1. Chapter 17.1
Plate
Tectonics

2. Plate Tectonics
Overview
Historical Development
Continental Drift and Paleomagnetism

3. 1) Overview-note major plates
TECTONICS
1) Overview-note major plates

4. 1) Overview-note associated volcano and earthquake activity
PLATE
TECTONICS
1) Overview-note associated volcano and earthquake activity

5. PLATE
TECTONICS
1) Overview-note plate interactions that cause volcanoes, earthquakes, & trenches

6. 2) Historical development
PLATE
TECTONICS
2) Historical development
Note how some coastlines fit together like puzzle pieces

7. 2) Historical development
PLATE
TECTONICS
2) Historical development
300 Million years ago Present

8. 2) Historical development
PLATE
TECTONICS
2) Historical development
1915
Alfred Wegener published
hypothesis of
continental drift
He hypothesized:
existence of single
“super-continent”
Pangaea (“pan - G - uh”)
~ 200 million years ago Pangaea broke into
smaller pieces, & “drifted” to present positions

9. P A N G A E A This is what Wegner hypothesized the world to be like
200 million years ago
GONDWANALAND
LAURASIA P A N G A E A

10. Below are maps of the movement Wegner hypothesized

11. 2) Historical development
PLATE
TECTONICS
2) Historical development
Fossil Evidence
Several fossil organisms have been found in common on different continents
-this supports the idea that these organisms lived on connected land masses
Mesosaurus
Lystrosaurus
How can the same species
evolve on widely separated
continents???
Cynognathus
Glossopteris

12. Note the location of identical fossil remains that are on
continents which are now separated by oceans

13. Shown here are more examples of fossil remains and how the
patterns of where they are found match to how the continents
must have previously been arranged

14. More Fossil examples-observe how these support how the continents once fit together

15. 2) Historical development
PLATE
TECTONICS
2) Historical development
Rock evidence
Mountain belts on one continent match up with another.
Similar Mountainous structure and age of rocks:
Appalachians (eastern US)
Matches with
British Isles and Scandanavia

16. Here is how the mountain belt patterns would have formed when the continents were once fit together

17. 2) Historical development
PLATE
TECTONICS
2) Historical development
Rock evidence
Similar rock & mineral deposits are found on different continents – more evidence that the continents were once fit together.

18. 2) Historical development
PLATE
TECTONICS
2) Historical development
Paleoclimate evidence
(ancient)
Ice sheets covered big areas of southern hemisphere
~ million years ago

19. 2) Historical development
PLATE
TECTONICS
2) Historical development
Paleoclimate evidence = fossilized evidence of climate situations
Ice sheets covered big areas of southern hemisphere
~ million years ago – left impressions in rock
Glacial
striations

20. Note where the ice sheet impressions are found and how this is evidence that these continents were once connected

21. 2) Historical development
PLATE
TECTONICS
2) Historical development
1924
Wegener’s book was translated to English – more people read his ideas.
His ideas were met with hostile criticism
Main objection: In addition to some backlash from the religious community about the age of the Earth, Wegner had no way to explain the actual function that caused continental drift.

22. 3) Continental drift and paleomagnetism
PLATE
TECTONICS
Wegener’s idea died until 1950’s.
Renewed interest from rock magnetism
Paleomagnetism: ancient magnetic field of Earth recorded
and frozen into rocks
How?
Need to know about 2 things:
- Earth’s magnetic field
- Magnetism in rocks

23. 3) Continental drift and paleomagnetism
PLATE
TECTONICS
Rock magnetism
-Certain minerals are magnetic (e.g., magnetite, iron)
-They loose magnetization when heated above Curie point (580oC for iron)
-When cooled below Curie pt, magnetic grain aligns w/ Earth’s magnetic field so the direction of the field and the position of the rock where it was found in the Earth can be noted.

24. 3) Continental drift and paleomagnetism
PLATE
TECTONICS
Rock magnetism
-Certain minerals are magnetic (e.g., magnetite, iron)
-They loose magnetization when heated above Curie point (580oC for iron)
-When cooled below Curie pt, magnetic grain aligns w/ Earth’s magnetic field
- It is expected that the rocks will have magnetic alignment as shown below

25. “Polar wandering” 3) Continental drift and paleomagnetism
PLATE
TECTONICS
“Polar wandering”
A discovery in 1950’s showed that some rock formations were not aligned with what was expected.
It was noted that what is the North Pole inferred from rock magnetization appears to have moved in past
The conclusion is that either the North Pole has “wandered” or that the continents have drifted (The ones that were at the North Pole are now moved.)

26. This map shows the curves of polar migration (as per rock magnetic alignment). To overlay these 2 curves, North America needs to be moved uniting it with Europe on the ancient continent of Pangea.

27. Sea floor spreading 3) Continental drift and paleomagnetism
PLATE
TECTONICS
Sea floor spreading
Harry Hess, in the early 1960’s gave a proposal of a means by
which continents could spread:
As per observations of ocean ridges - he proposed these are above mantle upwellings, which cause seafloor to spread, like a conveyor belt
Hess explained that an upwelling of magma replaces the gap in the seafloor as it moves away, becoming new oceanic crust
This is supported by the observation of deep ocean trenches which are locations where oceanic crust has crevasses deep in planet

28. These illustrations show the convection movement of magma as it rises through the gap in the seafloor and pushes the crust outward.

30. 3) Continental drift and paleomagnetism
PLATE
TECTONICS
Geomagnetic reversals are also evidence that magma rises up and pushes the crust outward
Earth’s magnetic field “reverses”
approximately every 400,000 years
The magnetic field is recorded
rocks found in lava flows

31. Seafloor magnetic stripes have been observed and recorded
3) Continental drift and paleomagnetism
PLATE
TECTONICS
Seafloor magnetic stripes have been observed and recorded
1963, Vine & Matthews connected seafloor spreading & continental drift, from magnetic field reversals recorded in cooling lavas of new seafloor
symmetric patterns (“stripes”) on either side of spreading center (mid-ocean ridge)
changes in width of a given stripe indicate changes in spreading rate.

32. This diagram shows the lava flows with the varying magnetic stripes recorded in the rock

33. In Conclusion:
The Theory of Plate Tectonics is now well documented with significant evidence from fossil, mountain, and rock formations
The Theory of Continental Drift is now well documented with significant evidence from sea floor spreading/magma upwellings and magnetic pole recordings in rock formations
Scientists continue to collect evidence to further our understanding of how the surface of the Earth has changed over millions of years.