental Drift Theory.  However, at the time that Wegener proposed his theory of continental drift, most scientists still believed the Earth was a solid, motionless body.  Majority of this evidence was discovered during ocean floor exploration and the question Wegener failed to answer was explained by a scientist named Arthur Holmes.  Holmes speculated that the circular motion of the mantle carried the continents along in much the same way as a conveyor belt. Theory of Continental Drift

9. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Holmes suggested that continents and the ocean floor move primarily due to forces in the asthenosphere (upper mantle) which causes material to move as convection cells.  Mantle material moves up at ridges and move away in opposite directions moving the continents. In cooler areas beneath trenches, mantle material sinks causing oceanic crust to descend into the mantle and be recycled.  This idea was first considered in the 1930s by Arthur Holmes, the English geologist who later influenced Harry Hess' thinking about seafloor spreading. Theory of Continental Drift

10. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 1: Which scientist proposed the existence of a supercontinent called Pangaea? (A)Alfred Wegener(B)Arthur Holmes (C)Harry Hess(D)Tuzo Wilson Which is the name of the supercontinent that existed before Pangaea? (A)Gondwanaland(B)Iapetus (C)Laurasia(D)Rodinia

11. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 2: Which is the most recent supercontinent? (A) Appalachians(B)Iapetus (C)Pangaea(D)Rodinia Which Earth layer contains convection currents that cause plate movement? (A)asthenosphere(B)inner core (C)lithosphere(D)outer core

12. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Your Turn... Take the time and complete the following questions... (Solutions to follow) Question: With reference to Rodinia and Pangea, use the Plate Tectonics theory to describe what our planet could look like in the future.

13. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Solutions... Question: With reference to Rodinia and Pangea, use the Plate Tectonics theory to describe what our planet could look like in the future. Answer: In the past billion years scientist suggest that the major landmasses of Earth joined together on numerous occasions to form super continents, Rodinia and Pangaea are two such examples. With undisputable evidence supporting a mobile Earth which forms the basis of the plate tectonic theory, it is believed that the major landmasses will once again in the future join to form another massive super-continent.

14. Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Summary... Overview of Points covered:  Alfred Wegener proposed the Continental Drift Theory.  Wegener could not explain why the continents move!!  Arthur Holmes proposed an acceptable “mechanism” to explain Wegener's theory of continental drift.  Holmes suggested that the movement of convection currents in the Asthenosphere is responsible for moving the continents.  Holmes ideas behind convection in the mantle later influenced Harry Hess to propose the theory of seafloor spreading.