( ( At ( ( lease ( five times ) ) ( in ( ( the history ) ( of ( life ( on ( earth ( mass ( extinction event ) ) ) ) ) ) ) ) ) ) ( s ( ( have occurred ) . ) ) )
(ROOT (S (PP (IN At) (NP (NP (NN lease)) (NP (CD five) (NNS times)) (PP (IN in) (NP (NP (DT the) (NN history)) (PP (IN of) (NP (NP (NN life)) (PP (IN on) (NP (NN earth) (NN mass) (NN extinction) (NN event))))))))) (NP (PRP s)) (VP (VBP have) (VP (VBN occurred))) (. .)))
At lease five times in the history of life on earth mass extinction event s have occurred.
(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)))))) (. .)))