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EPSC 201 – SHORT ANSWERSPaleomagnetism and geomagnetic pole paths
If you payed attention to the biology(plants and animals) across continents you seesimilarities Seems to have fit together for a timeSouth America and Africa split apart somethinglike 160 million years ago, they share animalsimilarities up until this pointMostly birdsThere are common geological terranesSame rocks in east Africa and brazilSame age same kindSimilar geology in Mountain belts of north America as in AfricaUp until 180 million years ago, then they differUserocks from different continents to find the magnetic pole at the time the rock was form, Record the magnetic change over timeTurns out these curves line up if you reassemblethe continents
PaleomagnetismMagnetic fields of ancient rocks indicate the orientation of the magnetic field relative to the rock, at the time the rock formed. This record preserved in rock is paleomagnetism. In a rock that formed millions of years ago, the orientation of the dipole representing the magneticfield of the rock is not the same as that of present day Earth. When lava starts to cool and solidify into rock, tiny crystals begin to grow. At first, thermal energy cause the tiny magnetic dipole associated with each crystal to wobble chaotically. Eventually, the rock cools, dipoles slow down and like tiny compass needles, align with the earth’s magnetic field. Since magnetic dipoles of all grains point in the same direction, they add together and produce a measurable field. Paleopole Supposed position of the earth’s magnetic north pole in the past. Geologists wanted to track the change in position of the paleopole over time. They measure the paleomagnetism in a succession of rocks of different ages from the same location on a continent and plotted the successive positions of dated paleopoles on a map. This traced out a curving linethat came to be known as an apparent polar-wander path. They found that each continent has a different apparent polar-wander path. They realised it is not the pole that moves relative to fixed continents, but rather the continents that move relativeto a fixed pole. Since each continent has its own unique polar-wander path, the continents must move with respect to each other.Earth’s magnetic fieldFlow in the liquid outer core creates the magnetic field.oIt is similar to the field produced by a bar magnetoThe magnetic pole is tilted ~11.5 from the axis of rotationGeographic and magnetic poles are not parallel.A compass points to magnetic N, not geographic N.The difference between geographic N and magnetic N is called declination. It depends on:oAbsolute position of the two polesGeographic northMagnetic northLongitudeCurved field lines cause a magnetic needle to tilt.