( This ( ( is ( because ( ( ( the ( earth 's ) ) ( geographic ( pole ( -LRB- ( ( ( the axis ) ( ( about which ) ( it rotates ) ) ) -RRB- ) ) ) ) ) ( ( is not ) ( in ( ( ( the ( same place ) ) ( as ( its ( magnetic pole ) ) ) ) ( -LRB- ( ( ( the place ) ( where ( ( ( the ( magnetic lines ) ) ( of force ) ) ( emerge ( from ( the earth ) ) ) ) ) ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (SBAR (IN because) (S (NP (NP (DT the) (NN earth) (POS 's)) (JJ geographic) (NN pole) (PRN (-LRB- -LRB-) (NP (NP (DT the) (NNS axis)) (SBAR (WHPP (IN about) (WHNP (WDT which))) (S (NP (PRP it)) (VP (VBZ rotates))))) (-RRB- -RRB-))) (VP (VBZ is) (RB not) (PP (IN in) (NP (NP (DT the) (JJ same) (NN place)) (PP (IN as) (NP (PRP$ its) (JJ magnetic) (NN pole))) (PRN (-LRB- -LRB-) (NP (NP (DT the) (NN place)) (SBAR (WHADVP (WRB where)) (S (NP (NP (DT the) (JJ magnetic) (NNS lines)) (PP (IN of) (NP (NN force)))) (VP (VBP emerge) (PP (IN from) (NP (DT the) (NN earth))))))) (-RRB- -RRB-)))))))) (. .)))
This is because the earth's geographic pole (the axis about which it rotates) is not in the same place as its magnetic pole (the place where the magnetic lines of force emerge from the earth).
(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))))) (. .)))