( But ( they ( ( are ( ( strong enough ) ( to ( alter ( ( the ( gravitational center ) ) ( of ( the earth ) ) ) ) ) ) ) . ) ) )
(ROOT (S (CC But) (NP (PRP they)) (VP (VBP are) (ADJP (JJ strong) (RB enough) (S (VP (TO to) (VP (VB alter) (NP (NP (DT the) (JJ gravitational) (NN center)) (PP (IN of) (NP (DT the) (NN earth))))))))) (. .)))
But they are strong enough to alter the gravitational center of the earth.
(ROOT (S (NP (JJ Strong) (JJ gravitational) (NNS fields)) (VP (VBP are) (ADJP (JJ capable) (PP (IN of) (S (VP (VBG altering) (NP (NP (DT the) (NN rate)) (PP (IN of) (NP (NN time) (NN passing))))))))) (. .)))