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Continental Drift Theory and Plate Tectonic
- 1. Continental Drift Theory and Plate Tectonic
- 2. The Theory of Continental Drift WEGENER 1880 – 1930 Alfred Wegener first proposed the theory of continental drift. Continental drift is the movement of the Earth's continents relative to each other, thus appearing to "drift" across the ocean bed. The continental drift theory is the theory that once all the continents were joined in a super- continent, which scientists call Pangaea.
- 3. Pangaea
- 4. Wegener searched and found three main pieces of evidence Geologic – evidence in the layers of rocks across continents Fossil – evidence in the places certain fossils are found Climate – evidence in the changing climates during the past
- 5. Geologic evidence Rocks of the same age and type and displaying the same formations are found in south- east Brazil and South Africa. The trends of the mountains in the eastern USA and north-west Europe are similar when placed in their old positions. Similar glacial deposits are found in Antarctica, South America and India, now thousands of km apart.
- 7. Climate evidence Climate change evidence Glacial deposits at current equator Fossilized palm trees in Greenland Map shows why according to the placements of current continents within Pangaea
- 9. Theory of Ocean Floor Spreading Scientist once thought ocean floor was solid But because of the great deal of volcanic activity – Lava Lava forms new ocean floor which causes the ocean floor to move or spread out and it will carry the continent with it.
- 10. Theory of Plate Tectonics In the 1960s, scientists developed a new theory that combined continental drift and seafloor spreading . Theory of Plate Tectonics - The theory of plate tectonics, the crust is broken up into sections/pieces that move on top of the liquid mantle (asthenosphere).
- 11. Plates There are 7 major plates on the earth that are moving extremely slowly but continuously. Major Plates: Eurasian, African, Australian-Indian, North American, Pacific, Antarctic and South American. Intermediate Plates: Caribbean, Cocos, Nazca, Arabian, Phillippine, Juan de Fuca and Scotia
- 13. Tectonic Plate Boundaries As scientists’ understanding of mid-ocean ridges and magnetic reversals grew, a theory was formed to explain how tectonic plates move. Plate tectonics theory that explains how large pieces of the Earth’s outermost layer, called tectonic plates, move and change shape. A boundary is a place where tectonic plates touch. All tectonic plates share boundaries with other tectonic plates. The type of boundary depends on how the tectonic plates move relative to one another.
- 14. There are three types of tectonic plate boundaries: 1. Convergent Boundaries 2. Divergent Boundaries 3. Transform Boundaries
- 15. Convergent boundary Two tectonic plates collide What happens at convergent boundaries depends on the kind of crust at the leading edge of each tectonic plate.
- 16. Divergent boundary Two tectonic plates separate New sea floor forms at divergent boundaries. Transform boundary two tectonic plates slide past each other horizontally The San Andreas Fault in California is an example of a transform boundary.
- 17. Possible Causes of Tectonic Plate Motion What causes the motion of tectonic plates? This movement occurs because of changes in the density within the asthenosphere.
- 18. Tracking Tectonic Plate Motion Tectonic plate movements are so slow and gradual that you can’t see or feel them. The movement is measured in centimeters per year. Scientists use a system of satellites called the global positioning system (GPS) to measure the rate of tectonic plate movement.