( Evidence ( ( exists ( that ( ( ( the ( earth 's ) ) ( magnetic poles ) ) ( ( switch ( occasionally ( , ( as ( ( old samples ) ( often ( show ( ( magnetic patterns ) ( that ( ( do not ) ( match ( with he ) ) ) ) ) ) ) ) ) ) ) ) ( current ( magnetic alignment ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Evidence)) (VP (VBZ exists) (SBAR (IN that) (S (NP (NP (DT the) (NN earth) (POS 's)) (JJ magnetic) (NNS poles)) (VP (VBP switch) (PRN (ADVP (RB occasionally)) (, ,) (SBAR (IN as) (S (NP (JJ old) (NNS samples)) (ADVP (RB often)) (VP (VBP show) (NP (NP (JJ magnetic) (NNS patterns)) (SBAR (WHNP (WDT that)) (S (VP (VBP do) (RB not) (VP (VB match) (PP (IN with) (NP (PRP he)))))))))))) (NP (JJ current) (JJ magnetic) (NN alignment)))))) (. .)))
Evidence exists that the earth's magnetic poles switch occasionally, as old samples often show magnetic patterns that do not match with he current magnetic alignment.
(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))))) (. .)))