2. 1. Paleomagnetism

3. ◦ when hot, minerals in newly formed rocks align themselves with the earth’s magnetic poles ◦ As the Earth’s magnetic poles change so do the direction of the rock’s magnetic poles  Therefore: rocks formed millions of years ago show the location of the Earth’s magnetic poles at the time of their formation

4.  strips of alternating polarity - mirrored on each side of ocean ridges  one strip of rock has normal polarity (north pole of the rock faces the north pole of the Earth)  another strip of rock has reversed polarity (north pole of the rock face the south pole of the Earth)  Therefore: Each strip that has a different polarity had to be formed at different time – supports sea floor spreading

6. ◦ A link between deep-focus earthquakes and ocean trenches ◦ Shallow earthquakes occur near or at the trench ◦ Deep earthquakes occur toward the mainland

8. ◦ Drilling of the ocean floor from the mid ocean ridge toward the coast lines ◦ Oldest rocks were found closest to the shoreline, youngest nearest the ridge ◦ Therefore: The ridge is producing new oceanic crust while older crust is being pushed toward the shoreline

9. ◦ Rising magma from the mantle (in the ocean) produces volcanoes along the floor of the ocean ◦ As plates move, new volcanoes are formed along the floor bottom above the hot spot ◦ Chain of underwater volcanoes and islands from the Aleutian trench to Hawaii – age of features increase as you move away from Hawaii ◦ Therefore: The plates are moving over the hot spot and forming new volcanic features. ◦ http://www.youtube.com/watch?v=AhSaE0omw 9o http://www.youtube.com/watch?v=AhSaE0omw 9o http://www.youtube.com/watch?v=bYv6V5EJ AKchttp://www.youtube.com/watch?v=bYv6V5EJ AKc

10.  Convection Currents basic driving force ◦ Hot, less dense magma rises toward the crust while cooler, more dense magma sinks ◦ Plates move because of the uneven distribution of the Earth’s heat

11.  The pulling of old crust down in the mantle because by the downward flow of more dense magma in the convection current

12. The down-ward pull, from gravity, on the oceanic lithosphere at the ridge

13.  http://www.youtube.com/watch?v=ryrXAGY1 dmE http://www.youtube.com/watch?v=ryrXAGY1 dmE