Understanding Planet Earth Final Review - Understanding Planet Earth Final Review Question 1 Paleomagnetism and Geomagnetic Pole Paths Paleomagnetism

Understanding Planet Earth Final Review - Understanding...

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Understanding Planet Earth Final Review Question 1: Paleomagnetism and Geomagnetic Pole Paths Paleomagnetism – study of earths magnetic fields in rocks o When Igneous rocks (lava flows) form they become weakly magnetized as they cool. Direction of magnetism preserves a “fossil” record of earths magnetism at current time o Using this evidence, scientists have determined the pole wanders, and even switches magnetism over time Magnetic orientation of old rocks does not match what it should be were they formed in that spot today This discovery served as a large factor in legitimizing the theory of continental drift. Question 2: The Juan de Fuca Ridge and Plate Located off the coast of Washington and BC Juan de Fuca plate is between North American Plate and Pacific Plate o Juan de Fuca Ridge is divergent boundary (mid-ocean ridge) between Pacific plate and Juan de Fuca Plate o Juan de Fuca PLATE goes under North American plate (@ cascadia subduction zone) Has all three types of plate boundaries in close proximity Moving 2-3 cm / year Cascadia subduction zone o Convergent plate boundary stretching from North Vancouver Island to Northern  California o Separates the Juan de Fuca and North American plates o Denser ocean plate is subducting under Continental plate o Earthquakes and stratovolcanoes San andreas fault o Transform fault o sliding along each other. The majority of this kind of fault are found in the ocean, however the few that are on land pose a huge risk because they cause shallow focus earthquakes, which result in more damage on the surface than comparable deeper focus earthquakes
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Question 3: Age of Oceanic Crustal Rocks Anomalies in the paleomagnetic record are stripes showing movement o Caused by geomagnetic reversal o Use these stripes to date the plates Radioactive decay measurements are used to confirm this Use the GPS system to detect changes in the distance across oceans, which shows us that  they are changing every year See that rock along the mid ocean ridges is very young, and we can see that rock in the  ocean floor is overall quite young o This is because the old rock gets subducted under continental plates as it gets  pushed out by new igneous rock being formed along the mid ocean ridge.
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