( ( return ( to ( top ( Mass extinctions ) ) ) ) ( ( in ( ( Earth 's ) history ) ) ( ( ( ( ( At least ) five ) ( major episodes ) ) ( of ( mass extinction ) ) ) ( ( have ( occurred ( since ( life ( developed ( on Earth ) ) ) ) ) ) . ) ) ) )
(ROOT (S (NP (NP (NN return)) (PP (TO to) (NP (JJ top) (NNP Mass) (NNS extinctions)))) (PP (IN in) (NP (NP (NNP Earth) (POS 's)) (NN history))) (NP (NP (QP (IN At) (JJS least) (CD five)) (JJ major) (NNS episodes)) (PP (IN of) (NP (JJ mass) (NN extinction)))) (VP (VBP have) (VP (VBN occurred) (PP (IN since) (NP (NP (NN life)) (VP (VBN developed) (PP (IN on) (NP (NNP Earth)))))))) (. .)))
return to top Mass extinctions in Earth's history At least five major episodes of mass extinction have occurred since life developed on Earth.
(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)))))) (. .)))