( ( Looking ( at ( ( the ( paleologic record ) ) ( -LRB- ( really ( ( old rocks ) -RRB- ) ) ) ) ) ) ( , ( scientists ( ( have ( discovered ( that ( ( the ( magnetic ( North Pole ) ) ) ( ( has completely ) ( ( switched ( with ( the ( magnetic ( South Pole ) ) ) ) ) ( several times ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (S (VP (VBG Looking) (PP (IN at) (NP (NP (DT the) (JJ paleologic) (NN record)) (PRN (-LRB- -LRB-) (ADVP (RB really)) (NP (JJ old) (NNS rocks)) (-RRB- -RRB-)))))) (, ,) (NP (NNS scientists)) (VP (VBP have) (VP (VBN discovered) (SBAR (IN that) (S (NP (DT the) (JJ magnetic) (NNP North) (NNP Pole)) (VP (VBZ has) (ADVP (RB completely)) (VP (VBN switched) (PP (IN with) (NP (DT the) (JJ magnetic) (NNP South) (NNP Pole))) (NP (JJ several) (NNS times)))))))) (. .)))
Looking at the paleologic record (really old rocks), scientists have discovered that the magnetic North Pole has completely switched with the magnetic South Pole several times.
(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))))) (. .)))