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Chapter 19 Plate Tectonics. Alfred Wegener l A man with an idea. l In 1912 l Noticed similar shapes l similar fossils l Similar rock structures l Similar.

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Presentation on theme: "Chapter 19 Plate Tectonics. Alfred Wegener l A man with an idea. l In 1912 l Noticed similar shapes l similar fossils l Similar rock structures l Similar."— Presentation transcript:

1 Chapter 19 Plate Tectonics

2 Alfred Wegener l A man with an idea. l In 1912 l Noticed similar shapes l similar fossils l Similar rock structures l Similar evidence from glaciers l on continents

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7 Problems With the Theory l Though winds or ocean currents could explain the fossils l Thought the poles moved, so that you could get the glaciers l Didnt explain how it happened. l Though that it was due to the Earth spinning on its axis l Scientists in the southern hemisphere accepted it first l They believed the rocks

8 Solution l Arthur Holmes l Convection currents move the plates.

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10 Ocean-Floor Spreading l In the 1950s and 1960s mapped the ocean floor l Examined underwater mountain ranges l Run for 37,500 miles around the earth. l Found a rift valley in the center l Harry Hess explained – new ocean floor is made at the mid- ocean ridge – Is pushed under other crust at the trenches

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12 Evidence trapped in rocks l Earth is a magnet l When lava cools it keeps track of which way the magnetic pole points. l Every few hundred thousand years the magnetic field switches direction. l Has made stripes of alternating directions on the ocean floor.

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15 Other Evidence l By drilling they have found that rocks near the ridge are youngest, and they get older as you get further away.

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17 Where does it go? l At the edges of the plates one goes under the other l called subduction l It is melted and may make volcanoes. l Evidence comes from earthquakes. l The further you get from the edge, the deeper earthquakes are.

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23 Earthquakes and Volcanoes l Occur in zones around the world

24 Lithospheric Plates l There are 7 major ones,and several others

25 Parts of the lithosphere

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27 Iceland

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29 Convergent Boundary

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35 Convergent Boundaries l Continental and oceanic- ocean subducted, volcanoes on shore l Oceanic and Oceanic- one is subducted, forms an island arc l Continental and continental- folded mountains and a plateau

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37 Boundary types

38 How Fast? l Arctic Ridge 2.5 cm per year l East Pacific rise, off the coast of Chile 15 cm/year l Current movement tracked by satellites

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