( ( Introduction Scientists ) ( ( have ( ( ( found ( ( evidence ( of ( ( at least ) five ) ) ) ( ` ( mass extinctions ) ) ) ) ' ) ( since ( ( the earth ) ( was formed ) ) ) ) ) . ) )
(ROOT (S (NP (NN Introduction) (NNS Scientists)) (VP (VBP have) (VP (VBN found) (S (NP (NP (NN evidence)) (PP (IN of) (NP (QP (IN at) (JJS least) (CD five))))) (`` `) (ADJP (RB mass) (JJ extinctions))) ('' ') (SBAR (IN since) (S (NP (DT the) (NN earth)) (VP (VBD was) (VP (VBN formed))))))) (. .)))
Introduction Scientists have found evidence of at least five 'mass extinctions' since the earth was formed.
(ROOT (S (NP (EX There)) (VP (VBP have) (VP (VBN been) (NP (CD five) (JJ major) (JJ massive) (NNS extinctions)) (SBAR (IN since) (S (NP (NN life)) (VP (VBD began) (PP (IN on) (NP (NN earth)))))))) (. .)))