( ( Oceanic crust ) ( ( ( is primarily ) ( composed ( of ( ( ( ( mafic rocks ) , ) or ) sima ) ) ) ) . ) )
(ROOT (S (NP (NNP Oceanic) (NNP crust)) (VP (VBZ is) (ADVP (RB primarily)) (VP (VBN composed) (PP (IN of) (NP (NP (JJ mafic) (NNS rocks)) (, ,) (CC or) (NP (NN sima)))))) (. .)))
Oceanic crust is primarily composed of mafic rocks, or sima.
(ROOT (S (NP (NP (DT The) (NN earth) (POS 's)) (NN crust)) (VP (VBZ is) (VP (VBN composed) (PP (IN of) (NP (JJ igneuos) (NN rock))))) (. .)))