is a unifying theme in modern geology that integrates the earlier ideas of

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1 The concept of Global Plate Tectonics is a unifying theme in modern geology that integrates the earlier ideas of continental drift, sea-floor spread, and mountain building To explain why the present ocean floor, which covers only ~71% of earth s surface area, has <200 Ma old rocks, compared to up to ~4.2 Ga old rocks on land, while there is no evidence of any change in earth s surface area during this period.

2 To Alfred Wegener, the evidence of Ma glaciation in today s far flung continents pointed to their having once been joined together and located at the south pole.

3 This is a USGS animation of Wegner s reconstruction of continents made to explain the paleoclimatic evidence.

4 This is a USGS animation of Wegner s reconstruction of continents made to explain the paleoclimatic evidence.

5 Sea floor spread by intermittant volcanism at the mid-ocean ridge (top left) results in the recording by subsequent lavas of the geomagnetic polarity reversals (left bottom) and the resulting marine magnetic anomalies can be mapped by the magnetometers towed by ships (bottom right).

6 How deep sea trenches form Convergence of the continental edges of plates Convergence of continental edge of one plate and the oceanic edge of the other.

7 How folded mountain belts form Convergence of the continental edges of plates Convergence of continental edge of one plate and the oceanic edge of the other.

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9 This is the relief map of the world. If you go to the URL below, you will be able to click on any of the grids here to view enlarged versions of them.

10 The sea floor is not a flat surface

11 Earthquake epicenters display a typically nonrandom distribution

12 Seismicity defines the plate boundaries

13 Some major plates Eurasian North plates American Gorda plate plate Caribbean Philippine plate plate Cocos plate Pacific plate South Nazca American Australian plate plate plate Eurasian plates African plate Indian plate Antarctic plate

14 Age of the sea floor (Ma B.P.) The older the sea floor the farther it is from the ridge axis

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17 The Pacific Ring of Fire

18 North American Plate Boundaries

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23 Continental crust Oceanic crust 0 km 100 km Lithosphere 6371 km 2250 km Inner core Outer core Mantle 200 km 2900 km Mantle Earth is a multi-layered body. This is based on the following evidences: 1. seismic 2. gravity and 3. geomagnetic.

24 A convergent plate boundary, e.g., the convergence of Nazca and South American plates

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30 Juan de Fuca ridge and the associated plates and plate boundaries off the Pacific Northeast and Canada. Note that the Cascadia subduction zone is also called the Filled Trench, as this trench got filled by sediments carried by the huge runoff from land that has characterized this region particularly since the Last Ice Age.

31 Seismicity at the Filled Trench offers the most likely scenario of the western U.S. facing the kind of disaster that the Dec 2004 Asian tsunami, caused by the magnitude 9+ Sumatra earthquake of Dec 26, 2004, wrecked on the Indian Ocean coasts.

32 The Dec 2004 Indian Ocean tsunami was produced by perhaps the strongest earthquake of the past 100 years. It occurred in the Java trench, off Bandar Aceh in northwestern Sunatra. This image is a work of the National Oceanic and Atmospheric Administration

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38 East African Rift valleys and the Red Sea Rift

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40 Models of mantle convection A. Whole-Mantle B. Two-Layer (Ridge) C. Two-Layer (Trench)

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42 Nintyeast Ridge

43 The Hawaii-Emperor seamounts have evolved over the past ~65 Ma as the Pacific plate traversed a fixed mantle plume. (

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