( ( Most extinctions ) ( ( are ( thought ( to ( have ( resulted ( from ( ( environmental changes ) ( that ( ( affected ( the species ) ) ( in ( either ( of ( two ways ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJS Most) (NNS extinctions)) (VP (VBP are) (VP (VBN thought) (S (VP (TO to) (VP (VB have) (VP (VBN resulted) (PP (IN from) (NP (NP (JJ environmental) (NNS changes)) (SBAR (WHNP (WDT that)) (S (VP (VBD affected) (NP (DT the) (NN species)) (PP (IN in) (NP (NP (DT either)) (PP (IN of) (NP (CD two) (NNS ways)))))))))))))))) (. .)))
Most extinctions are thought to have resulted from environmental changes that affected the species in either of two ways.
(ROOT (S (NP (JJ Environmental) (NNS changes)) (VP (VBZ is) (ADJP (RBS most) (JJ responsible) (PP (IN for) (NP (NP (DT the) (NN extinction)) (PP (IN of) (NP (NP (JJS most) (NNS species)) (PP (IN of) (NP (NNS plants) (CC and) (NNS animals))))) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (VP (VBN lived) (PP (IN on) (NP (NN earth))))))))))) (. .)))
Environmental changes is most responsible for the extinction of most species of plants and animals that have lived on earth.