( ( ( Obligatory death ) ( due ( to ( ( ( senescence or ) normal ) aging ) ) ) ) ( ( ( may not ) ( have ( ( evolved ( during ( ( the ( first ( billion years ) ) ) ( of life ) ) ) ) ( on earth ) ) ) ) . ) )
(ROOT (S (NP (NP (JJ Obligatory) (NN death)) (ADJP (JJ due) (PP (TO to) (NP (ADJP (JJ senescence) (CC or) (JJ normal)) (NN aging))))) (VP (MD may) (RB not) (VP (VB have) (VP (VBN evolved) (PP (IN during) (NP (NP (DT the) (JJ first) (CD billion) (NNS years)) (PP (IN of) (NP (NN life))))) (PP (IN on) (NP (NN earth)))))) (. .)))
Obligatory death due to senescence or normal aging may not have evolved during the first billion years of life on earth.
(ROOT (S (NP (DT The) (JJ first) (VBG living) (NNS cells)) (VP (MD may) (VP (VB have) (VP (VBN evolved) (ADVP (NP (QP (RB around) (CD 4) (CD billion)) (NNS years)) (RB ago))))) (. .)))