( ( ( Pole Reversal ) ( Although ( ( most ( of us ) ) ( ( are ( familiar ( with ( the ( North ( Pole ( and ( South Pole ) ) ) ) ) ) ) ) ( in ( their ( present locations ) ) ) ) ) ) ) ( , ( ( ( the ( Earth 's ) ) ( magnetic poles ) ) ( ( have ( ( ( switched ( several times ) ) ( throughout ( geologic history ) ) ) ( as ( is ( indicated ( by ( ( magnetic stripes ) ( on ( the ( ocean floor ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (NP (NNP Pole) (NNP Reversal)) (IN Although) (S (NP (NP (JJS most)) (PP (IN of) (NP (PRP us)))) (VP (VBP are) (ADJP (JJ familiar) (PP (IN with) (NP (DT the) (NNP North) (NNP Pole) (CC and) (NNP South) (NNP Pole)))) (PP (IN in) (NP (PRP$ their) (JJ present) (NNS locations)))))) (, ,) (NP (NP (DT the) (NN Earth) (POS 's)) (JJ magnetic) (NNS poles)) (VP (VBP have) (VP (VBN switched) (NP (QP (JJ several) (NNS times))) (PP (IN throughout) (NP (JJ geologic) (NN history))) (SBAR (IN as) (S (VP (VBZ is) (VP (VBN indicated) (PP (IN by) (NP (NP (JJ magnetic) (NNS stripes)) (PP (IN on) (NP (DT the) (NN ocean) (NN floor))))))))))) (. .)))
Pole Reversal Although most of  us are familiar with the North Pole and South Pole in their present locations, the Earth's magnetic poles have switched several times throughout geologic history as is indicated by magnetic stripes on the ocean floor.
(ROOT (S (NP (NP (DT The) (NN earth) (POS 's)) (JJ magnetic) (NNS poles)) (VP (VBP have) (VP (VBN switched) (NP (NNS places)) (ADVP (RB repeatedly)) (PP (IN in) (NP (DT the) (NN past))))) (. .)))