( Half-life ( ( is ( ( ( the amount ) ( of time ) ) ( it ( ( takes ( for ( half ( of ( ( the amount ) ( of ( a substance ) ) ) ) ) ) ) ( to decay ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Half-life)) (VP (VBZ is) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NN time))) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (DT a) (NN substance))))))) (PP (TO to) (NP (NN decay)))))))) (. .)))
Half-life is the           amount of time it takes for half of the           amount of a substance to decay.
(ROOT (S (NP (DT The) (NN term) (NN half-life)) (VP (VBZ decribes) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN time)) (VP (VBN required) (PP (IN for) (NP (NP (NN half)) (PP (IN of) (NP (DT the) (JJ original) (NN material))))) (PP (TO to) (NP (NP (NN decay)) (PP (IN in) (NP (DT an) (NN isotope)))))))))) (. .)))