1. Plate Tectonics

2. Continental Drift Theory
German meteorologist, Some truly revolutionary scientific theories may take years or decades to win general acceptance among scientists. This is certainly true of plate tectonics, one of the most important and far-ranging geological theories of all time; when first proposed, it was ridiculed, but steadily accumulating evidence finally prompted its acceptance, with immense consequences for geology, geophysics, oceanography, and paleontology. And the man who first proposed this theory was a brilliant interdisciplinary scientist, Alfred Wegener.
Born on November 1, 1880, Alfred Lothar Wegener earned a Ph.D in astronomy from the University of Berlin in However, he had always been interested in geophysics, and also became fascinated with the developing fields of meteorology and climatology. During his life, Wegener made several key contributions to meteorology: he pioneered the use of balloons to track air circulation, and wrote a textbook that became standard throughout Germany. In 1906 Wegener joined an expedition to Greenland to study polar air circulation. Returning, he accepted a post as tutor at the University of Marburg, taking time to visit Greenland again in (The above photograph of Wegener was taken during this expedition). In 1914 he was drafted into the German army, but was released from combat duty after being wounded, and served out the war in the Army weather forecasting service. After the war, Wegener returned to Marburg, but became frustrated with the obstacles to advancement placed in his way; in 1924 he accepted a specially created professorship in meteorology and geophysics at the University of Graz, in Austria. Wegener made what was to be his last expedition to Greenland in While returning from a rescue expedition that brought food to a party of his colleagues camped in the middle of the Greenland icecap, he died, a day or two after his fiftieth birthday.
While at Marburg, in the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals found on opposite sides of the Atlantic. Intrigued by this information, Wegener began to look for, and find, more cases of similar organisms separated by great oceans. Orthodox science at the time explained such cases by postulating that land bridges, now sunken, had once connected far-flung continents. But Wegener noticed the close fit between the coastlines of Africa and South America. Might the similarities among organisms be due, not to land bridges, but to the continents having been joined together at one time? As he later wrote: "A conviction of the fundamental soundness of the idea took root in my mind."
Such an insight, to be accepted, would require large amounts of supporting evidence. Wegener found that large-scale geological features on separated continents often matched very closely when the continents were brought together. For example, the Appalachian mountains of eastern North America matched with the Scottish Highlands, and the distinctive rock strata of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil. Wegener also found that the fossils found in a certain place often indicated a climate utterly different from the climate of today: for example, fossils of tropical plants, such as ferns and cycads, are found today on the Arctic island of Spitsbergen. All of these facts supported Wegener's theory of "continental drift." In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener's theory, was published; expanded editions were published in 1920, 1922, and About 300 million years ago, claimed Wegener, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or split, and its pieces had been moving away from each other ever since. Wegener was not the first to suggest that the continents had once been connected, but he was the first to present extensive evidence from several fields.
polar explorer, astronomer, and geologist
In 1912 he proposed Continental Drift Theory
Wegner suggested that all the earth’s land has once been joined into a supercontinent called Pangae
Wegener eventually proposed a mechanism for continental drift that focused on his assertion that the rotation of the earth created a centrifugal force towards the equator.  He believed that Pangaea originated near the south pole and that the centrifugal force of the planet caused the protocontinent to break apart and the resultant continents to drift towards the equator.  He called this the "pole-fleeing force".  This idea was quickly rejected by the scientific community primarily because the actual forces generated by the rotation of the earth were calculated to be insufficient to move continents.  Wegener also tried to explain the westward drift of the Americas by invoking the gravitational forces of the sun and the moon, this idea was also quickly rejected.  Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories
Alfred Wegener
Proposed Theory of Continental Drift (1915)
Failed to provide a mechanism

3. Evidence for continental drift
Jigsaw Puzzle
Evidence for continental drift
Matching coastlines on different continents
Puzzle noted by Leonardo DaVinci and others

4. Evidence for continental drift
Similar Geology
Evidence for continental drift
Matching mountain ranges across oceans
Today
300 million years ago

