( ( ( ( ( ( At around ) 4 ) billion ) years ) ago ) ( we ( ( have ( ( ( the ( first evidence ) ) ( of life ) ) ( that ( ( was once ) ( living ( in ( ( the oceans ) ( of Earth ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (ADVP (NP (QP (IN At) (IN around) (CD 4) (CD billion)) (NNS years)) (RB ago)) (NP (PRP we)) (VP (VBP have) (NP (NP (DT the) (JJ first) (NN evidence)) (PP (IN of) (NP (NN life))) (SBAR (WHNP (WDT that)) (S (VP (VBD was) (ADVP (RB once)) (VP (VBG living) (PP (IN in) (NP (NP (DT the) (NNS oceans)) (PP (IN of) (NP (NNP Earth))))))))))) (. .)))
At around 4 billion years ago we have the first evidence of life that was once living in the oceans of 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))))) (. .)))