Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 4, 15, 16, 19; Appendix A & B Unit: 4The Forces Within Earth

2. Unit 4: Topic 2.1 Evolution of the Plate Tectonic Theory Focus on . . . • describing the evolution of the plate tectonic theory through the contributions of various scientists.

3. Early Ideas of Crustal Movement • In the early – mid 1900’s, geologists thought that the ocean basins and continents were fixed. During the past 70 years these ideas have brought about a scientific revolution in which new evidence and data support a slowly but continually moving planet. • It was not until 1968 that a theory called “Plate Tectonics”provided reliable evidence supporting a mobile Earth. Text Reference: Chapter 19

4. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • F. B. Taylor • In 1910, he published an article explaining the formation of the Himalayan mountains by moving continents. His ideas were not accepted because he failed to provide supporting evidence.

5. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 2) Alfred Wegener • In 1915, Wegener rattled the scientific community again when he published articles concerning continental drift. • He suggested a super continent called Pangaea existed approximately 200 million years ago and since gradually split apart. (evidence was given, but no mechanism provided to support his ideas).

6. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 3) Arthur Holmes • In 1950’s, he discovered the mechanism to explain why Earth’s lithosphere can move, this was referred to as “convection currents” in the upper mantle (asthenosphere).

7. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • Alexander DuToit • In 1937, he mapped the fit of the continents more accurately by using the continental margins (shelves) instead of the coastlines. This is best seen by viewing Africa and South America.

8. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 5) Harry Hess and Robert Deitz • In the 1960’s, these two scientist proposed the “Sea Floor Spreading”hypothesis and suggested that the sea-floor can be no older than 200 million years.

9. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 6) Frederick Vine and Drummond Mathews • In 1963, these two scientist studied the ocean floor and found that the magnetism in the rocks appear to change (reverse) as you move away from oceanic ridges. • This idea was called “magnetic reversals” and is known to support the idea of Sea Floor Spreading (plate tectonics theory).

10. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 7) J. Tuzo Wilson • Was a Canadian geologist who proposed the existence of “plates” on Earth’s surface as a result of mapping the world’s volcanoes and earthquakes. He put forth the idea that, “Earth consisted of several fragments called plates, instead of being made up of one rigid, solid layer”. This revolutionized the way scientist think of Earth today. • He also proposed the existence of transform faults along plate boundaries; and that stationary hotspots in Earth’s mantle caused volcanism within plates.

11. Early Ideas of Plate Tectonics • Important people of the past and the contribution they made to support a moving Earth (Plate Tectonics). • 8) Xavier Le Pichon and Dan McKenzie • McKenzie published the first paper on the principles of plate tectonics • Le Pichonwas the first to demonstrate on computer the motion of six tectonic plates. He demonstrated that the total crust created at the ocean ridges equaled the amount of crust lost due to subduction at oceanic trenches.

12. Example 1: Which Canadian scientist was responsible for the theory of plate tectonics? (A) Alfred Wegener (B) Robert Deitz (C) Harry Hess (D) Tuzo Wilson

13. Example 2: Which scientists contributed to Plate Tectonics Theory through their work on magnetic reversals? (A) Hess and DuToit (B) McKenzie and Lepichon (C) Vine and Matthews (D) Wegener and Wilson

14. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Which scientists contributed to Plate TectonicsTheory through their work on seafloor spreading? (A) Hess and Deitz (B) McKenzie and Lepichon (C) Vine and Matthews (D) Wegener and Wilson

15. Solutions . . . Questions: Which scientists contributed to Plate TectonicsTheory through their work on seafloor spreading? (A) Hess and Deitz (B) McKenzie and Lepichon (C) Vine and Matthews (D) Wegener and Wilson

16. Summary . . . Overview of Points covered: Scientist that made significant contributions to the plate tectonic theory in the past include; Frank Taylor Alfred Wegener Alexander DuToit Arthur Holmes Harry Hess and Robert Deitz Fredrick Vine and Drummond Matthews J. Tuzo Wilson Xavier Le Pichon and Dan McKenzie