Plate Tectonics

1. Plate Tectonics What Goes On Beneath Our Feet

2. The Beginning Of Time • The time when the earth was born was called the Precambrian Era. • In this Era All of the continents were joined together in one huge island called Pangea

3. PLATE TECTONICS Major Tectonic Plates of the World

4. In addition to the continents drifting, large blocks of heavier ocean floor are also being pushed about the surface of the earth. • The study of this is known as “Plate Tectonics”. There are about 20 oceanic and continent plates.

5. Earth’s Plates • The pieces of the shell are Earth's tectonic plates (12 major ones) and they float across a layer of soft rock like rafts in a stream, their motions driven by forces generated deep in the Earth.

6. Continental Drift Reversed Through the great expanse of geologic time, this slow movement remakes the surface of Earth, expands and splits continents, and forms and destroys ocean basins. Drift Reversed

7. How Old is The Earth • The age of Earth has been subject to debate. Scientists now use an age of 4.6 billion years. • Catastrophismis the thought that Earth is very young, and events described in the Bible are responsible for the appearance of Earth’s features. • The principle of uniformitarianism was introduced in 1788. This principle states that the forces which shaped the Earth are identical to the forces which are working today.

8. Plate Movement • At their boundaries, the plates spread apart, converge, and slide past one another. • These boundaries are the most geologically active regions on Earth.

9. Overview • Here, new land (crust) is born and old land is consumed. • Hot springs spew out mineral-rich waters, volcanoes erupt, and earthquakes tremble -- resulting in devastating tsunamis, floods, and mudslides.

10. Alfred Wegener 1880 – 1930 • In 1910, Wegener noticed the matching coastlines of the Atlantic continents -- they looked on maps like they had once been fit together. • He first spoke on the topic in January of 1912, where he put forth the idea of "continental displacement" or what later was called continental drift.

11. Harry Hess1906-1969 • Harry Hess proved Wegener's basic idea correct and clarifed the mechanism that broke the once-joined continents into the seven continents which we are now familiar with. • The continents are attached to the plates and do not move independently of them. But the plates themselves shift and change shape, carrying the continents along. • In 1960 he hypothesized that the seafloor was spreading from vents in the Rift, where hot magma oozed up.

12. John Tuzo Wilson1908 - 1993 • During the 1960's he refined and championed the theory of plate tectonics, which was then held in disrepute • Introduced the idea of "hot spots" which remain stationary under the moving plates and produce chains of islands like Hawaii and Japan • First to identify "transform faults" which link trenches (where the plates collide) and rifts (where the plates pull apart)

13. Plate Movement • When the heat cells in the center of the earth begin to move in a circular motion due to convection the plates that sit on top of the magma begin to move. • Because magma is molten rock it doesn’t move very fast so the moving of plates takes a very long time

14. PLATE TECTONICS • Convection currents in the mantle rise beneath the Mid-Atlantic Ridge and spread laterally along the base of the plates. • The rocks flow back down into the mantle beneath subduction zones. • Magma is present at very shallow depths immediately beneath the Mid-Atlantic Ridge, not at deeper levels in the convecting mantle.

15. Divergent - Convergent • The plates move apart, away from the mid-ocean ridges (Divergent). • The new crust eventually cools, and over time it is pushed to the side by still more melted rock rising up from within the Earth, in a continuous process (Convergent).

16. Plate Boundaries The lithospheric plates interact with the neighboring plates in several ways. Divergent plate boundaries – Boundaries between plates moving apart, further classified as: Divergent oceanic crust – for example, the Mid-Atlantic Ridge Divergent continental crust - for example, the Rift Valley of East Africa. Extension of divergent boundaries causes splitting and rifting.

17. Plate Boundaries • Convergent Plate Boundaries - Regions where plates are pushing together can be further classified as: • Oceanic crust toward continental crust- for example, the west coast of South America • Oceanic crust toward oceanic crust- occurring in the northern Pacific • Continental crust toward continental crust – one example is the Himalayas Compression at convergent boundaries produces buckling and shortening. Compression

18. Mountains Mountains are formed when two plates collide into each other and cause the land to crinkle and fold.

19. Plate Boundaries • Transform plate boundaries- locations where crustal plates move past one another, for example, the San Andreas fault. Translation at transform boundaries causes shear.

20. Transform plate boundary: plates slide past each other. • The San Andreas fault in California is an example of a transform plate boundary, where the Pacific Plate slides past the North American Plate.

21. Tectonic Formations • Some formations that are formed by plate tectonics are: mountains, ridges, valleys, trenches, volcanoes.

22. Ridges – Volcanic Mountains • Ridges are formed when the pulling apart of a fault in the ocean floor causes magma or “lava” to ooze through and form a bump on the ocean floor. • Over time these bumps turn into a formation like the woops on a dirt bike track, accept its on the bottom of the ocean floor.

23. Ridge System

24. Valleys • Valleys are formed when two plates, continential or oceanic, collide together if the land isn’t pushed upward it gets pushed down and forms a valley.

25. Trenches – Undersea Valley • Trenches are formed when two plates push toward each other and there is a valley in between the plates.

26. Eventually, after more than 150 million years, the cold crust is carried to subduction zones (places where one plate sinks beneath another), where it sinks back into the Earth -- dipping beneath another oceanic plate, or beneath a continent -- and melts once more.

27. PLATE TECTONICS • The North American and the Eurasian Plates are made of rigid mantle and oceanic and continental crust. • The Mid-Atlantic Ridge is the boundary between the two plates. New oceanic crust is created at the ridge. • The Mid-Atlantic Ridge is an example of a divergent plate boundary. Because the plates are diverging, the distance between North America and Europe is increasing.

29. Volcanoes • Volcanoes are formed when magma makes its way to the surface, accumulates a mountain as it cools and then is a giant mountain of cold magma.

30. RINGOFFIRE • Subduction zones, like the so-called Ring of Fire that surrounds the basin of the Pacific Ocean, are among the most violent on Earth.

31. RING OF FIRE • The scraping of one plate on another generates powerful earthquakes; the heating of the plate within the depths of the mantle releases fluids which melt the rock over it, producing molten rock (magma) that surface as volcanoes.

32. EARTHQUAKES – Transform Faults • Earthquakes, too, can occur outside of the plate boundaries. • Within the interior of a plate, stresses -- from buckling, stretching, or compression of the rock -- can build up, until the rock finally breaks crating an Earthquake.

33. The End Directed by: Phyllis Butler