5. Evidence for continental drift
Glacial ages and climate evidence

6. Fossil Evidence

7. Fossil Evidence
Distribution of fossils such as Mesosaurus
Mesosaurus

8. Permian 225 mya Triassic 200 mya Jurassic 135 mya Cretaceous 65 mya
Breakup of Pangae 225 mya
Present Day

9. Midocean Ridge (Atlantic to Pacific)
New seafloor development at mid ocean ridge
Spreading center
Does this mean that the earth is constantly expanding? No, there are subduction zones
2 football teams: mountain building and trench formation

12. Lithosphere (hard) Asthenosphere (soft) Mesosphere
Lithosphere includes:
Crust– oceanic (basalt)- heavier and thinner
- continental (granite)- lighter and thicker
Lithosphere and asthenosphere differ both physically and chemically
Asthenosphere (soft)
Mesosphere

13. lithosphere
asthenosphere
mesosphere

15. Principles of plate tectonics
The Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another
Plates interact with each other along their plate boundaries
Plate boundaries associated with tectonic activity (mountain building, earthquakes, active volcanoes)

16. Marie Tharp's "World Ocean Floor Map”
1977

17. Evidence for plate tectonics
Pattern of worldwide earthquakes

18. Earthquakes

19. Earthquakes & Plate Boundaries

20. Volcanoes & Plate Boundaries
A circle of volcanic geological activity surrounding much of the Pacific Ocean
volcanoes and earthquake zones coincide
Theory of Plate Tectonics proposed by Tuzo Wilson (1965)
Earth’s outer layer consists of dozens of plates
Plate movement- ave. 5cm/year

21. The 3 types of plate boundaries
Divergent
Convergent
Transform

22. Three Basic Types of Plate Boundaries
Using hands to show relative motion
Divergent
Transform
Convergent
Video: Plate Boundaries— Plates can have three kinds of motion across boundaries: [note video lecture on next slide]
They can move away from each other like at a divergent boundary (= spreading ocean ridge or a rift zone). Or use parallel hands like the transform beginning hands and move them apart allowing the magma (thumbs) to come up.
2. They can move toward each other to make a convergent boundary.
3. They can slide past each other horizontally at a transform boundary.
When two plates carrying continents converge, a continental collision occurs where continental crust piles up. Continental crust is lower density than mantle rocks, so continental rocks cannot be “subducted” into the mantle. If continental rocks are pushed into the mantle, they will soon pop up again. This is like trying to push a piece of styrofoam into a swimming pool. You can push the styrofoam into the water (with some force) but, when you let it go, it pops back to the surface because it is much less dense than the water on which it floats.
ACTIVITY: Teaching about Plate Tectonics Using Foam Models: Download FoamFaultModel_Activity.pdf from Animations Page:
Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication.
You can find this at .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes;
USGS Graphics

23. Three Basic Types of Plate Boundaries
Divergent
Transform
Convergent
Animations: Divergent and Convergent Plate Boundaries
Video lecture by Dr. Robert Butler:Types of Boundaries.mov on the site
Plates can have three kinds of motion across boundaries [more details on next slides]: 1. They can move away from each other like at a divergent boundary (= spreading ocean ridge or a rift zone);
2. They can move toward each other to make a convergent boundary.
3. They can slide past each other horizontally at a transform boundary.
Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication.
You can find this at .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes;
USGS Graphics

24. Divergent plate boundaries

25. Divergent plate boundaries

26. Convergent plate boundaries
a. Ocean-continent
c. Continent-continent
b. Ocean-ocean

27. Convergent plate boundaries

28. Transform plate boundaries
Transform plate boundaries occur between segments of the mid-ocean ridge

30. PLATE POSITIONS: LATE PERMIAN 255 MYA

31. PLATE POSITIONS: LATE JURASSIC 152 MYA

32. PLATE POSITIONS; LATE CRETACEOUS 94 MYA

33. PLATE POSITIONS: MIOCENE 14 MYA

34. PLATE POSITIONS: LAST GLACIAL MAXIMUM 18,000 YA

35. PLATE POSITIONS: MODERN WORLD

36. FUTURE WORLD: + 50 MY

37. FUTURE WORLD: MY