( ( ( ( ( There ( are ( ( five ( ( widely recognized ) ( major ( mass ( extinction episodes ) ) ) ) ) ( in ( ( the ( Earth 's ) ) history ) ) ) ) ) , ) and ) ( ( many scientists ) ( believe ( that ( we ( ( have now ) ( entered ( the sixth ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (EX There)) (VP (VBP are) (NP (NP (CD five) (ADJP (RB widely) (VBN recognized)) (JJ major) (JJ mass) (NN extinction) (NNS episodes)) (PP (IN in) (NP (NP (DT the) (NN Earth) (POS 's)) (NN history)))))) (, ,) (CC and) (S (NP (JJ many) (NNS scientists)) (VP (VBP believe) (SBAR (IN that) (S (NP (PRP we)) (VP (VBP have) (ADVP (RB now)) (VP (VBN entered) (NP (DT the) (JJ sixth)))))))) (. .)))
There are five widely recognized major mass extinction episodes in the Earth's history, and many scientists believe that we have now entered the sixth.
(ROOT (S (NP (CD Five) (JJ mass) (NNS distinctions)) (VP (VBP have) (ADVP (RB radically)) (VP (VBN altered) (NP (NP (DT the) (NN history)) (PP (IN of) (NP (NN life)))))) (. .)))