( ( ( Earth 's ) atmosphere ) ( ( ( is mainly ) ( ( nitrogen and ) oxygen ) ) . ) )
(ROOT (S (NP (NP (NNP Earth) (POS 's)) (NN atmosphere)) (VP (VBZ is) (ADVP (RB mainly)) (NP (NN nitrogen) (CC and) (NN oxygen))) (. .)))
Earth's atmosphere is mainly nitrogen and oxygen.
(ROOT (S (NP (NN Oxygen) (CC and) (NN nitrogen)) (VP (VBP make) (PRT (RP up)) (NP (NP (JJS most)) (PP (IN of) (NP (NP (DT the) (NN earth) (POS 's)) (NN atmosphere))))) (. .)))
Oxygen and nitrogen make up most of the earth's atmosphere.