( They ( ( admit ( that ( ( both ( ( ( the vegetable ) and ) ( the ( animal species ) ) ) ) ( have ( ( changed , ) ( for ( ( in ( some ( of ( ( the strata ) ( of ( the earth ) ) ) ) ) ) ( they ( have ( discovered ( plants ( which ( ( ( existed ( in ( the past ) ) ) and ) ( ( are now ) extinct ) ) ) ) ) ) ) ) ) ) ) ) ) ) ; ) )
(ROOT (S (NP (PRP They)) (VP (VBP admit) (SBAR (IN that) (S (NP (CC both) (NP (DT the) (NN vegetable)) (CC and) (NP (DT the) (NN animal) (NN species))) (VP (VBP have) (VP (VBN changed) (, ,) (SBAR (IN for) (S (PP (IN in) (NP (NP (DT some)) (PP (IN of) (NP (NP (DT the) (NN strata)) (PP (IN of) (NP (DT the) (NN earth))))))) (NP (PRP they)) (VP (VBP have) (VP (VBN discovered) (NP (NP (NNS plants)) (SBAR (WHNP (WDT which)) (S (VP (VP (VBD existed) (PP (IN in) (NP (DT the) (NN past)))) (CC and) (VP (VBP are) (ADVP (RB now)) (ADJP (JJ extinct)))))))))))))))) (: ;)))
They admit that both the vegetable and the animal species have changed, for in some of the strata of the earth they have discovered plants which existed in the past and are now extinct;
(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.