( ( Eukaryotic cells ) ( probably ( ( evolved ( ( ( about ( 2 billion ) ) years ) ago ) ) . ) ) )
(ROOT (S (NP (JJ Eukaryotic) (NNS cells)) (ADVP (RB probably)) (VP (VBD evolved) (ADVP (NP (QP (RB about) (CD 2) (CD billion)) (NNS years)) (RB ago))) (. .)))
Eukaryotic cells probably evolved about 2 billion years ago.
(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))))) (. .)))